The pattern of violent crimes in Mexico in 2013

 Mexico's geography in the Press, Updates to Geo-Mexico  Comments Off on The pattern of violent crimes in Mexico in 2013
Feb 082014

The Consejo Ciudadano para la Seguridad Pública y la Justicia Penal AC, a Mexican non-profit, has published an interesting report looking at the levels of violent crime in Mexico in 2013:

The authors take violent crimes to include intentional homicide, kidnapping, rape, aggravated assault, robbery with violence and extortion.

At the municipal level, violent crime is concentrated in a relatively small number of municipalities. The report looks at the statistics for the 216 municipalities (including delegaciones of the Federal District) that had estimated populations of over 100,000 in 2013. Since 2012, four municipalities have joined this group: El Fuerte (Sinaloa), Tepotzotlán (México), Pánuco (Veracruz) y Playas de Rosarito (Baja California). Between them, the 216 municipalities are home to about 64% of Mexico’s total population.

Data from government agencies and INEGI were used to compile rates for each crime in each municipality. These rates were then multiplied by the following weightings (to reflect the relative severity and impacts of each type of crime),

  • 0.55 for intentional homicide
  • 0.22 for kidnapping
  • 0.13 for rape
  • 0.04 for aggravated assault
  • 0.03 for robbery with violence
  • 0.03 for extortion

and summed to give an overall index for “violent crimes”.  For the 231 municipalities, the index ranged from 106.63 for Oaxaca, Oaxaca to 0.00 for Zapotlán el Grande in Jalisco. The full details of the methodology are explained and discussed in the report. A similar methodology was also used to calculate levels of violence by state.

The worst 10 municipalities in terms of violent crime were:

  1. Oaxaca, Oaxaca – violent crime index value of 106.63
  2. Acapulco, Guerrero – 80.35
  3. Cuernavaca, Morelos – 65.30
  4. Yautepec, Morelos – 56.19
  5. San Pedro, Coahuila – 53.42
  6. Cd. Victoria, Tamaulipas – 52.48
  7. Iguala de la Independencia, Guerrero – 52.25
  8. El Fuerte, Sinaloa – 50.82
  9. Jiutepec, Morelos – 50.29
  10. Torreón, Coahuila – 49.31

The national index (ie treating the entire country as a single entity) was 23.17, meaning that the index value for violent crimes in Oaxaca, Oaxaca, was more than four times that of the country as a whole.

Municipalities which were in the worst twenty in 2012 for violent crime, but have now fallen out of that group include: Lerdo (Durango) Zacatecas (Zacatecas), Cuautla (Morelos), Zihuatanejo (Guerrero), Temixco (Morelos), Cuauhtémoc (DF), Tecomán (Colima), Navolato (Sinaloa), Centro (Tabasco) and Monterrey (Nuevo León).

Moving into the worst twenty for the first time are: Playas de Rosarito (Baja California), Hidalgo del Parral (Chihuahua) San Pedro (Coahuila), Chilpancingo (Guerrero), El Fuerte (Sinaloa) and Chalco, Cuautitlán, Cuautitlán Izcalli, Ecatepec and Naucalpan (all in the State of Mexico).

Of the 213 municipalities, Acapulco had the highest intentional homicide rate (112.81/100,000, about 6 times the national rate of 19.05/100,000). Cd Victoria had the highest kidnapping rate (23.28/100,000, 15 times higher than the national rate of 1.46/100,000, though kidnapping rates in Mexico are notoriously unreliable, and have been the subject of intense press debate in recent months).

Violent crimes by state, 2013

By state (see map), Guerrero had the highest violent crime index with 47.76 points, followed by Morelos 43.99 and Chihuahua 40.87. In general, with the prominent exceptions of the State of México and Guerrero, the southern half of Mexico appears to be somewhat safer than the northern half.

Map of Violent crime index, 2013

Violent crime index, 2013. Source of data: see post. Credit: Geo-Mexico

For individual categories of crime at the state scale, Morelos had the highest kidnapping rate (8.24/100,000). Quintana Roo had the highest rate of rape (28.31/100,000, compared to national average of 11.36/100,000). The State of Mexico had the highest rate for aggravated assault (251.64/100,000 compared to national average of 130.21/100,000). Morelos came out on top for the highest rate of robbery with violence (455.08/100,000 compared to national average of 182.61) and for the highest rate of extortion (21.96/100,000 compared to national average of 6.94/100,000).

