Maintaining the drains and sewers of Mexico City

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Jan 312012

How is Mexico City’s choking sewer system cleaned? Have you ever wondered who is responsible for the gross job of cleaning the city’s sewer system to help ensure it never gets blocked? Well, we did and were surprised at the answer…

To find out, click the link for this 4 minute video clip from our friends at National Geographic:

In previous posts, we looked at the history of attempts to drain Mexico City:

and at the construction of a massive tunnel to improve the city’s drainage:

At present, both the water supply system and the sewer systems of Mexico City are managed by a single government entity, the Sistema de Aguas de la Ciudad de México (SACM).

In 2008, the system’s main existing tunnel was shut down for its first maintenance in 35 years. To maintain the drains and sewers, Mexico City relies heavily on its experienced team of divers, all two of them! They are thought to be the only sewage divers in the world. This 2010 interview from the always interesting blog with diver Julio Cou Cámara is a mind-opening read.

In his own words, “What we mostly do is maintenance. We repair pumps, we take out debris—we take out bodies of animals, bodies of people, and all the rubbish. There’s so much rubbish in the drainage system, it’s very harmful to us and to the city. People are always wondering why there’s so much flooding in the city. I can tell you that the city floods because of all the rubbish that creates blockages in our drainage system. If we were maybe a bit more conscious about rubbish and we didn’t throw it on the street, we wouldn’t have this many flooding problems in the city.”

Frankly, this challenging job does not sound like much fun: “We work blindly in the black water. It contains animal poo, human poo, hospital waste… any kind of pollution you can think of. All of that is in the sewage water. That’s where we work.”

So, now you know! The sewers of Mexico City would function far worse if it wasn’t for the unsung heroism of workers like Carlos Barrios and Julio Cou Cámara.

(But if a vacancy comes up, please don’t call)

Nestlé helps program to regenerate Mexico’s coffee industry

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Jan 282012

Coffee trees are planted on 688,000 ha in 12 states, mainly in southern Mexico. The main coffee-producing states are Chiapas, Oaxaca, Puebla, Veracruz and Guerrero. As we reported in an earlier post, Mexico is financing a program to gradually replace aging coffee trees. The average yields of coffee in the 2010-11 season did show a slight increase on previous years. Officials hope this is the start of a trend of higher yields as the older trees are gradually replaced. The program to replace coffee trees is being supported by Nestlé, the Swiss food corporation.

Between 2002 and 2010, more than 4,000 growers in several states benefited from Nestlé’s distribution of more than 3.9 million coffee plants as part of a nationwide plan to replace aging coffee trees. Nestlé has since announced that it plans to establish its first coffee-propagation center in Mexico, in the southern state of Chiapas, in a joint venture with Agromod, a Mexican crop technology company, and the National Forestry, Farming and Fishing Institute (Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, INIFAP).

The project will supply 30 million coffee plants by 2020, and mean that Nestlé will no longer need to import coffee plants to Mexico from its facility in Tours, France. As many as 20,000 coffee-growers will benefit from the project. Most of the new plants will be arabica varieties (for premium beans); the remainder will be robusta varieties (used in instant coffee blends).

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Mapping remittance flows to Mexico, a practical exercise

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Jan 262012

Looking for a practical exercise about migration and remittance flows to challenge your students?

Remittances (the funds sent by migrant workers back to their families) are a major international financial flow into Mexico. Remittances bring more than 20 billion dollars a year into the economy, an amount equivalent to 2.5% of Mexico’s GDP. On a per person basis, Mexico receives more worker remittances than any other major country in the world. An estimated 20% of Mexican residents regularly receive some financial support from relatives working abroad. Such remittances are the mainstay of the economies of many Mexican families, especially in rural areas of Durango, Zacatecas, Guanajuato, Jalisco and Michoacán.

