EXECUTIVE SUMMARY

The Ojos Negros valley, in Baja California, has been studied from an interdisciplinary perspective, with the principal focus on the relationship between irrigated agriculture and groundwater use, including the environmental and social impacts thereof.            In the past 130 years of recorded history, the valley has undergone a significant social and economic transformation, such that it now represents a substantial entity among the agricultural regions of the state. This change has been positive from an economic and social standpoint; however, the ecological and environmental impacts have been negative.            Irrigated agriculture has resulted in an increase of actual evapotranspiration, as large amounts of subsurface water became part of the surface-water system. Apparently, this has led to a humidification of the local climate, as assessed by a marked decrease (9 oC) in the temperature range during the period of record. The effect is anthropogenic; therefore, it is expected to continue as long as irrigation continues.            In the past 30 years, the increased pumping of groundwater has resulted in a depletion of the water table, which now lies at more than 30-m depth in certain places. The lowering of the water table has negatively affected wetland and riparian ecosystems, which prior to the advent of pumping were quite extensive, and now have been reduced to a fraction of their former size. In particular, the drying out of the Ojos Negros marshes, which gave its name to the valley, is attributed to the depletion of groundwater.            Average water table depletion was forecasted to be 0.4 m yr-1 for the 50-yr planning horizon, assuming present pumping rates (year 2000). This rate of depletion has an effect on the profits of agricultural operations, but the effect does not appear to be substantial, if not for the ejido proprietors, certainly for the agroindustrial companies that operate in the valley. The apparent lack of sensitivity is attributed to the low cost of energy, since the electric tariffs for agricultural groundwater pumping are the lowest. In the absence of appropriate regulation, it is likely that most stakeholders, including ejido proprietors and agroindustrial companies, will continue to operate their agricultural enterprises into the future.            It is certain that the groundwater depletion at Ojos Negros is related to the classical "Tragedy of the Commons." According to this principle, resources held in common will tend to be overexploited by individuals seeking their own gain. Viewed in this light, aquifer regulation appears to be the only way out of this predicament. Regulation should go hand-in-hand with monitoring, since sound policy should always be based on sound data. With regulation, there is an increased chance that the resource will still be there for the benefit of future generations.