Altitude zones of Mexico

 Other  4 Responses »
Dec 172016
 

Most of Mexico is above 1000 m (about 3300 ft) in elevation; as a result most of Mexico has a more temperate climate than might be expected given its latitude.

The famous explorer Alexander von Humboldt, one of the founding fathers of physical geography and meteorology, was the first to describe the vertical differentiation of climatic and vegetation zones in Mexico. Writing in 1811, he proposed the terms tierra caliente, tierra templada, and tierra fría, still widely used by non-specialists today.

Tierra caliente (hot land) includes all areas under about 900 m (3000 ft). These areas generally have a mean annual temperature above 25°C (77°F). Their natural vegetation is usually either tropical evergreen or tropical deciduous forest. Farms produce tropical crops such as sugar-cane, cacao and bananas.

Altitude zones

Altitude zones. Copyright John Wiley & Sons Inc. 2000.

Tierra templada (temperate land) is the area between 900 and 1800 m (3000 to 6000 ft) where mean annual temperatures are usually between about 18°C and 25°C (64°F to 77°F). The natural vegetation in these zones is temperate forest, such as oak and pine-oak forest. Farms grow crops such as corn (maize), beans, squash, wheat and coffee.

Tierra fria (cold land) is over 1800 m (6000 ft) where mean annual temperatures are in the range 13°–18°C (55°–64°F). At these altitudes pine and pine-fir forests are common. Farm crops include barley and potatoes. On the highest mountain tops, above the tierra fría is tierra helada, frosty land.

Even higher, and almost permanently under snow and ice, is the tierra nevada, snow-covered land.

Hurricane forecast and names for 2016

 Updates to Geo-Mexico  2 Responses »
May 122016
 

The 2016 hurricane season in Mexico for Pacific coast storms starts on 15 May and lasts until 30 November. For Atlantic storms, the hurricane season extends from 1 June to 30 November, though most hurricane activity is concentrated in the months from July to September. Hurricanes are also known as typhoons or tropical cyclones.

The table shows the World Meteorological Organization’s official list of 2016 tropical storm and hurricane names. Note that male and female names alternate. Names are often reused in future years, with the exception of the names of any particularly violent storms, which are officially “retired” from the list for a long time.

2016 Hurricane Names for the Atlantic, Gulf of Mexico and Caribbean
AlexGastonLisaRichard
BonnieHermineMatthewShary
ColinIanNicoleTobias
DanielleJuliaOttoVirginia
EarlKarlPaulaWalter
Fiona

2016 Hurricane Names for the Eastern Pacific
AgathaGeorgetteMadelineTina
BlasHowardNewtonVirgil
CeliaIvetteOrleneWinifred
DarbyJavierPaineXavier
EstelleKayRoslynYolanda
FrankLesterSeymourZeke

saffir-simpson-scale

In their early season forecast for this year, Philip Klotzbach and William Gray, researchers at Colorado State University,  expect hurricane activity in the Atlantic to be near-normal (ie close to the 30-year average). They predict that in the 2016 season 13 named storms will form in the Atlantic: 5 tropical storms, 6 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 2 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). These forecasts will be updated on 2 June and 31 July.

Last year’s Atlantic hurricane season was slightly below average in activity with 11 named storms: 5 tropical storms, 4 moderate hurricanes and 2 severe hurricanes. On the other hand, the 2015 Pacific hurricane season was the second most active on record, with 26 named storms, including 11 severe hurricanes.

In 2016, for the Pacific coast, Mexico’s National Meteorological Service (Servicio Metrológico Nacional, SMN) is expecting 17 named storms: 8 tropical storms, 5 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 4 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale).

For the Atlantic coast, SMN) is expecting 13 named storms: 7 tropical storms, 4 moderate hurricanes and 2 severe hurricanes. On both coasts, these predictions indicate a slight increase in storm activity compared to long-term averages. The SNM publishes regular updates on hurricane activity (in Spanish) on its webpage and via its Twitter account: @huracanconagua.

Hurricanes and other climatological phenomena are analyzed in chapters 4 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico. Buy your copy today, so you have a handy reference guide available whenever you need it.

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How will this year’s strong El Niño affect Mexico?

 Updates to Geo-Mexico  4 Responses »
Nov 232015
 

As we discussed in this earlier post, historical analysis combined with greater climatological understanding shows that many of the worst droughts and floods in Mexico have been associated with either El Niño Southern Oscillation (ENSO) events or with the related Pacific-North American Oscillation. Perhaps 65% of the variability of Mexican climate results from changes in these large-scale circulations.

The World Meteorological Organization (WMO) says the 2015-2016 ENSO is expected to be one of the three most powerful ENSO events since 1950 with effects that will last for up to eight months.

What will this winter’s El Niño bring? 

  • slightly higher ocean water temperature off west coast; some fish species may migrate northwards
  • some winter rain in north-west
  • increased winter storms, and cooler temperatures, along east coast; risk of flooding, mudslides
  • reduced summer rainfall in Mexico’s central highlands; risk of drought and lower crop yields

This winter, according to the Center for Scientific Investigation and Higher Education of Ensenada (CICESE), the Baja California Peninsula is likely to receive more rain than usual during this year’s very strong ENSO (El Niño) event.

The distribution of fish species is likely to change as the ocean temperatures are higher than usual, resulting in the migration of some species, leaving fewer fish off the coast of Baja California, one of the world’s most important commercial and sports fishing zones. Sardine fishermen may have a difficult season, incurring greater costs as they try to locate viable schools of fish.

A NASA climatologist predicts that California (USA) will be on the receiving end of more winter storms (January-March), and heavier rain, than usual. This increases the risk of hazardous mudslides in some coastal communities. It could also mean more mosquitoes, and an increased chance of contracting dengue fever or chikungunya.

What is the longer term outlook?

The first map shows likely precipitation anomalies for early next year (Spring). Areas shaded brown are areas expected to receive less rainfall than normal. Areas shaded light blue through green are predicted to get more rain than usual.

Spring precipitation anomalies

Spring precipitation anomalies in a strong El Niño year. Source: CNA

The second map shows summer precipitation anomalies. A significant reduction in rainfall is expected across most of central Mexico, though some areas in southern Mexico will likely get more rainfall than normal.

Summer precipitation anomalies in a strong El Niño year. Source: CNA

Summer precipitation anomalies in a strong El Niño year. Source: CNA

We end with one piece of good news for our more active readers. Previous El Niño events have brought great surfing to the west coast of Mexico, so make your travel and hotel plans as soon as possible.

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Mexico has highest rate of death from lightning strikes in the Americas

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Aug 062015
 

Last year, three Mexico City climate researchers published a comprehensive study of the 7300+ deaths due to lightning in Mexico during the period 1979 to 2011.

In “Deaths by Lightning in Mexico (1979–2011): Threat or Vulnerability?“, G. B. Raga, M. G. de la Parra and Beata Kucienska examined the distribution of fatalities due to lighting, looking for links to population density, vulnerability and other factors.

The number of deaths from lightning averaged 230 a year for the period studied. Given Mexico’s population, this means a rate of 2.72 fatalities from lightning for every million people. This is the highest rate in the Americas.

Fatalities were not distributed evenly. Seven of Mexico’s 32 states accounted for 60% of all lightning fatalities. Almost one-quarter of all deaths from lightning occurred in the State of México. Other states with high rates included Michoacán, Oaxaca and Guanajuato.

More than 45% of all deaths from lightning were young males under the age of 25 (with those aged 10 to 19 at particular risk). Overall, far fewer females died from lightning than males, though for females, too, the highest rates were for the under-25 age group.

Most deaths happened in the first half of the rainy season, between June and August, when thunderstorms are most likely.

Lightning incidence, North America, 2012-2014

Lightning incidence, North America, 2012-2014. Credit: Vaisala

What do all these numbers mean?

The incidence of lightning strikes in not equal across the country. For example, in the period 2012-2014 (see map) there were far more lightning events in in central and southern Mexico than in the northern part of the country and the Baja California Peninsula. This means that there is no clear connection between deaths by lightning and population density. However, neither is there a clear connection between deaths by lightning and the places where most lightning strikes occur.

The key factor is not just how likely a lightning strike is to occur in a particular place but also how vulnerable the local populace is. Some sectors of the population are much more vulnerable than others. Those working outdoors, for example, are at higher risk than those working indoors. This makes rural workers more vulnerable than urban workers. It also makes younger people more vulnerable than older people.

Education and awareness also play a part. Many countries have seen a dramatic fall in deaths from lightning as a direct result of launching campaigns to make people more aware and provide education about safety precautions. In the USA, fewer than 40 people now die each year from lightning, compared to about 400 in the 1930s, when the population was smaller.

For this reason, the study also concluded that the large number of deaths in Mexico is partly due to “the government’s failure to implement education and prevention strategies in communities living and working in vulnerable conditions”. Sadly, this means that there will probably be further tragic incidents similar to the one that took the lives of several members of the same family last month in the remote mountainous community of Mesa Cuata in Guanajuato.

Reference:

G. B. Raga, M. G. de la Parra, and Beata Kucienska, 2014: “Deaths by Lightning in Mexico (1979–2011): Threat or Vulnerability?”. Weather, Climate & Society, 6, 434–444.

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Hurricane forecast and names for 2015

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Apr 202015
 

The 2015 hurricane season in Mexico for Pacific coast storms starts on 15 May and lasts until 30 November. For Atlantic storms, the hurricane season extends from 1 June to 30 November, though most hurricane activity is concentrated in the months from July to September. Hurricanes are also known as typhoons or tropical cyclones.