Two data tables [see link]  included in the World Bank Working Paper by Raúl Hernández-Coss, referred to in several previous posts, offer an ideal starting-point for practical mapping and analysis exercises for students. (The data is from 2004 but we are more interested in general patterns than precise values). The data tables are here:

A ready-made printable base map, showing the state boundaries of Mexico and USA, can be found here:

Suggested mapping exercises:

1. Which US areas have most Mexican migrants?

Use Column 2 (Mexican nationals living in this jurisdiction) of Table VI.A.1 and draw proportional circles on a base map to show which areas have most migrants. [To draw circles where the area of each circle is in direct proportion to the number of Mexican nationals, the first step is to calculate the square root of each number. These square roots are then used as the basis for working out the diameter (or radius) of the circle you draw for each location. The area of each circle is then proportional to the number of migrants. Remember to choose the most appropriate scale for the circles, so that it is easy to compare places. (If you draw very small circles, or super-large circles, they will be difficult to compare!)

2. Which US areas send the highest value of remittances back to Mexico?

Use column 4 of Table VI.A.1 to show the value of total “annual remittance flows” on a base map. You may be able to superimpose this information on the same base map you drew for Q1 which would make it very easy to see if the areas with most Mexican nationals send the most remittances back to Mexico each year. Can you see any anomalies on your map, either where an area sends far more remittances back than might be expected from the number of migrants, or where an area sends only a small value of remittances back despite having a very large number of Mexican nationals?

3. How does the “average remittance” (column 5 of Table VI.A.1 vary?

Use the available figures to see if you can identify any pattern to which areas send relatively large remittance payments, and which send much smaller average payments.

4. Where do all the remittance payments go?

Level One: Use the information from Table VI.A.2 to draw a map with arrows showing the largest single flows from each area in the USA to their corresponding state in Mexico.

Level Two: Work out the dollar value of the main remittance flows, by using the % figures given for some areas in Table VI.A.2 and their corresponding total annual remittance values from Table VI.A.1. (eg the value of the Los Angeles to Jalisco flow is 26% of $7,886.3 million). Then map the ten largest flows using flowlines (arrows where the width of each arrow is proportional to the value of remittances).

Look at the map or maps created and see if you can identify any patterns. If you can describe a pattern, then also look to see if you can find any anomalies, and try to explain your findings.

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Jan 232012

As we saw in an earlier post – Attempts to provide drainage for Mexico City date back to Aztec times – Mexico City has serious drainage problems. Because of the shifting subsoil as the land on which the city was built sinks an average of 10 cm/yr, the main drainage tunnels built years ago no longer have the slope (grade) they need to work efficiently. At least one of the feeder tunnels now slopes in the wrong direction!

This has greatly increased the risk of catastrophic flooding occurring. After years of discussion, authorities decided a few years ago that the only viable solution was to construct another major drainage tunnel to take pressure off the existing system and increase the maximum drainage rates following heavy storms.

The new tunnel, known as the Eastern Drainage Tunnel (Túnel Emisor Oriente), is said to be the world’s largest ever drainage tunnel and should be completed within the next couple of years. It is 7 m (23 ft) in internal diameter (wide enough for a tractor trailer) and can carry up to 150 cubic meters of water a second.

Map of tunnel route

Map of tunnel route; the new tunnel is in red, the existing Central Tunnel is in blue

The tunnel is 62 km (39 mi) long. It starts from the interceptor channel of Río de los Remedios and ends in a treatment plant in Atotonilco de Tula (Hidalgo), close to where the existing Central Drainage Tunnel flows into the El Salto River. Atotonilco receives 725 million cubic meters of water each year carrying 180,000 tons of garbage. Some of the treated water will be piped to the Mezquital Valley Irrigation District in Hidalgo where water usage exceeds natural replenishment rates. The remainder of the treated water will be given additional (tertiary) treatment before being piped into the overexploited underground aquifers to replenish them.

photo of new tunnelThe Eastern Drainage Tunnel construction project is one of Mexico’s largest engineering undertakings ever. The total investment (45% government, 55% private) is almost a billion dollars. Six massive boring machines are working in coordination, each boring a 10km section of the tunnel. The work is challenging, partly because of the varied nature of the rocks (limestone, volcanic rock, sand and clay) and partly because parts of the tunnel are as much as 200m (equivalent to 40 stories) below the surface.