Good news for tourists

According to this report, almost all of Mexico’s major tourist destinations (with the noteworthy exception of Acapulco) are located in areas where violent crime is below the national average.

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Jan 022014

The total number of people living in poverty in Mexico continues to rise, though the poverty rate (as a percentage) remains roughly the same. According to Mexico’s National Political and Social Development Commission (Spanish language acronym: Coneval), the number of people in poverty has risen steadily for several years, much in line with Mexico’s rising total population. Coneval’s figures are based on a simple multidimensional poverty index, which considers the following criteria:

  • household income
  • access to education
  • access to food
  • access to health care
  • access to social services
  • housing quality
  • access to basic household services (electricity, water, drainage)

According to Coneval, 53.3 million Mexicans (45.5% of the total population) were living in poverty in 2012, compared to 52.8 million (46.1% of the then population) in 2010 and 48.8 million Mexicans (44.5%of the population) in 2008.

Note that poverty statistics prior to 2008 in Mexico were generally based purely on income levels. From 2008, this method was replaced by a multidimensional index. The precise details of the index have been modified slightly since that time, making exact comparisons between 2012 and 2008 more problematic.

While the precise numbers are subject to debate, mainly due to differing definitions of what constitutes “poverty” and how it can be measured, the trend revealed by the Coneval numbers is supported by the Economic Commission for Latin America and the Caribbean (ECLAC) in its “Social Panorama of Latin America 2013“, published in December 2013. The ECLAC report found that Mexico is one of a very few countries where poverty levels rose between 2011 and 2012, from 36.3% of the population to 37.1%, according to its definition.

The dire situation in Mexico compares to a slight decrease in poverty in most larger Latin American countries, including Venezuela, Ecuador, Brazil, Peru, Argentina and Colombia.

In absolute terms, according to ECLAC, 164 million people were found to be living in poverty in Latin America, about 57.4 million (35%) of them in Mexico.

Change in poverty rates in Mexico, 2010-2012.

Change in poverty rates in Mexico, 2010-2012. Credit: Geo-Mexico; all rights reserved. Data: Coneval

The map shows the Coneval data for changes in the poverty rate between 2010 and 2012 by state. It appears that poverty levels increased in many of Mexico’s more prosperous areas and in the longer established industrial areas, as well as in almost all areas where tourism is important. Poverty decreased in some of Mexico’s more rural, and generally poorer, states.

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Example of a sixteenth century map

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Dec 072013

In the mid-sixteenth century, the Spanish Court was determined to acquire accurate information about everything being encountered in New Spain. This led to a series of censuses and accounts, including the Relaciones geográficas (Geographic Accounts).

The basis for the Geographic Accounts was a 50-question survey, sent to New Spain in 1577. The authorities in each administrative center were instructed to call a meeting of the “Spaniards and other natives in the district”, to find out everything they could about the area’s geography, people and history.

Of the 191 known responses to the 1577 questionnaire, 167 have survived in archives to the present day. Most of the original responses are housed in Spain, in either the Archivo General de las Indias in Seville or the Real Academia de la Historia in Madrid, while a further 43 responses form part of the Benson Latin American Collection in the University of Texas library in Austin. (The library’s webpage about the Relaciones geográficas has several links to images of sample pages and maps).

Map of Zempoala area from the Relaciones Geográficas

Map of Zempoala area from the Relaciones Geográficas (1577)

The accounts contain a wealth of information about population, relief, flora, fauna, economic activities and lifestyles. Some also include maps of the areas being described. However these early maps do not follow modern conventions in terms of having a uniform scale across the area being shown, or an orientation that is consistent in terms of compass directions. They are pictorial maps, where the scale varies across the map, and where areas are delimited, or places are linked, without apparent regard for direction.

One such map (see image above) depicts the area around Zempoala (Hidalgo). This is analyzed by Barbara E. Mundy, Associate Professor of Art History at Fordham University, in an online article, Mapping Babel: A Sixteenth-Century Indigenous Map from Mexico, published in The Appendix, a “journal of narrative and experimental history”. In the article, Mundy provides a detailed, step-by-step account of the map, with lots of additional related images and information.

Detail of map, showing Tepemayalco

Detail of map, showing Tepemaxalco

Mundy’s analysis reveals several “acts of translation” that have been made by the indigenous artist(s) presumed to be responsible for drawing the map.

