Where and When Does Streamflow Regulation Significantly Affect Climate
Change Outcomes in the Columbia River Basin?
Abstract
The Columbia River basin is a large transboundary basin located in the
Pacific Northwest. The basin spans seven US states and one Canadian
province, encompassing a diverse range of hydroclimates. Strong
seasonality and complex topography are projected to give rise to
spatially heterogeneous climate effects on unregulated streamflow. The
basin’s water resources are economically critical, and regulation across
the domain is extensive. Many sensitivity studies have investigated
climate impacts on the basin’s naturalized hydrology; however, few have
considered the large role of regulation. This study investigates where
and when regulation affects projected changes in streamflow by comparing
climate outcomes across 80-member ensembles of unregulated and regulated
streamflow projections at 75 sites across the basin. Unregulated
streamflow projections are taken from an existing dataset of climate
projections derived from Coupled Model Intercomparison Project version 5
Global Climate Models. Regulated streamflow projections were modeled by
the US Army Corps of Engineers and the US Bureau of Reclamation by using
these unregulated flows as input to hydro-regulation models that
simulate operations based on current and historical water demands.
Regulation dampens shifts in winter and summer streamflow volumes.
Regulation generally attenuates changes in cool-season high flow
extremes but amplifies shifts in warm-season and annual high flow
extremes at historically snow-dominant headwater reservoirs. Regulation
reduces dry-season low flow changes in headwater tributaries where
regulation is large but elsewhere has little effect on changes in low
flows. Results highlight the importance of accounting for water
management in climate sensitivity analysis particularly in snow-dominant
basins.