Climate Change, Water Resources and Irrigated Crop Yields: A Modeling Framework for Integrated Assessment of the US

While the impact of climate change on rainfed crop yields has been extensively studied, the study of the effect on irrigated crop yields has been more challenging due to competing water uses. By combining a water model and a crop model within the MIT Integrated Global System Model (IGSM) framework (Sokolov et al. 2005), an integrated assessment of the effects of alternative climate policy scenarios on irrigated crop yields is applied to the United States (US). To investigate the issue of water allocation and scarcity for the U.S., we use the IGSM Water Resource System for the US (IGSM-WRS-US) model (Blanc et al., 2013), which draws on the water system module (WSM) developed by the International Food Policy Research Institute (Rosegrant et al. 2008). WRS allows the linkage of WSM with the IGSM. This integrated assessment framework facilitates evaluation of both the direct (via a geophysical model) and indirect (thanks to a computable general equilibrium (CGE) model) impacts of climate policy on water scarcity. Taking advantage of data available for the U.S., we model water at a 99-basin level (instead of the 14 regions in the global WRS model). Detailed economic inputs are supplied by the 11-region U.S. Regional Economic Policy (USREP) model (Rausch et al. 2009). WRS-US models water resources and requirements and allocates the available water to different users each month while minimizing annual water deficits (i.e. water requirements that are not met). To do so, the model solves the allocation of water for each ASR simultaneously for all the months of each year. Upstream basins are solved first. Water resources considered in WRS-US are mainly determined by runoff, which is estimated using CLM. Groundwater resources are estimated based on past uses. Water requirements are estimated for five sectors. Thermoelectric cooling water requirements are estimated using the Regional Energy Deployment System (ReEDS) model (Short et al. 2009) integrated into USREP thro...