The table shows the World Meteorological Organization’s official list of 2015 tropical storm and hurricane names. Note that male and female names alternate. Names are often reused in future years, with the exception of the names of any particularly violent storms, which are officially “retired” from the list for a long time.

2015 Hurricane Names for the Atlantic, Gulf of Mexico and Caribbean
AnaGraceLarryRose
BillHenriMindySam
ClaudetteIdaNicholasTeresa
DannyJoaquinOdetteVictor
ErikaKatePeterWanda
Fred

2015 Hurricane Names for the Eastern Pacific
AndresGuillermoMartyTerry
BlancaHildaNoraVivian
CarlosIgnacioOlafWaldo
DoloresJimenaPatriciaXina
EnriqueKevinRickYork
FeliciaLindaSandraZelda

In their early season forecast for this year, Philip Klotzbach and William Gray, researchers at Colorado State University,  expect hurricane activity in the Atlantic to be below the 1981-2012 average. They predict that in the 2015 season 7 named storms will form in the Atlantic: 4 tropical storms, 2 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 1 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). These forecasts will be updated on 2 June and 31 July.

saffir-simpson-scaleAs expected, Pacific Ocean hurricanes were more common than usual in 2014, because it was an El Niño year. In 2014, there were 22 named storms (the highest total for 22 years), including a record-typing 16 hurricanes, of which 9 were major hurricanes. Hurricane activity in 2015 is also expected to be higher than the long-term average.

In 2015, for the Pacific coast, Mexico’s National Meteorological Service (Servicio Metrológico Nacional, SMN) is expecting 19 named storms: 8 tropical storms, 7 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 4 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). The SNM publishes regular updates on hurricane activity (in Spanish) on its webpage and via its Twitter account: @huracanconagua.

How accurate was the 2014 forecast?

The early season (May) prediction for 2014 (last year) was for 9 named storms in the Atlantic: 6 tropical storms, 2 moderate hurricanes and 1 severe hurricanes. This prediction proved to be the fairly accurate. In reality, the 2014 Atlantic season had 8 named storms: 2 tropical storms, 4 moderate hurricanes and 2 severe hurricanes. 

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Monitoring air pollution in Guadalajara

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Jun 162014
 

Air pollution in the city of Guadalajara, the state capital of Jalisco, has worsened over the past decade, though there are some recent signs of improvement :

The Jalisco Environmental Agency now has a webpage where residents and travelers alike can now monitor Guadalajara’s air quality on an hourly basis. Readings for 10 stations are superimposed on a basemap on that page, together with links to graphs showing recent trends and other meteorological data. Tabs above the map also give a link to the current wind conditions across the city. Historical data (in Spanish) can also be accessed via the link to “Datos”.

Screenshot of Guadalajara air monitoring webpage

Screenshot of Guadalajara air monitoring webpage. Note: Two stations are shown as undergoing maintenance.

The map provides summary data in IMECAs, which stands for Índice Metropolitano de la Calidad del Aire (Metropolitan Index of Air Quality). IMECAs are a compound index combining measurements of concentrations of ozone (O3), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO) and particles smaller than 10 micrometers (PM10).

In Guadalajara, formal smog alerts are issued if average readings rise above 150 IMECAs (“Very Bad”) for more than two consecutive hours. If readings rise above 200 IMECAs (“Extremely Bad”), then “serious alerts” impose restrictions on vehicle use and may lead to the suspension of school classes.

In Guadalajara, the worst air quality tends to be in the southern and eastern sections of the city. It also tends to occur in the months of April and May, immediately before the rainy season gets underway. The webpage system gives everyone an easy way to check these assertions!

In Guadalajara, mitigation efforts are centered mainly on reducing vehicle emissions (partly by stricter emissions testing and verification, and partly by improvements to the public transport network) since they are the main source of pollution. To date, there are no plans in Guadalajara to introduce a “Day without car” program similar to that in Mexico City:

Teaching idea

Use the Jalisco Environment Agency webpage to monitor Guadalajara’s air pollution and identify any patterns or trends related to air pollution in the city. Consider suggesting one or more hypotheses, such as “Air pollution gets worse in the afternoon”, or “The level of air pollution in eastern Guadalajara is worse than in western Guadalajara”, before testing your ideas using the online data.

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Hurricane names and forecast for 2014

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Apr 172014
 

The 2014 hurricane season in Mexico for Pacific coast storms starts on 15 May and lasts until 30 November. For Atlantic storms, the hurricane season extends from 1 June to 30 November, though most hurricane activity is concentrated in the months from July to September. Hurricanes are also known as typhoons or tropical cyclones.

In 2013 only two hurricanes (Manuel and Ingrid) hit Mexico, but they hit simultaneously in September, leading to more than 100 storm-related deaths and millions of dollars worth of property damage in several states, especially Guerrero.

The table shows the World Meteorological Organization’s official list of 2014 hurricane names. Note that male and female names alternate. Names are often reused in future years, with the exception of the names of any particularly violent storms, which are officially “retired” from the list for a long time.

2014 Hurricane Names for the Atlantic, Gulf of Mexico and Caribbean
ArthurGonzaloLauraRene
BerthaHannaMarcoSally
CristobalIsaiasNanaTeddy
DollyJosephineOmarVicky
EduourdKylePauletteWilfred
Fay

2014 Hurricane Names for the Eastern Pacific
AmandaGenevieveMarinaTrudy
BorisHernanNorbertVance
CristinaIselleOdileWinnie
DouglasJulioPoloXavier
ElidaKarinaRachelYolanda
FaustoLowellSimonZeke

For the Atlantic coast, Mexico’s National Meteorological Service (Servicio Metrológico Nacional, SMN) is expecting 10 named storms: 3 tropical storms, 5 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 2 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale).

In their early season forecast for this year, Philip Klotzbach and William Gray, researchers at Colorado State University,  expect hurricane activity in the Atlantic to be significantly below the 1981-2012 average. They write that, “The tropical Atlantic has… cooled over the past several months, and the chances of a moderate to strong El Niño event this summer and fall appear to be quite high…. Historical data indicate fewer storms form in these conditions.” They predict that in the 2014 season 9 named storms will form in the Atlantic: 6 tropical storms, 2 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 1 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). These forecasts will be updated on 2 June and 31 July.

saffir-simpson-scalePacific Ocean hurricanes tend to be more common in El Niño years, so this year may be more active than usual. For the Pacific coast, Mexico’s National Meteorological Service (Servicio Metrológico Nacional, SMN) is expecting 15 named storms: 5 tropical storms, 7 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 3 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). The SNM publishes regular updates on hurricane activity (in Spanish) on its webpage and via its Twitter account: @huracanconagua.

How accurate was the 2013 forecast?

The early season (May) prediction for 2013 (last year) was for 18 named storms in the Atlantic: 9 tropical storms, 5 moderate hurricanes and 4 severe hurricanes. This prediction proved to be the least accurate forecast in recent years. In reality, the 2013 Atlantic season had 14 named storms: 1 tropical depression, 11 tropical storms, 2 moderate hurricanes and 0 severe hurricanes. Klotzbach and Gray have since looked at the possible reasons for the poor forecast and concluded that, “It appears that the primary reason was the most significant spring weakening observed since 1950 of the Atlantic thermohaline circulation.” A summary of their findings is available here.

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Mexico’s January weather serves as a long-range forecast

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Jan 042014
 

Many Mexicans use January’s weather to forecast what the weather will be like for the rest of the year.

Many Mexicans, especially campesinos (peasant farmers), who are closer to the land than most, believe that the weather during the month of January serves as a long-range forecast for the entire year. The precise prediction system, known as las cabañuelas, is thought to be based on long cycles of observations carried out in an age when people depended far more on the weather than they do today. The system is quite complicated.

The first twelve days of January are known as las cabañuelas “a derechas”. The weather on January 1 foretells the likely weather for the rest of the month. The weather on January 2 predicts the weather for February and so on, with the weather of January 12 suggesting likely conditions for December. The next twelve days (January 13 to 24 inclusive) are known as las cabañuelas “a rataculas”. This time, the weather of January 13 foretells December, that of January 14 November, and so on.

Jan 18: Pondering a miserable July

Next, each of the six days from January 25 to January 30 inclusive is divided at noon. The morning of January 25 represents January, the afternoon February. The morning of January 26 hints at March’s weather, while the afternoon applies to April’s, and so on.

Finally, even the 24 hours of January 31 are used. Each hour in the morning will be reflected in the weather from January to December. (Presumably the weather from midnight to 1.00am is a true reflection of what has already happened in January!) Then, each hour in the afternoon can be used to forecast future weather in the reverse direction. Hence, noon to 1.00pm gives us clues for December, 1.00 to 2.00pm for November and so on. Apparently, an alternative version, used in some parts of northern Mexico, divides January 31 into 12 periods of 2 hours each, with each division corresponding to the months in reverse order.

Whatever the details, the system is said to be at least as reliable as scientific forecasts over the same time period. (Though, thinking about it, perhaps that is not that hard!)

The same cabañuelas system is used in various parts of Spain, but the annual forecast does not always begin on the same day. For instance, in Alcozar, las cabañuelas “a derechas” begin on December 13. Elsewhere in Spain, they start on August 2 or August 13. According to Divina Aparicio de Andrés, predictions in Alcozar based on las cabañuelas lasted until well into the 1940s, but their use has declined since.

See also: The origins of the cabañuelas system of weather forecasting

This is an edited version of an article originally published on MexConnect.com

The climate of Mexico is discussed, with several maps,  in chapter 4 of Geo-Mexico: the geography and dynamics of modern Mexico. Climatic hazards, such as hurricanes, droughts and floods, are looked at in detail in chapters 4 and 7. Mexico’s cultural geography and cultural landscapes are discussed in chapter 13.

