Water Resources Research Act Program

Details for Project ID 2011ID168B

Modeling Dynamic Feedback between Surface and Groundwater Systems: Implications for the Economics of Conjunctive Management

Institute: Idaho
Year Established: 2011 Start Date: 2011-03-01 End Date: 2013-02-28
Total Federal Funds: $10,000 Total Non-Federal Funds: $20,372

Principal Investigators: Kelly Cobourn

Project Summary: A key feature of hydrologically connected surface and groundwater systems is two-way exchange between the systems. In a recent article, Taylor, Contor, and Hamilton (2010) explain the way in which that exchange depends upon human decisions concerning water use. In the surface-to-groundwater direction, the management of irrigation water heavily influences the rate of seepage and groundwater recharge. In addition, the use of groundwater influences the water table, determining the rate of seepage from surface to groundwater systems. In the groundwater-to-surface water direction, groundwater pumping and aquifer draw-down influence the rate of discharge via springs or seeps. The nature of the feedback between surface and groundwater systems, while understood by hydrologists, has received little attention in the economic literature. The objective of this project is to examine the way in which the hydrologic feedback loop between surface and groundwater systems affects irrigator decisions and the implications in terms of the economic benefits (or costs) of jointly managing the two systems. To accomplish this broad objective, the proposal involves three intermediate objectives. The first is to specify a baseline model of the linked surface-groundwater system that will be used as the foundation for an economic model of irrigator behavior. To do so, the project will examine the qualitative characteristics of the feedback loop between surface and groundwater systems, including recharge, discharge, and the relationship between the water table and the rate of recharge. The second intermediate objective is to build upon the biophysical framework to create a model of irrigator behavior that reflects withdrawal and irrigation decisions by both surface and groundwater users. The third intermediate objective is to determine the water use decisions made by irrigators under the status quo and under conjunctive management. The economic outcomes under different policy scenarios will be compared to quantify the benefits or costs of conjunctively managing connected surface and groundwater systems. Because of the inherently dynamic nature of the hydraulic exchange between surface and sub-surface systems, the project will employ an optimal control modeling approach. As a first stage, the model will approach the problem from a system-wide perspective, treating surface and groundwater users as aggregate groups that choose how much and when to withdraw water for irrigation, given the current state of irrigation technology. A second stage disaggregate modeling approach will reflect the spatial dynamics of the feedback between surface and groundwater systems. Specifically, the model will differentiate the way in which the relative location of surface and groundwater withdrawals and irrigation applications affects the timing of recharge and discharge. This modeling effort contributes significantly by addressing a policy issue of immediate importance within Idaho and by contributing to a gap in the economic literature. The proposed model is inspired by and reflects key features of the conjunctive management problem facing irrigators in the Eastern Snake Plain. It will provide insight into the potential magnitude of the economic implications of alternative water management policies. This is particularly salient in Idaho given the recent stresses on water resources and anticipated shortages in the future due to changing climatic factors. With respect to the economic literature, the feedback between surface and groundwater systems has yet to receive rigorous attention. Further, the second-stage spatial-dynamic model of irrigator behavior is at the methodological forefront of the field of applied economics (Smith, Sanchirico, and Wilen 2009). This project leverages existing research funded by the Idaho EPSCoR award EPS-0814387.