For example, the artist(s) made the Spanish paper provided for the map more closely resemble its indigenous counterpart (bark paper), by joining sheets together to create the size they wanted for the map. In addition, unlike modern maps where the viewer is essentially static, with the map details arranged around them, indigenous maps demand changes of perspective, mobile viewers, who have to reorientate themselves depending where they are on the map in order to see things clearly.

Many of the images are a translation, perhaps of similar European images. For instance, like most towns on the map, Tepemaxalco is shown with “a conventional sign for a Christian chapel: a small building drawn in perspective with one side marked by a shadowing grey wash, topped with belfry and cross.”

The map also links the pictograph for each place name to its name written in alphabetic script. “The pictograph for Tepemaxalco (see image) registers some of its Nahuatl components: tepetl, ‘hill,’ maitl, ‘hand,’ xalli, ‘sand’ and co, ‘place of.’ Below, the name is written in alphabetic script, probably introduced by the Franciscans who evangelized this region.”

The dominant pictogram on this map is that for Zempoala (written “Cenpoballa” on the map). Mundy offers an interesting interpretation of this pictograph, which we hope to examine further in a future post.

Further reading

Barbara E Mundy. 2001. The Mapping of New Spain: Indigenous Cartography and the Maps of the Relaciones Geográficas.

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Nov 162013

In an alliance with the Sonoran Institute, the National Geographic Center for Sustainable Destinations helped the region’s communities create the first transborder Geotourism MapGuide, covering northern Sonora and southern Arizona. The mapguide was published in 2007:

The maps  have vignettes of information about history, culture, geology and many other aspects of the region, making it a useful guide for geo-tourists. While some might argue about the choice of locations and attractions described on the maps, this is a useful addition to the background reading for anyone thinking of traveling to this region with some time on their hands to explore.

Surprisingly, the map has only a very brief and somewhat dismissive mention of the El Pinacate and Gran Desierto de  Altar Biosphere Reserve:

“Stand at the rim of this mile-wide volcanic crater and you may feel as if you’re on the moon. This land of ancient lava, sand, and cinder cones is sacred to the O’Odham people. Today, those on the Sonora side of the border call themselves “Pápago.”

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The growth of the city of Monterrey, Mexico’s industrial powerhouse

 Excerpts from Geo-Mexico, Other  Comments Off on The growth of the city of Monterrey, Mexico’s industrial powerhouse
Oct 282013

A series of historical maps of the city of Monterrey was published earlier this year in the city’s online Catalog of Buildings of Historic and Artistic Importance in Barro Antiguo, The maps, dated 1765, 1791, 1846, 1865, 1922, 1933 and 1947 respectively, offer a good basis for considering the urban growth of Monterrey, the industrial powerhouse of northern Mexico.

In chapter 22 of Geo-Mexico, the geography and dynamics of modern Mexico, we explained why, “Monterrey does not fit the general Latin American urban model as well as Mexico City or Guadalajara. First, it never really existed as a colonial city. Secondly, its development was more heavily dependent on industry. Thirdly, its relative wealth and progressive leadership in some ways make it more similar to a North American city than a Latin American city. It fits the model only in that it developed a definite high status sector in contrast to lower status industrial sectors, and eventually became spatially fragmented.”

But just how did Monterrey develop as a city? In each of the following historical maps of Monterrey, Barrio Antiguo (16 blocks in size in the present-day city) is marked by a red quarter-circle, which is an easy way to check each map’s orientation and scale. Monterrey was founded in 1596. The earliest map in our series, for 1765, shows that, even by that date, Monterrey was still a relatively small settlement situated between a (seasonally dry) “stream formed by various springs” (to the top of the map, north) and the seasonally-dry “Monterrey River” (now called the Santa Catarina River). The Barrio Antiguo is shown as mostly an empty area, with only one major construction.

