Under a presidential decree put into effect last month, the distribution and exploitation of surface water resources throughout the vast Lerma-Chapala watershed will henceforth be managed under a formalized set of regulations that ostensibly provide a legal shield for Mexico’s largest lake.
The document published in the Official Gazette of the Federation on April 8 establishes a ban on the issuance of new permits for surface water use anywhere within 19 catchment areas located the Lerma-Chapala hydrological region. It also sets a per annum ceiling of 5.12 billion cubic meters (5,122.9 Mm3) on the total volume of allowable extractions, including liquid lost to evaporation.
Technical studies indicate that demand for surface water exceeds availability by an average of 677 Mm3 each year. To counteract the deficit, the regulatory code spells out specific terms to be applied to all users currently entitled to surface water allotments, including irrigation farmers who suck up the largest portion of water resources.
Yearly usage quotas follow mathematical formulas based on seasonal measurements of precipitation and calculations on the amount of water stored in reservoirs and Lake Chapala at the start and finish of each rainy season. Severe cutbacks will be applied if the lake falls to around 15 percent holding capacity on June 1 or stands at 25 percent or less on November 1.
However, lake experts suggest that the decree lacks vigilance and enforcement guidelines that might have put real teeth into the water management agreements and policies that have been followed on a goodwill basis since 1989.