Why is northern Mexico a desert region?

 Excerpts from Geo-Mexico  Comments Off on Why is northern Mexico a desert region?
Oct 102013
 

Much of northern Mexico experiences either an arid (desert) climate (less than 250 mm [10 in] of rain/year) or a semiarid (semi-desert) climate (250–750 mm [10–30 in] of rain/year). Areas with an arid (desert) climate (see map) include most of Baja California and western Sonora (together comprising the Sonoran desert), as well as the northern section of the Central Plateau (the Chihuahuan desert). These areas can experience frost and freezing during the winter.

Major climate regions in Mexico. (Fig 4-5 of Geo-Mexico, the geography and dynamics of modern Mexico). All rights reserved.

Major climate regions in Mexico. (Fig 4-5 of Geo-Mexico, the geography and dynamics of modern Mexico). All rights reserved.

Areas of semiarid (dry steppe) climate include most of the Central Plateau as well as western sections of the Western Sierra Madre, northern Yucatán and scattered inland areas as far south as Oaxaca. The rains in this region fall mostly in the summer, and localized heavy thunderstorms are quite common. The southern parts of this climatic region are warmer than the northern parts. (Mexico’s seven climate regions)

Why do parts of northern Mexico receive very little precipitation, making them deserts?

The major reason is that the zone between the Tropic of Cancer (latitude 23.5 degrees N) and latitude 30 degrees N is influenced by the Hadley Cell. This is the name given to the atmospheric circulation in tropical regions, named after George Hadley, the English amateur meteorologist who first proposed its existence, in 1735.

The Hadley Cell

The functioning of the Hadley Cell

The Hadley Cell is the driving force behind many aspects of Mexico’s weather and climate. How does it operate? Solar heating is at a maximum near the equator and diminishes towards the poles. The area near the equator is the Intertropical Convergence Zone or ITCZ (see diagram). The heating of the ITCZ makes the air there rise, leaving an area of low pressure on the surface. This low pressure sucks in air along the earth’s surface from the subtropical high pressure areas about 30 degrees N and S of the equator creating the trade winds. The trade winds pick up moisture and latent heat over the oceans before converging from either side of the equator in the ITCZ. As the air in the ITCZ rises vertically, its water vapor condenses and rain falls from the towering convective clouds. This is the ascending limb of the Hadley cell. At a height of 10–15 km above the surface, the air, now minus its moisture, returns polewards as high level anti-trade winds. Sunbathers on Mexican beaches who notice two sets of clouds above them at different heights traveling in opposite directions are witnessing the trade winds and anti-trade winds in action.

In the subtropics, this air then descends again towards the surface to complete the cell and initiates the surface trade winds again. The descending air warms up as it sinks; its relative humidity decreases, and so no precipitation occurs; hence these high pressure subtropical areas are arid. Mexico’s arid and semiarid areas coincide with the descending air segment of the Hadley Cell and these high pressure subtropical areas.

In addition, the climate of the west coast of the Baja California Peninsula is influenced by the cool Californian current, which flows towards the south. The relative humidity of the air above it drops as the current enters warmer waters, so it is not likely to bring rain to the peninsula.

The aridity of the Sonoran desert is also partly due to its position in the rain shadow of the Western Sierra Madre. The Chihuahuan desert is in an even more marked rain shadow, protected by both the Western Sierra Madre and the Eastern Sierra Madre.

Stunning stream patterns in northern Baja California

Photographer Adriana Franco from Querétaro has taken several truly stunning artistic images of stream patterns in the semi-arid region of northern Baja California (near Mexicali). The photos, taken from an ultralight, show the details of the dendritic (= tree-like) stream patterns in this region. Dendritic stream patterns are common worldwide, but these images are exceptional. In general, dendritic stream patterns are associated with relatively gentle gradients where the underlying rocks are similar throughout the drainage basin.

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Mexico’s seven climate regions

 Excerpts from Geo-Mexico  Comments Off on Mexico’s seven climate regions
Aug 152013
 

Climatologists have developed several scientific systems to classify climates. The system developed by Wladimir Köppen in the early 20th century is one of the earliest and best known. The Köppen climate classification system assumes that climate is best reflected in native vegetation and can be accurately classified using seasonal variations in temperatures and precipitation. Mexican climatologists, including Enriqueta García, have proposed minor modifications to the Köppen system to make it more appropriate for Mexico. The following paragraphs reflect García’s revised Köppen system.

Given that Mexico has many mountains with rapid changes in elevation, temperature and rainfall, applying the Köppen system, even as modified by García, to Mexico can become extremely complicated. A relatively small area of Mexico may include several Köppen climate categories. Aggregating these areas provides a less complicated, more understandable, picture of Mexico’s climates (see map). In this scheme, Mexico has seven main climate regions, as shown on the map:

Major climate regions in Mexico. (Fig 4-5 of Geo-Mexico, the geography and dynamics of modern Mexico). All rights reserved.

Major climate regions in Mexico. (Fig 4-5 of Geo-Mexico, the geography and dynamics of modern Mexico). All rights reserved.

Two tropical climates

Mexico has two tropical climates which have average temperatures of over 18°C (64°F) for all twelve months of the year.

The first, tropical wet (Af in the Köppen system, see map), has at least 60 mm (2.4 in) of rain in every month of the year. This is the climate of the Amazon and Indonesian rainforests. In Mexico this is the climate of the Gulf Coast Plain in southern Veracruz and Tabasco (classic tierra caliente areas). It also occurs in the Oaxaca and Chiapas highlands. The rains fall all year, varying from about 120–150 mm (4–5 in) in April to 380 mm (15 in) in September.

The tropical wet-and-dry (Aw) category (see the climate graph for Cancún) has a pronounced dry season. The dry winter months typically get less than 40 mm (1 in) of rain, compared to over 150 mm (6 in) in each of the summer months. Parts of West Africa, Brazil and India have a similar climate. Much of coastal Mexico, stretching from Nayarit along the Pacific coast all the way to Guatemala, is in this category. It also covers many inland areas along the Pacific coast. Central and northern Veracruz and most of the Yucatán Peninsula also have this tropical climate with summer rains.

Climate graphs for three cities. (Fig 4.6 of Geo-Mexico,)

Climate graphs for three cities. (Fig 4.6 of Geo-Mexico, the geography and dynamics of modern Mexico) All rights reserved.

Two dry climates

Areas with an arid (desert) climate (BW) usually receive less than 250 mm (10 in) of rain a year (see climate graph for Ciudad Juárez). This is the climate of the Sahara Desert and Central Australia. In Mexico dry desert areas include most of Baja California, western Sonora, and the northern section of the Central Plateau. These areas can experience frost and freezing during the winter.

Areas with the second type of arid climate, semiarid (dry steppe) (BS), receive 250–750 mm (10–30 in) of rain a year. This is the climate of the African savanna lands and much of central Asia. In Mexico, this climate region includes most of the Central Plateau as well as western sections of the Western Sierra Madre, northern Yucatán and scattered inland areas as far south as Oaxaca. The rains in this region fall mostly in the summer, and localized heavy thunderstorms are quite common. The southern parts of this climatic region are warmer than the northern parts.

Three temperate zones

Temperate climates typically have average temperatures above 10°C (50°F) in their warmest months, and a coldest month average between 3°C and 18°C (27–64°F). Moisture characteristics distinguish between the three temperate climates.

The temperate with dry winters climate (Cw) is characterized by mild temperatures, low humidity, and summer rainfall ranging from about 600 to 1200 mm (25–45 in) per year (see climate graph for Guadalajara). This is classic tierra templada country. The low nighttime temperatures in winter are typically around 5°C (41°F). Of course, higher elevations have lower temperatures with occasional frost. The highest temperatures usually reach about 35°C (95°F), though temperatures may reach as high as 40°C (104°F). This climate is similar to that of the Kenyan Highlands. In Mexico, this climate includes parts of Nuevo León and Tamaulipas, most of the Western Sierra Madre and many mountainous areas in western, central and southern Mexico. Most of the Volcanic Axis is in this temperate with dry winters zone. Here, the major control as far as temperatures are concerned is altitude, which directly affects precise rainfall amounts and seasonality, resulting in a mosaic of microclimates and natural vegetation regions.

Compared with the temperate with dry winters climate, the humid subtropical (Cf) zone gets more rainfall, is more humid and gets rain throughout the year. The only areas of Mexico with this climate are the eastern slopes of the Eastern Sierra Madre and some parts of the southern mountain systems.

The Mediterranean climate (Cs) is the mild climate associated with Europe’s Mediterranean coast as well as the California coast. The area around Tijuana is the only part of Mexico with this type of climate. This area is relatively arid and gets less than 400 mm (15 in) of rain a year; it is unique in Mexico, being the only place that is dry in summer and gets rain only in winter.

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When does it rain in Mexico?

 Excerpts from Geo-Mexico  2 Responses »
Jul 242013
 

The map below shows a regional division of Mexico by precipitation regime (the amount and seasonal distribution of precipitation). The small graph for each region shows the typical average precipitation amounts for each month of the year. (For example, region A has most precipitation in the first three or four months of the year, and very little after that). The map comes from Ernesto Jáuregai’s 1970 article about wind and water erosion in Mexico (full reference is given below).

Precipitation regimes in Mexico (Fig 2 of Jáuregai 1970)

Precipitation regimes in Mexico (Fig 2 of Jáuregai 1970)

It is clear from the map that the distribution of precipitation across Mexico is very uneven. In general the north and central plateaus are dry while the southeast receives by far the most rain. Parts of Tabasco, Northern Chiapas and Veracruz get over 4000 mm (160 in) of rain a year. This is a direct effect of the onshore north-east trade winds, which collect moisture as they cross the Gulf of Mexico and then deposit it as they reach land.

