My article in last week’s Reporter described how the flow of the Lerma River to Lake Chapala had been reduced by 90 percent or more from 1930 to 2001. This was due primarily to a grossly excessive commitment to irrigation in the Lerma River basin, and the construction of over 500 dams and reservoirs that could store the river’s entire flow. Despite 40 years of discussions and hundreds of pages of studies and rules, no solution has been executed. The key factor is this: for each one percent saved of the 80 percent of the river’s flow that is now used for irrigation, it will be possible to provide domestic water for 400,000 persons.
The Guadalajara metro area, with 4.5 million people today, will grow to a population of nine to 12 million in the coming 50 years. For the required water to come from the Lerma River basin it will be necessary to reduce the irrigation use by 20 percent, that is learn how to irrigate with 60 percent of the river’s flow. To move in this direction both the farmers in the river basin and Guadalajara must change their ways.
At this time a 15-percent savings by the farmers may be achieved in just a few years by first replacing Babylonian era flood irrigation with modern, more efficient methods suited to both grain and row crops. Second, great reductions in irrigated land area and water use can be gained by switching to various higher valued crops. For example, tomatoes can produce the same income as corn but with a fourth the land area. Pecans can save even more. Hydroponic greenhouses offer 15 to 20 times as much food per hectare/year as field crops.Since irrigated water is very seldom metered, farmers have no incentive to invest in changes. Consider that only five percent of the income for 12 million people living in this river basin comes from current antiquated farming practices that consume 80 percent of the river’s water. If the cost of water is slowly increased from the current zero to one peso and then two and perhaps three pesos per cubic meter of water, farmers will reduce water use by conserving it better and electing to grow higher income producing crops on smaller irrigated areas. Only money put in or taken out of one’s pocket will lead to change.
Guadalajara has also two major changes to consider. First it must address the 20 to 30 percent loss of the water supply in over 7,000 kilometers of leaking pipes buried in the city’s streets. While the volume of the water wasted by the Lerma River basin farmers is 20 to 30 times greater than these water losses in Guadalajara, the news media have only focused on the latter.
It will take significant funding to replace or repair leaking pipes in the city. With many customers not paying their water bills and the inter-municipal water agency Siapa more than two billion pesos in debt, a miracle is needed. Such a miracle does exist!
Second, Guadalajara must dispel the myth that a major portion of any water sent to Lake Chapala is lost to evaporation. In truth, the rain that falls directly into the lake plus that coming in as local runoff offsets more than 90 percent of the volume of evaporated water. The challenge is that the basin proponents have assumed that the lake, as part of the Lerma River watershed, does not benefit from the rain in the lake’s own basin which never becomes part of the Lerma River flow.
As to the proposals for building mega dams east of the city, only the El Zapotillo Dam on the Verde River offers some promise. The most that can be expected from that direction is enough water for one million more people.
In regard to rainwater collection – which is great in rural areas and places with monthly rainfall – the cost to collect and store water inside a city each year for an eight-month dry spell is prohibitive. If to be done by families the cost would be about 700,000 pesos per household. If done by the city the cost would be more than 230 billion pesos, and the storage tank would have to be three meters high and 10 kilometers on a side! By contrast water storage at nature’s own Lake Chapala has been free for 10,000 years.
Once Guadalajara reaches 20 million people the only direction for more water will be desalinating it from the Pacific and pumping it 200 kilometers to the city.
The challenge is not water but political will.
Dr. Stong will discuss Lake Chapala and related water issues as guest speaker at the Open Circle meeting to be held Sunday, April 21, 10 a.m., on the grounds of the Lake Chapala Society.