UC Santa Barbara

The Colorado River basin has been the subject of numerous studies covering a wide range of issues. Nevertheless, some areas require further analysis, such as the lowest part of the Colorado River basin, where lies the Mexicali Valley of Baja California, Mexico. The purpose of my thesis is to estimate the amount of water used in this valley and assess whether there is water deficit that could degrade the valley’s aquifer.

Due to the difficulty of obtaining official data about water usage, this author estimated the annual farming water using Remote Sensing and Landsat imagery and the NDVI index, classified and determined the area of each main crop group in the Mexicali Valley. These areas were multiplied by the average water use by crop for the 2017-2018 water year. The Mexicali aquifer supplies drinking water for cities, communities, and industries. I calculated this water use according to the population size and from Mexican specifications for water supply and added to the farming use to calculate the total water use in Mexicali Valley. The results of this independent method were compared with official (that is, from the Mexican government) data to determine, relevant differences and important coincidences. The most important difference concerns the estimate of the amount of water recharged to the aquifer considered in the formulation of a valley-wide water balance. The major coincidence was the existence of a critical water deficit and the associated groundwater depletion, which threatens negative effects to the aquifer such as land subsidence, risk of pollution, seawater intrusion, and water insecurity.

Compounding the water deficit in the Mexicali Valley is the long drought in the Colorado River basin and the proposed reductions in water allocation for all the States in this watershed. Climate change models are predicting less water for the Colorado basin, which could bring even stronger water restrictions in the short term. The State (Baja California) and Federal water authorities in Mexico must develop a drought contingency plan to cope with the worsening water scarcity in the Mexicali Valley. This would require unprecedented and unpopular law enforcement, yet it would help avert a major water crisis in the California-Mexico border region.

The Mexicali Valley aquifer case demonstrates the fragility of relying on intensive groundwater exploitation for crop production in arid regions. Food production and food security must consider the sustainability of this type of irrigation systems in similar geographical settings. We must use groundwater strategically since it is a renewable yet exhaustible resource.