Average annual rainfall figures conceal great differences from one year to the next. In general, the variability of rainfall is indirectly proportional to the long-term average. This means that areas with low totals tend to experience high variability, greatly increasing their drought hazard.

The map also reveals that there is a marked seasonality to precipitation in almost all of Mexico, with a clear division into a wet and a dry season. Most places get almost all their rain between June and October, while January through May are dry months. Because most rainfall is in the summer months, about 71% of rainfall evaporates soon after falling. This figure can be even higher in urban areas. Only about 26% runs off into rivers and lakes, and 3% seeps down to recharge subterranean aquifers.

One apparent anomaly to the pattern shown on the map is that the extreme north-west corner of Baja California (region A) has a Mediterranean climate where summers are dry and most rain falls in winter. Elsewhere in Mexico winter months are relatively dry. Southern and central Mexico have markedly dry winters, receiving less than 5% of their annual precipitation totals in the first three months of the year. The northern half of Mexico and the eastern coastal strip, including the Yucatán peninsula, have slightly more balanced precipitation, receiving between 5 and 18% of annual totals between January and March.

Map reference:

Ernesto Jáuregai. 1970. “La erosión hidráulica y eólica en México y sus efectos en las estructuras hidráulicas y en los núcleos de población.” UNAM: Boletín del Instituto de Geografía, Vol III, pp 39-60.

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The three main causes of precipitation in Mexico

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Jul 222013
 

The three basic types of rainfall (convectional, orographic and cyclonic) all play a role in determining the amount and timing of precipitation in Mexico.

Why does it rain?

In Mexico, most precipitation falls as rain, though snowfalls are not uncommon in parts of northern Mexico or at the highest elevations where air temperatures are cooler. For precipitation to occur, the air must first acquire moisture. Warm air absorbs water through evaporation from nearby bodies of water and through evapotranspiration from plants. The amount of water the air holds compared to the maximum amount it can hold at that temperature is the relative humidity. If warm moist air rises, it will cool. As it cools, its relative humidity rises. If relative humidity reaches 100% and condensation nuclei (particles such as dust or contaminants) are present, then water vapor will condense out of the air to form clouds. As clouds develop, water molecules coalesce until individual drops are heavy enough to fall out of the cloud as precipitation. Ice crystals fall as snow, water falls as raindrops, frozen ice pellets fall as hail.

For precipitation to occur, the weight of the individual drops must be sufficient for the effects of gravity to overcome the upwards thrust of the surrounding air. In very unstable conditions where air is rising rapidly, individual raindrops must become much larger before they can fall out of the cloud. The largest raindrops will have traveled up and down inside the cloud repeatedly, gaining size, before they finally fall to the ground. The same principle applies to hailstorms which gather an additional layer of ice for every trip they make inside the cloud before falling.

Though Mexico is considered to be relatively arid, the country as a whole receives an average of about 760 mm (30 in) of rain per year. This is a considerable amount of precipitation, almost exactly the same amount as Toronto, and considerably more than the average for either Canada or the USA.

Annual precipitation in Mexico (Fig .4.3 of Geo-Mexico)

Annual precipitation in Mexico (Fig .4.3 of Geo-Mexico, the geography and dynamics of modern Mexico) All rights reserved.

The three main causes of precipitation in Mexico

Convectional rain is associated with hot afternoons. During the morning, warm air near the surface collects great quantities of moisture. As temperatures increase towards mid-day, pockets of moist warm air are sent upwards, quickly leading to condensation and clouds. As the clouds continue to rise, they cool to the point where precipitation becomes inevitable. Afternoon and evening rain showers result, often heavy and accompanied by thunder and lightening. Convectional rain occurs throughout Mexico but is a summer phenomenon since this is the time of year when solar radiation and ground heating is at a maximum. The effects of convectional rain are enhanced by the presence at that time of year over southern Mexico of the Intertropical Convergence Zone, a broad belt of generally rising air which migrates seasonally either side of the equator.

Orographic rainfall, the second type of rainfall, is associated with mountains. Mountains block the movement of clouds and force them to rise. This has a profound impact on precipitation. As the clouds rise, further condensation occurs and precipitation becomes extremely likely, as they cool to the point where they can no longer hold their moisture. Therefore, it rains a great deal on the windward or wet side of the range. By the time the air passes over the mountain range to the other side, it has lost much of its moisture. As it descends, it warms up and its relative humidity falls, so that there is little chance of any precipitation on the leeward side, known as the rain shadow.

For example, the summer north-east trade winds blow moist clouds from the Gulf of Mexico towards the Southern Sierra Madre and Chiapas Highlands. The eastern side of these mountains receives heavy rainfall. The mountain slopes in central Veracruz, eastern Oaxaca and parts of Chiapas have about 150 cloudy days and get about 2000 mm (80 in) of rain a year. However, the western slopes get only half as much rain and have only 90 cloudy days a year. Orographic precipitation sets virtually all the rainfall and snowfall records, even more than hurricanes. Tenango, Oaxaca is the rainiest place in Mexico; it receives about 5000 mm (16.4 ft) of rain each year. The orientation of mountain ranges is therefore critical to understanding precipitation patterns. The differences between windward and leeward sides of a mountain range can be very dramatic. For instance, El Chico and Pachuca in the state of Hidalgo are only 10 km apart but have 1500 and 400 mm of precipitation respectively each year.

The third type of rainfall is called cyclonic or frontal precipitation. This is the form of precipitation brought by the mid-latitude storms known as nortes, and the tropical storms that sometimes evolve into hurricanes. Nortes occur when the polar air behind a cold front displaces the warmer surface air, forcing it to rise as the cool air pushes its way underneath. At the surface, a sudden drop in temperature and the advent of cold winds marks the passage of the front, followed by several days of overcast skies with light rains or drizzle, onomatopoeically called chipichipis in some areas of Mexico.

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The geography of droughts in Mexico

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Jun 172013
 

Today (June 17) is the UN’s “World Day to Combat Desertification and Drought.”

How does Mexico stand right now in relation to drought? Drought currently affects about 40% of the country (see map). Some parts of northern Mexico have been experiencing a severe drought for almost three years. The worst affected states are Chihuahua, Nuevo León, Coahuila, Durango, Zacatecas, Tamaulipas, San Luis Potosí, together with parts of Querétaro, Aguascalientes, Sinaloa and Sonora.

Areas suffering from short-term and long-term drought, April 2013. Click map to enlarge.

Areas suffering from short-term and long-term drought, April 2013. Click map to enlarge.

Last year’s rains did reduce the area suffering from drought from 55.9% of Mexico to 38.6%, but that figure has risen to well over 40% this year.

In 2012, and earlier this year, many major cities, including Mexico City and Guadalajara, had to enforce water rationing for several months, supplying water to individual households only on certain days each week.

As this year’s rainy season begins in central Mexico, dozens of reservoirs are at critically low levels. Reservoirs in Coahuila average only 10% of their capacity, only slightly better than those in San Luis Potosí (12%). Even the populous state of Jalisco faces problems; its reservoirs are at 27% of capacity.

Things are unlikely to improve any time soon since the current long range forecast for this rainy season is for 30% less precipitation than the long term average.

The drought has already caused significant losses to farmers. Livestock owners in northern Mexico have culled herds and are having to buy in supplies of water to top up their private wells. Rainfall so far in 2013 has been well below long-term averages in central and northern Mexico, which may limit the region’s productivity of rain-fed agriculture (mostly wheat, corn, sorghum and other fodder crops).

Authorities at the three levels of government (federal, state and municipal) in many regions are calling for urgent concerted action to help farmers as well as to ensure supplies of drinking water to towns, cities and rural communities.

In Tamaulipas, at least 60 rural communities are confronting a critical water shortage. Farming representatives argue that while the National Water Commission (Conagua) has guaranteed water supply for urban areas, many rural areas remain vulnerable, and lack both potable water and food support on account of harvest failures due to lack of rain. In Tamaulipas alone, drought has affected 22,000 hectares and killed 800 head of livestock in the past year.

In Nuevo León, citrus farmers fear that their harvest, which begins in October will be 40-50% lower than usual. The state government is supporting a 35-million-dollar support program for farmers which includes supplying water by truck, rehabilitating deep wells and offering subsidies for water that farmers buy direct from private suppliers. The spring harvest in Nuevo León was lost completely, and a “severe drought emergency” has been declared in at least 14 municiapliites (Allende, Cadereyta, Dr. Arroyo, General Terán, Higueras, Juárez, Lampazos, Rayones, Sabinas Hidalgo, Santa Catarina, Villaldama, Hidalgo, García and Mina) allowing them access to federal aid.

Besides loss of livestock and crops, the prolonged drought in Mexico is having many other effects, which include:

Migration – In Durango state, more than 1500 Mennonites have left their homes due to the drought, according to Mennonite leader Enrique Peter Klassen, with some of the migrants headed for neighboring state of Chihuahua and others emigrating to Canada.

Wildfires – The first four months of 2013 was the third worst season for forest fires (more than 7000 were reported) in recent history, after 1996 and 2011. According to the National Forestry Commission (Conafor), wildfires ravaged 170,000 hectares, mostly grassland and wooded pastureland, in the first four months of this year. The states which suffered most were Oaxaca (21,000 ha), Baja California Sur (16,000), Guerrero (13,857) and Jalisco (13,697).

