Economic Assessment of the Consequences of Ground Water Use

Abstract

The intensive use of ground water throughout the world is directly affecting social and economic development, particularly in those areas where it has been exploited indiscriminately without full knowledge of aquifer potential, causing collateral effects such as progressive lowering of water tables, increased pumping costs, cracking, land subsidence, infiltration of poor quality water, drying up of springs and shallow wells, saline intrusion, decreased river flow, and affecting fragile ecosystems such as deserts and swamps. Proper aquifer management should be considered in light of the many exploitation-related aspects such as physical, social, political, legal, constitutional, and administrative factors. Conjoining so many aspects requires methods of analysis that integrate them systematically such that within a planning process alternatives can be defined leading to the social and economic well-being of the regions dependent on ground water in combination with their other natural resources. Any attempt to solve problems deriving from intensive exploitation of ground water comes to economic considerations whose consequences must be analyzed carefully because of all their implications, both for the rational use of ground water resources and for continuing and/or evolving development of those areas where ground water is being exploited. Within this context mathematical models are the most effective tool for determining the best way to use water resources; in conjunction with the economic aspects of water use, such models enable planners to define what actions, within an optimum investment criterion, will most effectively establish means of control for the proper use of water resources. In the case of the Hermosillo Coast in Mexico, an extensively irrigated area, the main source of supply is a large-capacity granular aquifer (saturated thicknesses varying from 60 to 200 m), with an average annual recharge of 350 Mm 3 that has been exceeded since 1949; exploitation reached a maximum in 1964 of 1137 Mm 3 ; by 1974 agriculture and all collateral economic activities had an uncertain future, the principal effects of overexploitation being sharply lowered water levels in the aquifer, saline intrusion with the consequent reduction of cultivated areas due to abandonment of wells producing salt water, and an inordinate increase in pumping costs. Alternatives were analyzed by a mathematical model that handled a linear program maximizing the annual net benefits obtained from agriculture as a function of the volume of water extracted from the aquifer, which, in conjunction with a simulation model of the aquifer's behavior, permitted determination of the effect on water levels. The results obtained within a 50-year planning horizon gave elements necessary for rational decision-making that have led to a gradual reduction of extraction, changes in crop patterns, improvement of irrigation systems, and more recently, analysis of the possibilities of using waste water from the city of Hermosillo for irrigation and research leading to improvement and planting of halophytes in the coastal zone, ideal for their resistance to high salt concentrations.