Climate change impacts on water management and irrigated agriculture in the Yakima River Basin, Washington, USA


Vano, J.A., Scott, M., Voisin, N., Stöckle, C., Hamlet, A.F., Mickelson, K.E.B., Elsner, M.M., Lettenmaier, D.P. 2009. Climate change impacts on water management and irrigated agriculture in the Yakima River Basin, Washington, USA. Chapter 3.3 in The Washington Climate Change Impacts Assessment: Evaluating Washington’s Future in a Changing Climate, Climate Impacts Group, University of Washington, Seattle, Washington.


The Yakima River Reservoir system supplies irrigation water to over 180,000 irrigated hectares (450,000 acres). Runoff is derived mostly from winter precipitation in the Cascade Mountains, much of which is stored as snowpack and runs off in the spring and early summer. Five reservoirs within the basin have cumulative reservoir storage of approximately 30% of the river’s mean annual flow. Climate change during the 21st century is expected to result in earlier snowmelt runoff, and reduced summer flows. The effects of these changes on irrigated agriculture in the basin were simulated using a hydrological model driven by downscaled climate scenarios from 20 climate models, output of which was archived by the 2007 IPCC Fourth Assessment Report. In general, we find that the basin transitions to earlier and reduced spring snowmelt as the century progresses, which results in increased curtailment of water deliveries, especially to junior water rights holders. Historically, the Yakima basin has experienced water shortages (years in which substantial prorating of deliveries to junior water users was required) in 14% of years. Without adaptations, for the A1B emission scenarios, water shortages that occur in 14% of years historically increase to 32% (15% to 54% range) in the 2020s, to 36% in the 2040s, and to 77% of years in the 2080s. For the B1 emissions scenario, water shortages occur in 27% of years (14% to 54% range), in the 2020s, 33% for the 2040s and 50% for the 2080s. Furthermore, the historically unprecedented condition in which the senior water rights holders suffer shortfalls occurs with increasing frequency in both the A1B and B1 climate change scenarios. Economic losses include lost value of expected annual production in the range of 5% to 16%, with significantly greater probabilities of annual net operating losses for junior water rights holders.