Ventilation shaft of new tunnel

Ventilation shaft of new tunnel

The geography of wildfires in Mexico: the disastrous wildfire season of 2011

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Jan 212012

In the past 20 years, wildfires have destroyed 47,000 square kilometers (18,000 sq. mi) in Mexico, equivalent to five times the area of all sections of Mexico City’s Chapultepec Park, the largest urban park in Latin America. The average fire in Mexico affects 32 hectares (80 acres); this figure has not changed significantly in recent years, even though the incidence of fires has increased somewhat due to a combination of climate change and an increase in the number of people living on the margins of forested areas. The National Forestry Commission (Conafor) says that 99% of Mexico’s forest fires are caused by human error, and only 1% are due to natural causes such as lightning strikes.

It generally takes about 30 years to rehabilitate forest areas ravaged by fire, with reforestation costing up to $2400/ha.

Wildfires are not entirely bad. For example, they help regenerate grassland areas, especially, with fresh young plants. On the other hand, in addition to protecting the existing vegetation, stopping wildfires when they occur helps to preserve soil structure and prevents additional emissions of CO2 from the burning of more plant material. At a national level, it is estimated that fires result in the erosion of 86 million metric tons of soil a year.

In a 2009 study, Conafor used 17 variables to identify the areas of the county with the highest risk of wildfires. Three broad areas accounted for the 900,000 square kilometers identified as having either a “medium” or “high risk” for wildfires:

  • i. Yucatán Peninsula, Chiapas, Oaxaca and Guerrero
  • ii. Central Mexico – Veracruz, Tlaxcala, Puebla, México, Michoacán, Jalisco and the Federal District. This area has more fires than any other because local populations often use fire to clear fields before planting.
  • iii. Baja California. This is the only area where the main fire season is in summer, from March to November. This is the rainy season in the remainder of Mexico, where the fire season corresponds with the winter dry season.

The first half of 2011 was an especially bad period for wildfires in Mexico, the worst for at least 30 years.

Coahuila wildfire, April 9, 2011 (Earth Observatory, Landsat-5)

Coahuila wildfire, April 9, 2011 (Earth Observatory, Landsat-5)

During the first half of 2011, serious wildfires devastated several areas of northern Mexico, with the states of Coahuila and Nuevo León being hardest hit. Other states badly affected included Durango, Chihuahua, Quintana Roo, Oaxaca, Puebla and Guerrero. More than 7,800 fires occurred, severely damaging a total area of 4100 square kilometers. 30 of Mexico’s 32 states were affected; only Tabasco and Baja California Sur escaped unscathed.

Conafor’s annual fire-fighting budget for the entire country is only 650 million pesos ($50 million dollars); the average annual area damaged by wildfires is only 2600 square kilometers, of which 500 square kilometers are forest. At the height of the 2011 fire season, more than 60 new fires were being reported each day, according to Conafor.


In the state of Coahuila, fires damaged 250 square kilometers in four weeks. It is believed that 50% of these fires were due to farmers losing control of deliberate burns. Farmers are supposed to have an adequate fire-suppression plan in place before setting a deliberate burn, but in practice this requirement is not enforced.

The main locations were La Sabina and El Bonito. Authorities were very slow to respond. Diana Doan-Crider, a wildlife biologist at Texas A&M University, has spent the past 25 years studying the Mexican black bear in the Serranía del Burro in Coahuila, an ecological corridor that runs parallel to the Eastern Sierra Madre. The area includes a large population of Mexican black bears. Doan-Crider claims that authorities completely ignored the first warnings and that their eventual response (two weeks after the first fires started) lacked adequate coordination. Many mother bears and their young cubs perished in the fires.

Firefighters in Coahuila had to cope with a spectacular but terrifying fire whorl or fire tornado

Nuevo León

In the neighboring state of Nuevo León, large swathes of ranching land were ravaged by fire. One rancher who lost more than 10,000 ha of cattleland was equally critical of the slow response time of firefighters who took more than two weeks to appear on the scene, by which time the fires had taken hold.

