Regulated Rivers: Hydropower Relicensing, Climate Change, and Stream Habitats in the American West

Hydropower relicensing provides an opportunity to evaluate tradeoffs between water (and water quality) for the environment and water for hydropower in regulated rivers. Climate change is currently not considered with hydropower relicensing, although it is anticipated to change hydropower generation, instream water quantity, and water quality. Coupled hydroclimate modeling was used to evaluate changes in hydropower generation, instream flows, stream temperatures, and riparian systems in California’s Sierra Nevada Mountains with projected hydropower operations and climate warming. Modeling suggests that climate warming will reduce hydropower generation, and competition for water for hydropower, environmental flows, and other competing water uses will likely increase. Stream temperatures are anticipated to rise, although managing the hypolimnion (cold water pool) of large reservoirs for downstream temperature management shows promise for maintaining cold water habitats throughout this century. The spring snowmelt recession is fundamental for maintaining both stream channel shape and riparian ecosystems, although both hydropower generation and climate warming (snowfall shifting to rainfall) change the timing, magnitude, and rate of change of the snowmelt recession. This research shows that considering climate change for the 30-50 year duration of hydropower licenses would establish more robust hydropower generation operation conditions, in turn improving mechanisms to maintain instream and riparian systems in regulated rivers