Assessment of uncertainties on the impact of climate change on water resources management using an integrated Earth System Model: application over the Snake River Basin

Multiple climate change impact assessments have been performed over hydrology, water resources management and crops models, using downscaled climate change meteorological forcing to force a hydrology model which in turns forces a crop model and a water resources management model. Most of the time, the chain is integrated but without feedback between the components. For example the impact of climate change on crop is assessed assuming no change in irrigation supply. The effect on water resources management is assessed assuming no change in irrigation demand and using existing operations rules for optimization. Both crop and water resources management models assume negligible effect of their redistribution of water resources in space and time over evapotranspiration fluxes and consequently feedback into the atmosphere. The Community Land Model has been updated with an improved routing model (MOSART) that integrates a water resources model using generic reservoir operations. Those generic operations are calibrated using unregulated flow and irrigation demand of a recent retrospective period. We estimate the uncertainty in climate change assessment on the water resources management over the Snake River Basin, USA by comparing regulated flow , irrigation demand and irrigation supply when using the integrated Earth System model with future climate calibrated with i) past flow and demand characteristics and ii) future flow and demand characteristics.