Projections of farmer response to a falling groundwater table : a marriage of economic and hydrological models.

The groundwater problems of central Arizona are illustrative of most of the important groundwater management problems encountered in other arid regions. Large-scale pumpage of underground water for crop irrigation was followed by a rapid decline in the underground water level. Public concern was expressed as to the future of agriculture and other water-using industries in the fact of the falling water table and thus the increasing water costs. Various short- and long-run remedies have been proposed for resolving these problems, including large-scale interbasin water transfers, pumpage limitations, pumpage taxes, and continuation of the present policies without new regulation or augmentation. In order to provide objective criteria for selecting between alternative public policies, it is necessary to project the consequences of each. To do so requires that the interactions through time between the water using sectors of the economy and the physical state of the aquifer be estimated. For this purpose a procedure incorporating dynamic properties into both formal economic and hydrologic models was devised. Previous empirical projections of either hydrologic or economic activity have taken the other activity as largely given. The integrated model is described, the empirical results of 50 year projections for a case study of Pinal County are presented, the results are compared to an earlier study of the same area which used a less sophisticated procedure, and tentative policy implications are drawn.hydrology collectio