You don’t need to be a scientist to recognize that Lake Chapala is shrinking at an alarming rate. The untrained eye can see sandy beaches hugging the shoreline getting wider day by day as the water line grows more distant.
In mid-March, the lake stood at just over 43 percent of full capacity, according to official data reported by the National Water Commission (Conagua). It is currently at its lowest level in the past decade, with a surface area of water covering now under 100,000 square hectares for the first time since 2003.
Conagua chalks up the low water level to below average rainfall over the past several rainy seasons, combined with a more rapid rate of evaporation this year. However, data suggests that water retained in upstream dams throughout the Lerma-Chapala watershed may be a contributing factor.
One year ago the Laguna de Yuriria, a man-made lake located in Guanajuato, was literally overflowing, having jumped from 40 percent capacity in mid-January to almost 120 percent in mid-April. Conagua officials attributed that highly unusual dry season upswing to a massive transfer of water from the Lerma River’s giant Solis dam which was undergoing maintenance work. Yuriria has since fallen to 66 percent, but it appears that Chapala got little or no benefit from the excess.
The lake normally loses a meter to a meter and a half of its water level during the dry season, making up the deficit between the months of June and October. Over the 2009-2010 hydrologial cycle the lake dropped 77 centimeters (cm), recuperating 1.56 meters (mt) during the wet months. In 2010-2011, the loss was 1.42 mt, with a scant 24 cm gain. Last season it went down 1.40 mt and recovered only 49 cm.
Another anomaly, so far unexplained by Conagua, is the agency’s data showing the storage volume of the Solis dam on a steady rise, swelling from 20 percent registered last June and to above 95 percent this month, five months after regular precipitation ceased.
On the basis of Lake Chapala’s status, last November the Lerma-Chapala Basin Council announced a modest reduction in surface water allotments to all of the region’s irrigation districts, while maintaining the usual quota for public use in the Guadalajara metropolitan area. More drastic cuts can be expected next fall if the downward trend continues.
Experts estimate that the agricultural sector sucks up as much as 80 percent of the supply, with the remainder divvied up for human consumption, power generation and industry.