Monterrey 1765

Monterrey 1765

Very little has changed by 1791 (see map below: note that this map is oriented south-upwards), though the Barrio Antiguo has now been developed, and is shows as having several streets in a clear grid pattern:


Monterrey in 1791

The grid pattern for Barrio Antiguo is equally evident in the details of the map in 1846:


Monterrey in 1846

As of 1846, no development is shown on the south bank of the Santa Catarina River, though tracks are shown heading east and south-east respectively from the city. The next map, for 1865, shows that the city is beginning to expand to the south. A substantial settlement is developing on the south bank, more of less opposite the Barrio Antiguo. Note, though, that this map shows only part of the city:


Monterrey in 1865

Clearly, Monterrey only emerged as a real city after the colonial period which ended in 1821. The relatively small city did not experience real growth until late in the 19th century when it became connected by railroad and started to attract industrial development.

Early in the 20th century, investors built the then largest iron and steel works in Latin America a few kilometers east of the city center. Many related industries located nearby. These industries and the railroad, which ran east–west about four kilometers (2.5 mi) north of the city center, stimulated early industrial development in these directions. Developers established low income housing tracts for industrial and other workers on the east, north and west periphery of the city. Neighborhoods for the wealthier classes were developed south of the city center.

By 1933, Monterrey has grown significantly in area, especially towards the north:


The city of Monterrey in 1933

Between 1933 and 1947, the city continues to expand, with many areas being infilled with residences:


The city of Monterrey in 1947

The city experienced another surge of industrialization and immigration in the 1950s and 1960s. Industrial development continued after 1970 when the national government implemented policies to shift development away from Mexico City. Monterrey became a major producer of steel, metal fabrication, cement, beverages, petrochemicals, food, telecommunications, auto parts, glass, and house furnishings. It also developed into a major financial center and one of the wealthiest and most progressive cities in the country.

Low income housing became a serious problem after the 1960s as the inner city tenements became extremely crowded. The government was not sympathetic to irregular housing schemes, so low income groups established numerous illegal squatter settlements on vacant land near the industrial zone. Government made a few efforts to remove these, but most survived and eventually became regularized.

The high status sector expanded south-west into San Pedro Garza García, which became one of the wealthiest municipalities in Mexico. The high overall income and wages in the city meant that many workers could afford home ownership and private automobiles. As a result, many gated communities (large and small) and suburban shopping malls were built around the urban periphery. The urban area became relatively fragmented with many low income residential zones located near high income areas.

Source of the maps used in this post:

Other posts about the urban geography of Mexico’s cities:

The pattern of homicides in Mexico in 2012

 Mexico's geography in the Press  Comments Off on The pattern of homicides in Mexico in 2012
Aug 172013

Homicide rates in Mexico increased between 2010 and 2012, though there is some evidence that they are now beginning to fall again. Did the pattern of homicide rates also change since 2010?

The top map shows the pattern of intentional homicides in Mexico in 2010. As we commented at the time, this map shows “that many northern states like Chihuahua, Sinaloa, Nuevo León and Durango are plagued by drug war violence and have very high murder rates. On the other hand, most states in the south and southeast, like Yucatán, Campeche and Tlaxcala are relatively free of drug war violence and historically have had low murder rates. One significant anomaly in the overall pattern appears to be Guerrero which is well to the south but has a high murder rate and a very significant amount of drug violence.”

Map of intentional homicide rate, 2010

Map of intentional homicide (murder) rate, 2010 Credit: Tony Burton / Geo-Mexico

The second map shows the pattern of intentional homicides in Mexico in 2012. (Note that the values on the key are slightly different to reflect the increase in Mexico’s average (nationwide) homicide rate between 2010 and 2012).

Map of homicide rates in Mexico, 2012, Credit: Tony Burton/ Geo-Mexico

Map of intentional homicide (murder) rates in Mexico. Credit: Tony Burton/ Geo-Mexico

At first sight the pattern in 2012 look pretty similar to that for 2010. The adjoining states of Sinaloa, Chihuahua and Durango continue to have rates well above the national average, as does Guerrero further south. However, the homicide rate in Nuevo León, which was “well above average” in 2010 has declined somewhat to “above average” in 2012. Since 2010, the north-eastern state of Tamaulipas has seen its homicide rate increase from “above average” to “well above average”. Perhaps more significantly, the border state of Coahuila has witnessed a jump from “below average” to “well above average”. Homicide rates in the two north-west border states of Baja California and Sonora have fallen since 2010 to “below average”.

Elsewhere, homicide rates have increased in both Zacatecas and in Colima since 2010, while rates in Veracruz have declined to “below average”. The shift in Veracruz means that a broad swathe of southern Mexico, including the Yucatán Peninsula, Oaxaca and Chiapas, now has a homicide rate “below average” or “well below average”, good news for tourists headed for Oaxaca, Cancún and the Riviera Maya!

