A System Dynamics Model for Conjunctive Management of Water Resources in the Snake River Basin

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The Pacific Northwest is expected to witness changes in temperature and precipitation due to climate change. In this study, we enhance the Snake River Planning Model (SRPM) by modeling the feedback loop between incidental recharge and surface water supply resulting from surface water and groundwater extraction for irrigation and provide a case study involving climate change impacts and management scenarios. The new System Dynamics-Snake River Planning Model (SD-SRPM) is calibrated to flow at Box Canyon Springs located along a major outlet of the East Snake Plain Aquifer. A calibration of the model to flow at Box Canyon Springs, based on historic diversions (1950-1995) resulted in an r2 value of 0.74 and a validation (1996-2005) r2 value of 0.60. After adding irrigation entities to the model an r2 value of 0.91, 0.88, and 0.87 were maintained for modeled vs. observed (1991-2005) end-of-month reservoir content in Jackson Lake, Palisades, and American Falls, the three largest irrigation reservoirs in the system. The scenarios that compared the impacts of climate change were based on ensemble mean precipitation change scenarios and estimated changes to crop evapotranspiration (ET). Increased ET, despite increased precipitation, generally increased surface water shortages and discharge of springs. This study highlights the need to develop and implement models that integrate the human-natural system to understand the impacts of climate change.