Hydrology of the Lerma-Chapala Watershed

Abstract

Hydrologically speaking, the Lerma-Chapala watershed is a sub-basin of the Lerma-Santiago watershed, with a total area of 137,144 km2, comprising the Lerma and Santiago rivers and Lake Chapala as an internal lake, which forms the boundary between the two river basins. The Lerma river basin, which is considered to end in Lake Chapala, has an area of 52,545 km2. The mean annual precipitation over the entire Lerma watershed is about 730 mm. Hurricanes and other cyclonic perturbations regularly affect the Lerma river basin and floods occasionally cause damages in the area. The dominant climate in the watershed is subtropical, ranging from sub-humid to arid. The Lerma river is more than 700 km long and receives water from several tributaries. Some of the more important are the Laja, Turbio, Angulo, and Duero rivers. Besides Lake Chapala, there are several important natural lakes, like Patzcuaro, Cuitzeo and Yuriria as well as a significant number of dams. The main use of these dams is for irrigation purposes of about half a million hectares. The mean annual runoff of the Lerma river to Lake Chapala is about 1,160 Mm3, although this figure varies considerably from year to year depending on several factors, among which variations in water extracted from the Lerma river is the most important. About 1,000 Mm3 are extracted from the numerous aquifers in the basin, among which the Toluca, Ixtlahuaca, Queretaro, Leon, Penjamo, Aguascalientes and Cueramaro aquifers are among the most important. They serve both urban and agricultural water needs. In general, groundwater resources in the basin are overexploited.