Lake Chapala – In the past two years, the level of Mexico’s largest natural lake, Lake Chapala, has once again fallen to crisis levels. (The lake has a long history of fluctuations in level, discussed in detail in our Geo-Mexico, the geography and dynamics of modern Mexico). The lake currently holds 2.84 million cubic meters of water, about 36% of its capacity. Its level has fallen 1.43 meters since last year’s rainy season, the lake’s most dramatic decline for 20 years. The rainy seasons in 2011 and 2012 raised the lake level by only 24 cm and 50 cm respectively, so unless this year’s rains are exceptionally heavy, the lake will continue to drop.

Previous posts related to drought:

Hurricane names and forecast for 2013

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May 112013
 

The 2013 hurricane season in Mexico is underway. The “official” hurricane season is from 15 May to 30 November each year for Pacific coast storms, and from 1 June to 30 November for Atlantic storms, though most hurricane activity is concentrated in the months from July to September. Hurricanes are also known as typhoons or tropical cyclones.

The table shows the World Meteorological Organization’s official list of 2012 hurricane names. Note that male and female names alternate. Names are often reused in future years, with the exception of the names of any particularly violent storms, which are officially “retired” from the list for a long time.

2013 Hurricane Names for the Atlantic, Gulf of Mexico and Caribbean
AndreaGabrielleLorenzoRebekah
BarryHumbertoMelissaSebastien
ChantalIngridNestorTanya
DorianJerryOlgaVan
ErinKarenPabloWendy
Ferdinand

2013 Hurricane Names for the Eastern Pacific
AlvinGilManuelTico
BarbaraHenrietteNardaVelma
CosmeIvoOctaveWallis
DalilaJuliettePriscillaXina
ErickKikoRaymondYork
FlossieLorenaSoniaZelda

In their early season forecast for this year, Philip Klotzbach and William Gray, researchers at Colorado State University,  expect hurricane activity in the Atlantic to be significantly higher than the 1981-2010 average. They write that, “The tropical Atlantic has anomalously warmed over the past several months, and it appears that the chances of an El Niño event this summer and fall are unlikely”. (A strong el Niño is likely to minimize Atlantic hurricane activity). They predict that in the 2013 season 18 named storms will form in the Atlantic: 9 tropical storms, 5 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 4 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). These forecasts will be updated on 3 June and 2 August.

saffir-simpson-scale

For the Pacific coast, Mexico’s National Meteorological Service (Servicio Metrológico Nacional, SMN) is expecting 14 named storms: 6 tropical storms, 4 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 4 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). The SNM publishes regular updates on hurricane activity (in Spanish) on its webpage and via its Twitter account: @huracanconagua.

How accurate was the forecast in 2012?

The late season (3 August) prediction for 2012 (last year) was for 14 named storms in the Atlantic: 8 tropical storms, 4 moderate hurricanes and 2 severe hurricanes. In reality, the 2012 Atlantic season had 19 named storms: 9 tropical storms, 8 moderate hurricanes and 2 severe hurricanes.

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What is the elevation of Mexico’s cities?

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Feb 042013
 

The short answer to “What is the elevation of Mexico’s cities?” is “somewhere between zero and 3000 meters (8200 ft) above sea level!” Mexico’s extraordinarily varied relief provides settlement opportunities at a very wide range of elevations. Many Mexican cities are at or near sea level. This group includes not only coastal resort cities such as Acapulco, Cancún and Puerto Vallarta, but also Tijuana on the northern border and, at the opposite end of the country, Mérida, the inland capital of Yucatán state.

Mexico City, the nation’s capital, has an average elevation of about 2250 meters (7400 ft.), similar to that of nearby Puebla. Toluca, the capital city of the state of México, is almost 400 m higher, while both Huixquilucan and Zinacantepec (also in the state of México) are at an elevation of over 2700 meters. Moving northwards from Mexico City, numerous major cities are at elevations of between 1500 meters and 1850 meters above sea level. The cities nearer the lower end of this range include Saltillo, Oaxaca and Guadalajara, while Aguascalientes, Querétaro, Guanajuato, Morelia and León are all situated at elevations close to 1800 meters.

Frequency plot of city elevations in Mexico. Credit: Geo-Mexico

Frequency plot of city elevations in Mexico. Credit: Geo-Mexico

Are there more cities at some elevations than others? Each dot on the graph above represents one of Mexico’s 170 largest cities and towns, plotted against its average elevation. The two major clusters of cities occur at elevations of close to sea level and at 2250 meters, with another smaller, more spread out cluster between 1500 meters and 2000 meters. Perhaps somewhat surprisingly, there are relatively few Mexican cities at elevations of between 100 and 1500 meters (4920 ft.).

  • Q. Can you suggest any reasons for this? [Hint: Look at a relief map of Mexico to see how much land surface there actually is at different elevations].

The graph also shows the division of Mexico’s climate and vegetation zones by elevation first proposed by Alexander von Humbuldt following his visit to Mexico in 1803–1804. The terms tierra caliente, tierra templada, and tierra fría are still widely used by non-specialists today to describe the vertical differentiation of Mexico’s climatic and vegetation zones (see cross-section below).

Altitude zones

Altitude zones. Copyright John Wiley & Sons Inc. 2000.

The tierra caliente (hot land) includes all areas under about 900 m (3000 ft). These areas generally have a mean annual temperature above 25°C (77°F). Their natural vegetation is usually either tropical evergreen or tropical deciduous forest. Farms produce tropical crops such as sugar-cane, cacao and bananas. Tierra templada (temperate land) describes the area between 900 and 1800 m (3000 to 6000 ft) where mean annual temperatures are usually between about 18°C and 25°C (64°F to 77°F). The natural vegetation in these zones is temperate forest, such as oak and pine-oak forest. Farms grow crops such as corn (maize), beans, squash, wheat and coffee. Tierra fria (cold land) is over 1800 m (6000 ft) where mean annual temperatures are in the range 13°–18°C (55°–64°F). At these altitudes pine and pine-fir forests are common. Farm crops include barley and potatoes. On the highest mountain tops, above the tierra fría is tierra helada, frosty land.

Interestingly, the tierra templada appears to have fewer cities than might be expected. Equally, while archaeologists have sometimes argued for the advantages of siting settlements close to the transition zone between climates, where a variety of produce from very distinct climates might be traded, the graph shows no evidence for this.

It would be misleading to read too much into this superficial analysis of the elevations of Mexican settlements. First, we have only considered the 170 largest settlements. Second, an individual settlement may extend over a range of elevation, so using an average figure does not reveal the entire picture. Thirdly, the precise elevations for tierra caliente, templada and fria all depend on the latitude and other local factors. Even so, it might be interesting to extend this analysis at some future time to include far more settlements to see if the patterns identified are still present or if others emerge.

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How accurate was last year’s hurricane prediction?

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Jan 162012
 

The annual prediction of the hurricane activity on the Atlantic/Gulf/Caribbean side of Mexico for 2011 by Dr Philip Klotzbach and Dr. William Gray (Colorado State University) was for a slightly more active season than in 2010. For 2011, they introduced some modifications to their predictive model, which now takes into account:

  • Predictor 1. Gradient of sea surface temperatures (SST) in February-March between the Eastern Subtropical region of the Atlantic and the South Atlantic. This has a positive connection with hurricane activity.
  • Predictor 2. Air pressure at sea level in March in the Subtropical Atlantic. This has a negative connection with hurricane activity.
  • Predictor 3. Air pressure at sea level in February in the South-Eastern Pacific. This new variable has a positive connection with hurricane activity.
  • Predictor 4. Forecast made in March from Central Europe for sea surface temperatures in September for the El Niño-3 region. This new predictor has a negative connection with hurricane activity.
Tracks of Atlantic Hurricanes, 2011

Tracks of Atlantic Hurricanes, 2011

In April, the prediction for the 2011 Atlantic/Caribbean hurricane season was for 16 tropical cyclones, including 7 tropical storms, 4 moderate hurricanes (Category 1 or 2 on the Saffir-Simpson scale) and 5 strong hurricanes (C 3, 4 or 5).

This prediction proved to be quite good. In the event, there were actually 19 tropical cyclones, including 12 tropical storms, 4 moderate hurricanes (C1, C2) and 3 strong hurricanes (one C3 and two C4).

Tracks of Pacific Hurricanes, 2011

Tracks of Pacific Hurricanes, 2011

On the Pacific coast, the 2011 season saw 11 tropical cyclones including 1 tropical storm, 4 moderate hurricanes and 6 strong hurricanes. Fortunately, almost all these cyclones remained out at sea and only Hurricane Jova, which reached category 3 in early October, caused any significant damage on land (see Hurricane Jova smashes into Barra de Navidad and Melaque on Mexico’s Pacific Coast).

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The changing climate of Mexico’s urban areas

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Dec 312011
 

As large urban areas grow in size, they change their local climate in various ways. The best known effect is that called the urban heat island: the air above cities is significantly warmer than the surrounding air in suburban and rural areas. The transfer of heat energy from people, homes, vehicles and factories warms the air immediately above the city. The irregular built-up surfaces of a city absorb more energy than nearby vegetated areas, also helping to raise the city’s temperature. The difference in temperature is most noticeable just before sunrise.

Wind speeds in cities tend to be lower than in their rural outskirts. Precipitation tends to be slightly higher, as a result of the additional heat energy, which causes mid-afternoon instability, and because city air has higher concentrations of particulates (dust, smog, contaminants) from vehicles and factories.

Urban heat island (°C) in Puebla, Mexico

Urban heat island (°C) in Puebla, Mexico, 2200 h, 11 November 1970 (Source: G.M. Gäb, 1976)

Mexican cities are no exception. The urban heat island differential has risen by an average of 0.44ºC per decade for large cities (population over one million), and by 0.37ºC per decade for mid-sized cities (population between 150,000 and 1,000,000). These rates are clearly greater than the background effect of global warming, variously estimated at between 0.07 and 0.20ºC a decade.