On a more cautionary note, the state of Michoacán has seen increased violence in 2013; its homicide rate is headed upwards.

The changes in pattern of homicides between 2010 and 2012 are partially attributable to the “zones of contention” between rival drug gangs. For instance, the Knights Templar cartel (currently thought to be Mexico’s third largest cartel, behind the Zetas and the Sinaloa cartel) has its origin in  Michoacán but has expanded its geographic influence very rapidly in the past few years. Equally, the capture of key cartel leaders in recent years seems to herald increased violence as rivals compete to fill the perceived power vacuum left behind. This unfortunate outcome from the arrest of leading cartel operatives is continuing this year following the capture of Zeta leader Z-40.

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Mexico’s seven climate regions

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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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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

 Excerpts from Geo-Mexico  Comments Off on The three main causes of precipitation in Mexico
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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Map of Yucatán Peninsula including Campeche, Mérida, Cancún, Riviera Maya and Cozumel

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Mar 092013

Mexico’s Yucatán Peninsula, a low, flat limestone platform, is the most recently formed part of Mexico. The low topography, which is quite similar to western Cuba and southern Florida, is virtually all below 150 m (500 ft). The submerged western and northern portion of this platform is known as the Campeche Bank. The peninsula was connected to Cuba until the bridging section sank below sea level forming the Yucatán Channel. The west and north coasts are marked by lagoons, mangrove swamps and sand bars. The emergence and infilling of coastal lagoons in the southeastern and southwestern extremities of the peninsula have resulted in areas of marshland interspersed with remnants of the original lagoons.

Offshore to the east lie coral reefs. Most of the peninsula has shallow, highly permeable soils and virtually no surface water. However, underground water is relatively abundant. The peninsula is honeycombed with extensive underground cave systems, which are connected periodically to the surface via hundreds of natural sinkholes (cenotes). The ancient Maya believed that these cenotes led to the underworld.

Map of Yucatán Peninsula. Copyright 2010 Tony Burton. All rights reserved.

Mexico’s Yucatán Peninsula includes three states: Campeche, Yucatán and Quintana Roo. This region is the ancestral home of the Maya. There are about 800,000 Maya-speakers in Mexico, almost all of them living in this region. There are literally thousands of archaeological sites scattered across the peninsula, including many that are open to the public. Among the more famous are Uxmal, Chichen Itza, Calakmul (all three are UNESCO World Heritage sites), Tulum and  Coba. The city of Campeche (capital of the state of the same name) is also a World Heritage site on account of it being a walled city, one of the very few remaining in Mexico.

The state of Yucatán was important for sisal production. Between 1870 and 1920 the area experienced an economic boom based on the production of twine from sisal (oro verde or green gold). In order to transport the  sisal from the fields to processing centers and from there to the port of Sisal for export, plantation owners built an extensive (4500-km-long) network of narrow gauge railroads:

Quintana Roo is best known today for its tourism industry. The centrally planned resort of Cancún is Mexico’s leading tourist destination:

In Quintana Roo, 54% of the residents were born outside the state. These residents were mostly attracted to Quintana Roo by the rapidly growing tourist industry in Cancún and further south in the area known as the Maya Riviera. Almost 13% of Quintana Roo residents moved into the state within the last five years.

The Yucatán Peninsula has several important biosphere reserves:

  • Ría Celestún (Yucatán and Campeche): coastal region including important wetlands and drowned river valley (ría) with diverse fauna and flora, including flamingos.
  • Región de Calakmul (Yucatán): diverse tropical rainforests; the largest forest reserve in Mexico, with important Maya sites; ecotourism project.
  • Ría Lagartos (Yucatán): coastal estuary with diverse birdlife including more than 18000 pink flamingos as well as some 30,000 migratory birds.
  • Arrecife Alacranes (Yucatán): the largest coral reef in the Gulf of Mexico, and the only one in Yucatán state.
  • Sian Ka’an (Quintana Roo): coastal limestone plain, and extensive barrier reef system on Caribbean coast, with numerous archaeological sites; more than 4,000 plant species.
  • Banco Chinchorro (Quintana Roo): mosaic of open water, sea grass beds, mangroves, sandy beaches and coral reefs; more than 95 species of coral.

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