David Garza Lagüera had converted his 14,000 ha ranch into the Cumbres de Monterrey National Park, one of the key areas of bear habitat. The largest pines on his land were more than 150 years old. All were totally destroyed.

The worst damage was in Galeana, Montemorelos, Zaragoza, Aramberri and Mina. The area burned in Nuevo León in May 2011 was almost ten times the total area affected in the state for the whole of 2010.

Why was the 2011 fire season so bad?

To quote the Earth Observatory, “Lack of winter rain and frost left the plants dry and prone to fire. On top of that, the area has not burned for more than 20 years, during which time fuel built up. Thunderstorms and steady strong winds with gusts up to 110 km/h (70 mph) completed the formula for a dangerous, fast-moving wildfire.”

Ironically, the passage of Hurricane Alex in July 2010, which brought 1500 mm (60″) of rain to the Serranía del Burro, actually worsened the fire damage the following year. The rain from Hurricane Alex encouraged so much new growth in the final months of the rainy season that when it died back in the dry season, there was far more fuel available than usual for any wildfire that was sparked.

By the time the federal government declared a state of emergency, it was too late; the fires had already destroyed large areas of grassland, scrubland and forest. The emergency response when it finally arrived included help from the USA and Canada such as the specialist aerial Mars water-bombers stationed on Vancouver Island. The fires were only fully extinguished once the annual rainy season arrived.

As we now know, the disastrous fires of April-May 2011 were an early sign of Mexico’s worst drought for 70 years:

How sustainable is organic agriculture on the Baja California Peninsula in Mexico?

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Jan 192012

In recent years, a farming boom has completely changed the landscape in parts of Mexico’s Baja California Peninsula. The new landscape is comprised of organic farms, specializing in growing fresh produce, especially out-of-season, certified organic, fruits and vegetables, which carry premium prices.

“Organic” has come to mean very different things in different countries, but the essential common element is that it uses no synthetic fertilizers, hormones or pesticides. In the USA, the term “organic produce” also requires that farmers protect water resources, though this is hard to define and at least as hard to enforce.

The Baja California Peninsula receives very little rainfall, so irrigation water for its organic farms comes from underground aquifers. The profitability of these new farms relies on the availability of irrigation water and on the proximity of the region to the lucrative US market for organic produce.

The new farms may be “organic”, but the bigger question, examined by Elisabeth Rosenthal in Organic Agriculture May Be Outgrowing Its Ideals, in the New York Times is, “Are these organic farms sustainable?” Rosenthal looks in some detail at whether or not organic farms protect the local environment and the livelihood of local farmers. The article discusses the extreme stress being placed on the area’s ground water reserves. Some farmers are already in trouble because their wells have dried up. More than one-third of aquifers in the southern part of the peninsula are officially classified as “over-exploited”.

Growers blame the area’s tourism industry for the water shortages, arguing that hotels and golf courses gobble up far more than their fair share of the precious resource. Despite the aridity of the southern section of Baja California Peninsula, the southern coast, centered on Los Cabos, has far more golf courses per unit area than anywhere else in the country.

The “organic” label also takes no account of the emissions involved in production and transport of fruits and vegetables to the marketplace; export-oriented horticulture in the Baja Peninsula is an energy-intensive enterprise. Adding to the unsustainable side of the argument, some of the organic farms practice “monoculture”, growing a single crop year after year on the same land, a system known to lead to soil depletion and increase the risk of pest-related problems.

On the other hand, the new farms also provide an alternative source of jobs to tourism. Del Cabo, which has a cooperative packing plant in San José del Cabo and trucks or flies more than 7 metric tons of produce to the USA every day, is able to help its members by supplying high-quality seed, and employing specialists in plant raising and plant diseases who act as consultants to individual farmers as required. Del Cabo criticized the New York Times story for its numerous inaccuracies regarding water usage and sustainability.

Conscious of the water issues, many of these modern organic farms employ sophisticated, water-conserving irrigation systems, such as computerized drip irrigation. They also grow many crops under shade. Such systems are expensive to install and maintain, so most of the bigger producers are US-owned companies.