There is no doubt that accelerated urbanization has warmed and is continuing to warm urban air, affecting the comfort levels of millions of people. The cities where urban temperatures have risen most rapidly are Torreón, which warmed at a rate of 1.2ºC per decade from 1952–1998, and Guadalajara, where temperatures rose by 0.74ºC a decade from 1920–1997. [Jauregui, E. 2005. Impact of Increasing Urbanization on the Thermal Climate of Large Mexican Cities]

The case of Mexico City shows an additional complication. At the end of the 19th century, comparing minimum temperatures, Mexico City (population then 400,000) was about 1.5ºC warmer than surrounding areas. This difference had risen dramatically to about 9ºC (16ºF) by the 1980s. Urbanization has certainly played a part, and its effects have perhaps been exacerbated by the city’s unfortunate position in a basin, which traps air, heat and contamination. However, climate modeling suggests that the loss of lakes in the Valley of Mexico, including the draining of most of Lake Texcoco, has played at least as large a part in Mexico City’s increased temperatures as the expansion of its urban area. [Jazcilevich, A. et al. 2000. Simulated Urban Climate Response to Historical Land Use Modification in the Basin of Mexico. Climatic Change 44]

In addition, the incidence of intense rain showers (those where more than 20 mm (0.8 in) falls per hour) in Mexico City has also risen steadily, from four a decade in the 1940s to twenty a decade in 1980s. There is, however, no convincing evidence that wet season rainfall totals have increased, despite the combination of increased temperatures and instability, and the higher number of particulates in the air from dust, vehicle exhausts and factories. Away from the edge of the city, precipitation appears to have declined. [Jauregui, E. 2004. Impact of land-use changes on the climate of the Mexico City Region. Mexico City: Boletín del Instituto de Geografía.]

In summary, the expansion of Mexico City appears to have led to warmer, drier conditions in the Valley of Mexico.

Urban areas also have distinctive effects on hydrology. The roads and buildings of cities form impermeable surfaces which reduce infiltration almost to zero and greatly increase surface runoff. The lag time between a rainstorm and peak discharge in stream channels is much less in urban areas than in their rural surroundings. This makes the likelihood of flooding much greater in urban areas. In most cities, surface runoff is channeled rapidly into gutters and drains (a form of high speed throughflow) in an effort to reduce flood risk.

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Mexico’s 2011 drought is raising the price of basic foodstuffs

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Dec 052011
 

This year’s drought – see Many states in Mexico badly affected by drought – is now widely viewed as the worst to occur since modern record-keeping for precipitation began about 80 years ago.

Short-term droughts are not unusual in Mexico. As the graph shows, there is a clear cyclical pattern to the timing of short-term droughts in Mexico. This is because most of the country receives almost all its annual precipitation in just a few months, from May or June (depending on precise location) to September-October.

The scale of the current drought is readily apparent from the graph. This year, far more of the country is affected, and the level of drought is far more severe.

Seasonal drought in Mexico, 2003-2012
Seasonal drought in Mexico, 2003-2012. Click to enlarge.

The drought is having numerous adverse impacts

It is already having an effect on food prices. Several of the basic foodstuffs  making up Mexico’s basic basket of goods for economic indices such as the inflation index, have risen sharply in price in recent months. A shortage of corn has led to a 70% increase in imports of yellow corn from the USA.

Incredibly, Mexico, the home of corn, is now the world’s second largest importer. Corn, as we have noted in previous posts, is a vital ingredient in Mexican cuisine, and is particularly important in the southern half of the country, especially in the more rural and indigenous areas. The shortage of corn has led to a rise in the price of tortillas, a dietary staple in almost all of the country. Tortilla prices have risen up to 18%, many times Mexico’s overall inflation rate of about 3.5%.

The production of chiles, another staple of the Mexican diet, has also fallen due to the drought, by an estimated 40%. In Zacatecas, that state’s 2,500 chile-growers will have produced 120,000 tons of green chile and 62,150 tons of dried chile this year, even though they have only been able to harvest chiles twice this year, rather than the normal four times. The state is the leading source of dried chile in Mexico. The area cultivated for chiles in Zacatecas has also fallen this year, to 31,300 hectares. The decrease in production has had a direct impact on the number of harvesting jobs available, since each hectare of chile cultivation usually means 150 seasonal jobs. The production shortage for chiles will be offset by more imports from Peru and China.

At latest count, 770 municipalities are now suffering from drought, and at least 2.5 million people in 1500 communities are left with insufficient drinking water. In the state of Durango alone, more than one million people are currently experiencing extreme drought, and 149 communities are completely without drinking water.

The long-term outlook is not favorable for these areas since climate change is expected to increase both the frequency and severity of droughts over the next twenty to thirty years.

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An enchanted lake in Veracruz rises every dry season but falls every rainy season

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Jun 092011
 

Peculiar, but true. There are several lakes named Laguna Encantada (Enchanted Lake) in Mexico, but this one is near Catemaco in the Tuxtlas region of the state of Veracruz. Catemaco is famous for its witches, so perhaps one of them cast a spell on the lake, making it behave perversely, its level changing in opposition to all the other lakes in the country?

Laguna Encantada

Laguna Encantada, Veracruz. Photo credit: Hector Reyes

Occupying the crater of an extinct volcano, La Laguna Encantada is a truly beautiful lake, especially near sunrise or sunset. Laguna Encantada is located 3 km northeast of San Andrés Tuxtla. The access road is unpaved. The views are ever-changing on the easy walk of about 1500 meters (slightly under one mile) around its shoreline. As you walk, try counting the butterflies. A study twenty years ago recorded a staggering total of 182 different species in this relatively small area of jungle.

The lake nestles on the southern flank of the San Martín volcano. This dormant volcano is a prominent landmark north-west of Lake Catemaco close to San Andrés Tuxtla. Its crater, 1500 meters across, is at a height of about 1400 meters above sea level, and has two small subsidiary cones inside it.

The basaltic lavas and layers of ash forming the volcano are highly permeable and porous. As a result, despite the heavy rainfall, there are no permanent streams flowing down the upper slopes.

Some distance away from the volcano, though, there are several good-sized lakes including Catemaco and Laguna Encantada. Catemaco is large enough to capture plenty of rainfall to maintain its level. The much smaller basin holding Laguna Encantada (350 meters above sea level), however, does not receive sufficient rain to keep its level high.

Instead, and this is the wonder of La Laguna Encantada, much of its water supply comes from underground. Water that falls on the slopes of the San Martín volcano during the rainy season soaks into the ground and then percolates slowly towards the lake, so slowly that it takes six months to reach it. The result? The lake is unable to sustain its level during the rainy season, but the underground water reaching it in the dry season is more than sufficient to replenish its level. Maybe the witches of Catemaco have something to do with it, but hydrology also plays a part!

Eyipantla Falls

Eyipantla Falls Photo: Tony Burton

Salto de Eyipantla

Only a few kilometers from Laguna Encantada is another wonderful natural sight: the Eyipantla Waterfall (Salto de Eyipantla). The water for the falls comes from the Comoapan river, which drains Lake Catemaco. After heavy rain, the curtain of water at Eyipantla is about 50 meters high and 20 meters wide. The sunlight playing on the water creates a dazzling display of magical colors. The Tuxtlas region has been the setting for numerous movies and commercials and the impressive Eyipantla Falls have starred in many of them. The unusual name, Eyipantla, reflects its three chutes of water, and is derived from the Nahuátl words, eyi (three), pantli (trench) and tla (water).

Chapter 4 of Geo-Mexico: the geography and dynamics of modern Mexico discusses Mexico’s diverse climates.  Chapter 5 focuses on ecosystems and biodiversity.  Chapter 30 analyzes environmental issues and trends including the impact of Old World species imported by the Spaniards, current environmental threats, and efforts to protect the environment.  Buy your copy today to have a handy reference guide to all major aspects of Mexico’s geography!

Atlantic and eastern Pacific hurricane names for 2011

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Apr 132011
 

Hurricanes are also known as typhoons or tropical cyclones. The table shows the World Meteorological Organization’s official list of 2011 hurricane names. Note that male and female names alternate. Names are often reused in future years, with the exception of the names of any particularly violent storms, which are officially “retired” from the list for a long time.

Atlantic, Gulf of Mexico and CaribbeanEastern Pacific
ArleneAdrian
BretBeatrix
CindyCalvin
DonDora
EmilyEugene
FranklinFernanda
GertGreg
HarveyHilary
IreneIrwin
JoseJova
KatiaKenneth
LeeLidia
MariaMax
NateNorma
OpheliaOtis
PhilippePilar
RinaRamon
SeanSelma
TammyTodd
VanceVeronica
WhitneyWiley
Xina
York
Zelda

In Mexico, the “official” hurricane season is from May 15 to November 30 each year for Pacific coast storms, and from June 1 to Novemebr 30 for Atlantic storms, though most hurricane activity is concentrated in the months from July to September.

This year, Philip Klotzbach and William Gray, researchers at Colorado State University, predict that 16 named storms will form in the Atlantic: 7 tropical storms,4 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 5 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale).

For the Pacific coast, Mexico’s National Meteorological Service (Servicio Metrológico Nacional, SMN) is expecting 17 storms: 7  tropical storms, 6 moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 4 severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale). The SNM publishes regular updates on hurricane activity (in Spanish) on its webpage and via its Twitter account: @huracanconagua.

Previous posts related to hurricane prediction:

Hurricanes and other climatic hazards are analyzed in detail in chapter 4 of  Geo-Mexico: the geography and dynamics of modern Mexico.

