Water Trade in General Equilibrium: Theory and Evidence
Abstract
In arid regions, rural-to-urban water markets can reduce shortfalls among high-value urban consumers byallowing irrigators to voluntarily reduce production and sell conserved water. Such sales have been
criticized for reducing economic activity and the availability of water for ecosystem services in the
originating region. However, there are few studies examining the theoretical rationale for such an
argument against water markets, or testing it empirically. In this study, we examine the impact of a 2003
agreement in California to transfer water primarily from the Imperial Irrigation District to San Diego
County, a sale billed as the largest agriculture-to-urban water transfer in US history. We develop a basic
general equilibrium representation of a hydrologic-ecological-economic system to explore the theoretical
effect of this trade on the economy of the water exporting region. The model predicts increases in the
value of water and a decrease in employment, in both high- and low-skill sectors. We test these
predictions using data on agricultural labor and production in Imperial County before and after the
agreement using a synthetic counterfactual constructed using California counties. Post-2003, the
divergence in crop acreage and agricultural production between Imperial County and the control closely
resembles the acreage reduction requirements of the water transfers. The effect also appears in the
agricultural labor market, where we show a decline in the number of both high- and low-skill
employment. Increased crop yields relative to the control also indicate higher water value in Imperial
County in the post-trade period. The increase in value intensified water use, and we document how
greater efficiency by irrigators has decreased flows into the nearby Salton Sea, leading to corresponding
declines in ecosystem services, especially habitat for migratory birds. We conclude with a discussion of
the magnitude of these costs relative to the gains from water trade.