In Organic Tomatoes in January: Sucking Mexico Dry, in Mother Jones, Tom Philpott compares the situation in Baja California with that in “another region famous for winter tomatoes and dirt-cheap labor costs: Immokalee, Florida, source of a huge percentage of non-organic winter tomatoes consumed in the United States.” Philpott concludes that “What’s going on in Baja seems more about generating a premium-priced product while systematically degrading a landscape. Want organic tomatoes in the cold months? Buy them in a can.”

Food for thought!

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Lack of global interactions…

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Jan 192012

Owing to circumstances beyond our control, was offline for much of yesterday (Wednesday), along with hundreds of other servers in a central Vancouver server farm.  We apologize for any inconvenience caused.
I’m not sure of all the details, but it appears that a construction crew working on a nearby street severed an important cable…

The good news is that we’re back now, and have lots of interesting things to share with you in the coming weeks,


The urgent need for reforestation of hills near Mexico City

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Jan 172012

A coniferous tree plantation is being formed on the lower slopes of Ajusco, the 3,930 m (12,894 ft) volcanic peak that overlooks the southern part of Mexico City. After decades of uncontrolled land clearance, local farmers are replanting 800,000 trees as part of a sustainable project which will ensure them a reliable income for years to come. Mexico’s National Forest Commission estimates that mature coniferous plantations are highly profitable, and should repay farmers a 500% return on their investment. Individual trees have to be at least 8 years old before they can be harvested.

Three species of conifers are being planted: the Sacred Fir (oyamel), Douglas Fir and Mexican White Pine (ayacahuite). At present, only about one-third of Christmas trees sold in Mexico are natural trees, with 60% of these having to be imported from as far away as Canada.

The project will not only increase farmers’ incomes, it will also reduce soil erosion, increase carbon storage, and bring hydrological benefits. Mexico City has seriously depleted its aquifers – see Why are some parts of Mexico City sinking into the old lakebed? Reforesting the hills surrounding the city means more water will be retained in the soil, and less will runoff into the city’s already-stressed network of storm drains.

Ajusco is not the only volcanic peak near Mexico City where deforestation has become a major issue. In August 2011, National Water Commission (Conagua) officials blamed serious flooding in the Rayón municipality of the State of México on the uncontrolled logging of the lower slopes of the Nevada de Toluca volcano.

The lack of protective forest cover meant that heavy rain caused the River Santiaguito to burst its banks and flood homes in the community of San Juan La Isla. The situation would have been far worse if Conagua had not ordered the dredging of 12,000 cubic meters along a 4 km stretch of the river bed in 2009. Following the 2011 floods, Conagua reiterated the need for more reforestation and called for stricter land use controls to prevent similar problems in the future.


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).

Want to read more?

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Four new municipalities change the map of Chiapas

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Jan 142012

The Chiapas state government has redrawn the map of its municipal boundaries to create four new municipalities (municipios), bringing the number in the state to 122. The four new municipalities are:

1. Belisario Domínguez (formerly part of the municipality of Cintalapa de Figueroa). The new municipio aims to resolve a long-standing agrarian conflict over land and forest rights with San Miguel Chimalapa and Santa María Chimalapa, both in neighboring Oaxaca. The municipal seat of the new municipality is Rodulfo Figueroa. The municipality also includes the settlements of Gustavo Díaz Ordaz, La Hondonada, San Marcos, Montebello and Flor de Chiapas.

2. Emiliano Zapata is the new municipality responsible for the 20 de Noviembre ejido, formerly part of the Villa de Acala municipality.

3. El Parral, previously the largest settlement in Chiapas that was not a municipal seat, now becomes the municipal seat for the El Parral ejido, formerly part of the Villacorzo municipality.

4. Mezcalapa is a new municipality which serves the settlement of Raudales Malpaso, cut off decades ago from its former municipal seat of Tecpatán by the construction of a reservoir.

The total number of municipalities (municipios) in Mexico is currently 2,458. Note that this figure includes the 16 delegaciones (boroughs) of Mexico City which, while technically not municipalities, do have significant autonomy.