The Impact of Spatial Variation in Land Use Patterns and Aquifer Characteristics on the Agricultural Cost of Groundwater Conservation for the Southern Ogallala Aquifer

The construction of economic water policy models for irrigated agriculture typically requires simplifying assumptions about the location of groundwater supplies, hydrologic parameters, and land use practices. Even though the hydrologic and economic models are often individually complex, differences in modeling scale often requires aggregating the hydrologic parameters and economic variables to a level that loses important spatial variability. For example, the hydrologic modeling of aquifer depletion by irrigation withdrawals commonly use projected pumping values provided by economic production models that often do not capture the heterogeneous nature of the depth to groundwater and the energy needed to lift the groundwater over time. In a prior study, Das and Willis (2004) linked a spatially disaggregated hydrologic model of the Southern Ogallala Aquifer to a dynamic economic model of agricultural production and found that the failure to accurately account for spatial heterogeneity in aquifer characteristics, overstated both expected baseline agricultural net returns, and cumulative water use over a 50 year planning horizon. This overstatement resulted in an over estimate of conservation cost and cumulative water savings when conservation policy cost and water saving were measured relative to the inaccurate baseline condition. Credible groundwater policy models are needed to sustainably manage the Southern Ogallala Aquifer because annual withdrawals are at least 10 times greater than the natural recharge rate (Guru and Horne 2000). As illustrated in Figure 1, the 42,000 square mile Southern Ogallala Aquifer comprises the southern-most third of the Ogallala Aquifer system.