Lake Chapala is back on a steady rise, gaining in just one month almost the same amount of water it accumulated during the entire short-lived 2011 rainy season.
According to data released by the National Water Commission (Conagua), the lake has taken in 197 billion cubic meters (Mm3) of water since June 18, equivalent to a 19-centimeter boost in elevation. It now stands at close to 50 percent of full capacity, up two and a half points since the rains began.
The agency reports that the lake picked up a paltry total of 23 centimeters between June 24 and August 4 of last year, before dropping 1.40 meters over the subsequent 10-month period. Experts attribute most of the loss to evaporation, with extractions for irrigation systems and Guadalajara’s water supply accounting for around 20 centimeters of the decline.
Typically, the summer rains extend through September and into the early weeks of October. Prolongation of the dry months and scarce precipitation over the last two years translated into steeper than normal yearly dips in the lake’s level and the reduction in water reserves retained upstream in the vast Lerma-Chapala watershed.
Before ever reaching Lake Chapala, the bulk of wet season runoff along the 965-kilometer length of the Lerma River and its principal tributaries is collected in more than 550 dams and reservoirs located in the State of Mexico, Guanajuato and Michoacan.
The system’s 11 largest reservoirs alone have storage capacity to hold 2,054 Mm3 of water, roughly half of the lake’s current volume (3,938 Mm3). At the start of the rainy season they stood at an average of just under 38 percent capacity. As of July 18, the average had inched up to 50 percent, although the Solis Dam, largest of them all, is still less than one-third full.
Under those circumstances, the vagaries of nature will determine whether there will be enough excess supply to significantly pump up Mexico’s largest lake over the next few months. So far this summer Chapala seems to have benefited primarily from direct rainfall and influx from the minor tributaries within its own basin.