Informing sustainable irrigation management strategies in response to implementation of Washington State’s Yakima Basin Integrated Plan (YBIP)

Abstract:

As an important agricultural snowmelt-dominant watershed in the Pacific Northwest region of the United States, the Yakima River basin (YRB) is projected to experience increasing water scarcity problems during the summer irrigation season. The system is already experiencing over-allocation with unmet irrigation entitlements occurring more frequently, resulting in negative consequences to YRB agriculture and therefore the economy of the region. Water storage management is one climate change adaptation strategy particularly applicable to snowmelt-dominant watersheds experiencing a shift of its water availability away from the summer irrigation season. These changes in conjunction with climate change will significantly change the availability of water for agriculture, thus impacting farmers’ irrigation decisions. These decisions occur at multiple time scales, including capital investment to change irrigation technology (decadal), to distributing the seasonal allocation of water in a projected drought year (seasonal), to deficit irrigating crops (daily to weekly).

The Yakima Basin Integrated Water Resource Management Plan (YBIP) aims to improve the availability of water for agriculture, fish, and communities through a number of projects, including additional or modification of physical infrastructure. Our objective is to reduce the vulnerability of irrigated agriculture in the YRB to climate change through exploring changes in irrigation management strategies in response to implementation of each phase of YBIP. We apply VIC-CropSyst (a newly coupled hydrological/cropping model) and Yakima RiverWare (a water management model) to explore the relationships between climate, hydrology, crop growth and phenology, irrigation management, and YBIP implementation. Results suggest the importance of irrigation management strategies in YRB and indicate that if irrigation strategies are modified in response to changes in physical infrastructure, significant enhancements to instream flow and agricultural water availability will minimize the adverse impacts of climate change.