How do El Niño events affect Mexico?

 Excerpts from Geo-Mexico  Comments Off on How do El Niño events affect Mexico?
Apr 112011
 

La Niña and El Niño are two major periodic disturbances to the normal oceanic and atmospheric circulation patterns over the Pacific Ocean which have widespread effects around the world. The normal circulation in the equatorial Pacific (the Walker circulation cell) results from a low pressure area over the western Pacific (due to warm surface ocean temperatures) and a high pressure area over the eastern Pacific (due to the upwelling of cold ocean water off the coast of Ecuador). Surface trade winds blow from east to west, while high altitude air flow is from west to east.

A La Niña event is an intensification of the normal Walker cell. This results in warmer and drier conditions than normal, rarely with serious consequences for Mexico.

However, during an El Niño Southern Oscillation (ENSO) event, the Walker circulation pattern is essentially reversed. Early in the year, warm ocean water extends much further east, causing warm moist air to rise off the coast of South and Central America, bringing heavy rainfall to areas along the west coast of Mexico. The El Niño in 1998 raised the temperature of water off Mexico’s Pacific coast by some 3° to 5°C (6° to 9°F) and also increased the humidity considerably. Historically, ENSO events have occurred every four to seven years, but their frequency may now be increasing.

The effects of an ENSO event are also felt on the Gulf coast. The low pressure area resulting from the air rising off the western coast causes air from further east to be dragged across Mexico. This means that more cold fronts or nortes enter north and central Mexico. Winter precipitation in these areas increases significantly, especially in the north, and temperatures are much cooler than usual. Flooding can result in coastal areas. ENSO effects are also felt in other parts of the world.

In Mexico, ENSO events not only affect winter precipitation but also summer precipitation, which is more critical for farmers. This is because they push the equatorial Intertropical Convergence Zone (ITCZ), where the north-east and south-east trade winds meet, further south. This reduces the convective activity and rainfall in Mexico’s central highlands. Furthermore, this may reduce cloud cover and therefore increase solar radiation and evapotranspiration, making the ground even drier.

In summary, subsistence corn (maize) farmers find that their cooler, wetter winter than normal is immediately followed by a hotter and drier summer growing season. This can have disastrous consequences for their food security. The rapid onset of changed conditions does not allow much time for adequate adjustments to be made to their choice of crops or farming methods.

Historical analysis combined with greater climatological understanding shows that many of the worst droughts and floods in Mexico have been associated with either ENSO events or with the related Pacific-North American Oscillation. Perhaps 65% of the variability of Mexican climate results from changes in these large-scale circulations.

The naughty nortes of Mexico

 Excerpts from Geo-Mexico  Comments Off on The naughty nortes of Mexico
Mar 292011
 

Mid-latitude storms known as nortes (northers) disturb the normal weather patterns up to 20 times a year during winter, from November to March. They occur when northern polar air moves south into northern and central Mexico.

They bring low pressure (cyclonic) conditions, heralded by the arrival of a cold front. The polar air displaces the warmer surface air, forcing it to rise as the cool air pushes its way underneath. At the surface, a sudden drop in temperature and the advent of cold winds marks the passage of the front, followed by several days of overcast skies with light rains or drizzle, onomatopoeically called chipichipis in some areas.

Rains from nortes are heavier on the northern or eastern sides of mountains where the cool air is forced to rise. As the front passes, the temperature can drop by 5–8 degrees C (9–14 degrees F) in a few hours.

From an agricultural perspective these rains are a welcome sight for farmers, helping to improve grazing land and reduce the chances of wind-blown soil erosion. However, the winds can play havoc with shipping in the Gulf of Mexico and result in ports being temporarily closed. Veracruz and Tampico are regularly affected.

Where is the best place in Mexico to celebrate the Spring Equinox?

 Other  Comments Off on Where is the best place in Mexico to celebrate the Spring Equinox?
Mar 202011
 

The main pyramid at the Maya site of Chichen Itza in the Yucatán Peninsula is the most popular site in Mexico for crowds to gather and celebrate the Spring Equinox (March 20-21). The Maya were accomplished astronomers and were able to accurately predict equinoxes, eclipses and other celestial events hundreds of years in advance.

Crowds gather to witness the serpent descend the pyramid
Crowds gather to witness the serpent descend the pyramid. Original upload by shawn_christie1970 (Flickr).

The main pyramid at Chichen Itza, known as the Pyramid of Kukulkan, has some unusual properties which researchers are still trying to explain. It is so precisely aligned that for a day or two either side of the Spring Equinox, the light falling on one side of the pyramid creates undulating shadows that look like a serpent slithering down the pyramid steps. The effect is best seen between 4 and 5 pm.

The slithering serpent is not the only surprise that the Pyramid of Kukulkan has in store for visitors. Kukulkan was a Mayan deity, the “feathered serpent”, more usually known in central Mexico as Quetzalcoatl. The Pyramid of Kukulkan is linked to the quetzal bird, because depictions of Kukulkan often show the distinctively long feathers of the quetzal. Standing in front of the pyramid and making a single hand clap results in an echo from the pyramid’s staircase, an echo which sounds like the downward chirp of a quetzal bird.

David Lubman has proposed that this may be the earliest sound recording so far discovered anywhere on the planet. We may never know whether it was originally accidental or intentional, but Lubman makes a strong case for this chirp being a deliberate representation of the call of the Respendant Quetzal bird, a bird described in Peterson and Chalif’s Field Guide to Mexican Birds as “the most spectacular bird in the New World.” Quetzal birds were sacred to the Maya, and their feathers were highly prized; the birds were formerly common in the rainforest which originally cloaked this entire region.

Sources

Original article on MexConnect.com: Did you know? Mayan architects built world’s oldest sound recordings

Lubman, David (1998) “Archaeological acoustic study of chirped echo from the Mayan pyramid at Chichen Itza, in the Yucatan Region of Mexico… Is this the world’s oldest known sound recording?“. Paper presented to the 136th Meeting of the Acoustical Society of America, October 1998.

Lubman, David (2002) “More on the Mayan Pyramid“. Article on the website of the Orange County Regional Chapter of the Acoustical Society of America:

Mexican geophysicists develop new model for hurricane forecasting

 Mexico's geography in the Press  Comments Off on Mexican geophysicists develop new model for hurricane forecasting
Jan 112011
 

The new methods, using physics rather than mathematics as the basis, can be used to forecast the timing of Category 5 hurricanes, the most severe level on the Saffir-Simpson scale.

Category 5 hurricanes have sustained wind speeds of up to 250 km/hr, with catastrophic impacts on homes, lives and infrastructure. The most recent Category 5 hurricanes to strike Mexico are Dean (2007), Wilma (2005), Mitch (1998), Gilbert (1988) and Beulah (1967).

Scientists at the Geophysics Institute of the National University (UNAM) in Mexico City have developed a physics-based model, relying on three-dimensional imaging, which can be used to predict severe (Category 5) hurricanes. They have also pin-pointed precisely where in the deep waters of the Atlantic Ocean severe hurricanes are most likely to originate. The scientists conclude that severe hurricanes do not occur randomly in time, but tend to occur at roughly cyclical intervals, about every ten years.

Diagram showing features of the existing GFDL Hurricane Prediction System

Diagram showing features of the existing GFDL Hurricane Prediction System

They hope that the new techniques will improve the forecasting associated with these severe weather hazards, and offer more lead-in time for the updating and implementation of evacuation plans and other mitigation measures.

Lead investigator Víctor Manuel Velasco Herrera says that, according to the model, the next period when Category 5 hurricanes will occur will begin in 2013 and end in 2017, “with a margin of error of one year.”

Watch this space for updates in due course!

Previous posts related to hurricane prediction:

Hurricanes and other climatological phenomena are analyzed in chapters 4 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico. Buy your copy today, so you have a handy reference guide available whenever you need it.

Dust, snowmelt and the reduced flow of the Colorado River into Mexico

 Other  Comments Off on Dust, snowmelt and the reduced flow of the Colorado River into Mexico
Oct 262010
 

The Colorado River flows almost entirely in the USA, though its extensive delta is in Baja California. The USA and Mexico have negotiated usage rights designed to guarantee a minimum flow reaching Mexico and to safeguard the water available for numerous cities in the USA that depend on water from the Colorado, and for the rapidly-growing urban centers of Mexicali, Tijuana, Tecate and Rosarito in Baja California.

Even so, the amount of water reaching Mexico has declined dramatically as a result of the Hoover and Glen Canyon dams and other diversions of Colorado River water in the USA. The Colorado River delta has been almost totally dry for most of the last decade.

A new study led by a NASA scientist, links increased human activity in the USA over the past 150 years to earlier annual snowmelt in the Rocky Mountains and reduced flow rates in the Colorado River.

According to the study:

  • lake sediments reveal that between 5 and 6 times as much dust now falls on the Rocky Mountains as 150 years ago – an increase attributed to soil disturbances caused by agriculture and grazing
  • dust settling on snow makes the surface darker, enabling it to absorb more incoming solar energy (ie. the dust changes the albedo of the surface)
  • this increased absorption of solar energy causes earlier snowmelt and more evaporation to enter the atmosphere – peak spring runoff now comes three weeks earlier than 150 years ago
  • this earlier snowmelt exposes vegetation, causing plants to lose more water to the atmosphere than previously – this loss is estimated at almost 1 billion cubic meters (35 billion cubic feet) of water each year
  • this loss of water causes river discharges to be lower than previously; the annual runoff averages less than 95% of the levels found prior to extensive human settlement
  • earlier snowmelt leads to earlier peak runoff into rivers. This complicates water management, especially during the summer.

How much is 1 billion cubic meters of water?

