How are Regional Water and Energy Cycles Affected by Improvements in Irrigation Efficiency?

Climate change is expected to increase the frequency and severity of droughts in many parts of the world. Farmers are likely to adapt their practices to reduce drought-related impacts; investment in more efficient irrigation technologies is considered an effective way to improve farm-level water-use efficiency. Switching to a different irrigation system will alter latent heat fluxes through a change in the partitioning between evaporative, runoff and deep percolation losses of applied irrigation water. This change in partitioning between evaporative and non-evaporative losses potentially impacts not only crop productivity, but the local climate as well. We focus this case study on Washington State’s Yakima River Basin (YRB) because 1) it is an area of inefficient irrigation systems, and 2) it already experiences drought impacts regularly and is projected to experience more frequent and severe droughts in the future, particularly as it is a snow-melt dominant watershed that is vulnerable to warming impacts on summer water availability. To simulate the investment pattern and its effects on regional water and energy cycles, we developed a modeling platform that integrates climate, hydrology, agriculture, and human decision making processes. We utilize a computational modeling framework that includes a tightly coupled hydrologic-agricultural model (VIC-CropSyst), a process based irrigation module, a river system model (YAK-RW) and an economic model. Results suggest potential significant shifts towards more efficient irrigation systems; this shift increases the irrigation evaporative losses and reduces reusable irrigation return flow, which further modifies regional water availability and the spatiotemporal patterns of water and energy fluxes over irrigated areas. Results improve our understanding as to how human adaptations to climate change can feed back to impact local climate dynamics.