Climate and Management Alternatives in Snake River Basin Nathan VanRheenen and Richard N. Palmer Dept. of Civil and Environmental Engineering University of Washington

Goals of Research How can the potential impacts of climate change be best mitigated? Goal 1: Develop a model that provides a “constrained optimal” management strategy for Snake River Basin users Goal 2: Incorporate Mid-range forecasts into optimization to guide operations  New starting point for policy-makers Optimization Model of SRB (SIRAS) can serve to illustrate upper bound of benefits associated with management

SIRAS Considers Major surface water features System uses e.g., flood control, irrigation, fish, hydropower Groundwater impacts 8 major irrigation districts Economic Objective Function

SIRAS - Approach LP/SLP Decomposition Objective Function Weekly timestep Maximize Z = Agriculture profit ($) + Hydropower profit ($) - Flood damages ($) - Environmental Target Penalties Subject to Inflows, PET Water rights Groundwater availability Farmland availability, crop values and costs, irrigation efficiency Energy demand and rates Infrastructure limitations (reservoir and powerplant capacity, etc.) Network flow constraints

SnakeSim Operations Model VIC Hydrology Model Changes in Mean Temperature and Precipitation or Bias Corrected Output from GCMs SIRAS Optimization Model

SnakeOpt – Decomposition Approach Run model from Rolling 5-year window Step 1 Maximize over 5 years (260 mo.) Extract conditions at week 52 Redefine constraints Rerun first 52 weeks to determine first year model optimum Step 2 Move to 2 nd 5-year window Redefine constraints with Step 1 end conditions Proceed with 2 nd window as per Step 1

Step 1: Optimize over 5 years Step 2: Extract year 1 ending conditions Step 3: Redefine conditions as constraints Step 4: Optimize year 1 only with new constraints Step 6: Move to next rolling 5-year block and repeat Steps 1-5 Step 5: Initialize year 2 starting storage and gw responses Year 1 Year 2 Year 3 Year 4 Year 5 Year 2 Year 3 Year 4 Year 5 Year 6 End Storage Total Power Irrig Area GW Response End Storage GW Response SIRAS Approach – LP/SLP Decomp

Implications Why isn’t the system operated like this now? Historical precedent Snake River managed as 2 distinct rivers Irrigators get the “first fruits” Extensive surface irrigation in the upper river is necessary to ensure high flows (vis-à-vis groundwater discharge) in the lower river

Mid-term Optimization Forecasting system offers opportunities for informed and science based decision making Mid-range forecasts provide improved river forecasts Operating suggestions can be updated as conditions change over the season Economic objective functions can be modified Operation relationships of Snake relative to Columbia River can be evaluated

Integration Integration will occur at several levels Output of optimization model will be more fully tested in SnakeSim to test robustness Water Markets research effort will provide realistic constraints on transfers Long-term forecasts will be incorporated into optimization model