  • sufficient to meet the demands of the entire city of Los Angeles for 18 months
  • more than 50% of the amount of water guaranteed to enter Mexico each year via the Colorado by a 1944 USA-Mexico treaty
  • about 14% of the current volume of Lake Chapala, Mexico’s largest natural lake

How can the situation be reversed/ameliorated?

One successful strategy, mentioned in the article, has been the Taylor Grazing Act (1934). This has improved conditions on public grazing lands, decreasing the amount of dustfall in the Rockies by about 25%. Other strategies are needed since climate change may well exacerbate the effects the additional dust has had on river flows.

Related posts:

Rivers, reservoirs and water-related issues are discussed in chapters 6 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico. Ask your library to buy a copy of this handy reference guide to all aspects of Mexico’s geography today! Better yet, order your own copy…

The 10 warmest states in Mexico

 Maps, Teaching ideas  Comments Off on The 10 warmest states in Mexico
Jul 292010
 

The table shows the ten warmest states in Mexico, defined by their average annual temperature.

RankStateAverage annual temperature (degrees C)
1Tabasco26.4
2Yucatán25.9
3=Campeche25.8
3=Quintana Roo25.8
5Colima25.3
6Guerrero24.9
7=Chiapas24.1
7=Nayarit24.1
9Sinaloa24.0
10Veracruz23.7
Map of the warmest states in Mexico

The warmest states in Mexico. Click to enlarge. All rights reserved.

In both Canada and the USA, average temperatures tend to depend largely on latitude, ie. they increase towards the south of the country. This is clearly only partially the case in Mexico.

(a) What factors apart from latitude influence the average temperatures in Mexico’s states? Try to find evidence that either supports (or refutes) your ideas.

(b) Is there any connection between average temperature and precipitation amounts? Compare this map of states which are relatively warm with the states which have

(c) If you do not already know, can you guess where the coolest states in Mexico will be? Check here to find out if you are right!

Mexico’s diverse climates are the subject of chapter 4 of Geo-Mexico: the geography and dynamics of modern Mexico. Climate-related hazards are analyzed in chapters 6 and 7. Buy your copy today!

The 10 coolest states in Mexico

 Maps, Teaching ideas  Comments Off on The 10 coolest states in Mexico
Jul 262010
 

The table shows the ten coolest states in Mexico, defined by their average annual temperature.

RankStateAverage annual temperature (degrees C)
1Tlaxcala14.1
2=Estado de México15.2
2=Federal District15.2
4Chihuahua16.6
5=Zacatecas17.2
5=Aguascalientes17.2
7Hidalgo17.4
8Durango17.7
9Guanajuato17.9
10Baja California18.5
Map of the coolest states in Mexico

The coolest states in Mexico. Click to enlarge. All rights reserved.

In both Canada and the USA, average temperatures tend to depend largely on latitude, ie. they decrease towards the north of the country. This is clearly not the case in Mexico.

(a) What factors apart from latitude influence the average temperatures in Mexico’s states? Try to find evidence that either supports (or refutes) your ideas.

(b) Is there any connection between average temperature and precipitation amounts? Compare this map of states which are relatively cool with the states which have

(c) Can you guess where the warmest states in Mexico will be? To find out if you are right, you can find an atlas or on-line map showing average temperatures in Mexico, or keep reading the Geo-Mexico blog each day until we include our own map showing the warmest states!

Mexico’s diverse climates are the subject of chapter 4 of Geo-Mexico: the geography and dynamics of modern Mexico. Climate-related hazards are analyzed in chapters 6 and 7. Buy your copy today!

In which months are hurricanes most likely to strike Mexico?

 Other  Comments Off on In which months are hurricanes most likely to strike Mexico?
Jul 142010
 

The following verse provides a way to remember how likely hurricanes are in different months of the year. It applies specifically to Atlantic (Gulf of Mexico) and Caribbean hurricanes.

June, too soon
July, stand by
August, come it must
September, remember
October, all over.

This verse matches the historical records of Atlantic and Caribbean hurricanes fairly closely. Even so, to keep everyone on their toes, hurricanes sometimes, very occasionally, develop in other months of the year.

Previous hurricane-related posts:

Hurricane Alex, 30 June – 1 July 2010

Hurricanes and other climatological phenomena are analyzed in chapters 4 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico. Buy your copy today, so you have a handy reference guide available whenever you need it.

Mexican scientists and institutions involved in the IPCC (Intergovernmental Panel on Climate Change)

 Other  1 Response »
Jul 092010
 

The 4th Assessment Report (2007) of the IPCC (Intergovernmental Panel on Climate Change) involved the contributions of 2,500 scientists from 130 countries. The number of Mexican scientists participating was higher than the number from many richer countries including Spain and France. Sixteen Mexican scientists were involved in writing the 4th IPCC report. Ten of the sixteen hold positions at UNAM (the National University in Mexico City), making UNAM one of the institutions in the world with the highest rate of participation.

The 16 Mexican contributors were:
IPCC 4th Report

A further 8 Mexican scientists helped edit the documents:

Many of the same scientists have now been confirmed as members of the international team developing the 5th Assessment Report of the IPCC. In addition, the following newcomers have also been appointed:

  • Salvador Lluch-Cota, Centro de Investigaciones Biológicas del Noroeste, S.C. (Lead author, Ocean systems)
  • Fernando Aragon, El Colegio de la Frontera Sur (Urban areas)
  • Ursula Oswald-Spring, Centro Regional de Investigaciones Multidiscipinarias, UNAM    (Human security)
  • Roberto A. Sanchez Rodriguez, University of California, Riverside  (Adaptation planning and implementation)
  • Edgar Ortiz (Integrated Risk and Uncertainty Assessment of Climate Change Response Policies)
  • Martha Micheline Cariño Olvera (Social, Economic and Ethical Concepts and Methods)
  • Mauricio de María Campos (Sustainable development and equity)
  • Angel de la Vega     (Energy systems)
  • Xochitl Cruz-Nuñez (Transport)
  • Omar Masera (Agriculture, Forestry and other land uses)
  • Gian Carlo Delgado (Human Settlements, Infrastructure and Spatial Planning)
  • Alba Eritrea Gámez Vázquez (Regional Development and Cooperation)
  • Manuel Angeles (National and Sub-National Policies and Institutions)
  • Tomás Hernández-Tejeda, National Institute of Research in Forestry, Agriculture and Livestock (INIFAP)/SAGARPA (Synthesis Report)

Mexico’s diverse climates are the subject of chapter 4 of Geo-Mexico: the geography and dynamics of modern Mexico. Water availability, rivers, aquifers, water issues and hazards are analyzed in chapters 6 and 7. Buy your copy today!

How many hurricanes are likely in the 2010 Atlantic hurricane season?

 Mexico's geography in the Press, Updates to Geo-Mexico  Comments Off on How many hurricanes are likely in the 2010 Atlantic hurricane season?
Jul 012010
 

Philip Klotzbach and William Gray, of Colorado State University, have analyzed the atmospheric and oceanic conditions in the Atlantic immediately prior to the 2010 hurricane season. They conclude that this season’s hurricane activity in the Atlantic is likely to be stronger than has been the norm during the past 50 years. They predict that the Atlantic season will see 18 named storms, of which 8 will be classed as tropical storms, 5 as moderate hurricanes (1 or 2 on the Saffir-Simpson scale), and 5 as severe hurricanes (3, 4 or 5 on the Saffir-Simpson scale).

The popular press regularly warns us that on-going global warming will increase the frequency of hurricanes, and their intensity, allegedly due to warmer sea-surface temperatures in the mid-ocean hurricane-spawning areas. Klotzbach and Gray do not believe this. They studied the paths of all severe hurricanes (category 3, 4 or 5) for the fifty years from 1945-1994, dividing this time frame into two 25-year periods (see image).

Tracks of severe Atlantic hurricanes, 1945-1994

Tracks of severe Atlantic hurricanes, 1945-1994. Source: Klotzbach and Gray, 2010. Link to original article at end of this post. Click image to enlarge.

From 1945-1969 was a period of weak global cooling. There were 80 severe hurricanes in this period, some of them taking very erratic paths, with correspondingly dramatic impacts when they struck areas wholly unprepared.

Between 1970 and 1994, the Earth’s temperatures underwent a modest rise (global warming). However, in stark contrast to popular belief, far fewer severe hurricanes occurred during this period (38 in total), and they tended to follow entirely predictable paths.

Clearly the science behind hurricane formation is more complicated than some journalists would have us believe!

Klotzbach and Gray demonstrate the importance of the Thermohaline Circulation (THC) in the Atlantic. The THC is a large-scale circulation in the Atlantic Ocean that is driven by fluctuations in salinity and temperature. The 1945-1969 period coincided with a strong THC, whereas the 1970-1994 period was a time when the THC was weak.

What has happened since 1994? In the fifteen years from 1995-2009 inclusive, the THC was strong, and there were 56 severe Atlantic hurricanes. By comparison, in the preceding fifteen years from 1980-1994, when the THC was weak, only 22 severe hurricanes formed. So it appears that hurricane frequency is not linked to global warming or carbon dioxide (CO2) levels in the atmosphere, but to cyclical changes in the THC.

How accurate are the predictions for the 2010 hurricane season? Only time will tell…

Click here for Klotzbach and Gray’s original article (pdf).

Hurricane warnings in Mexico are the responsibility of the National Meteorological Service (NMS). The NMS also provides an archive of information about past hurricanes.

Hurricanes and other climatological phenomena are analyzed in chapters 4 and 7 of Geo-Mexico: the geography and dynamics of modern Mexico. Buy your copy today, so you have a handy reference guide available whenever you need it.

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