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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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.

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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

2013 Hurricane Names for the Eastern Pacific

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.


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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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

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.