Runoff Impacts of Climate Change on Northern California's Watersheds as Influenced by Geology and Elevation - A Mountain Hydroelectric System Perspective

Northern California's Pit, McCloud, Feather, Yuba, and American Rivers each have regional differences that set them apart from the higher elevation, less porous Sierra watersheds to the south. The watersheds from Lake Almanor north are primarily characterized by relatively porous volcanic basalt rock flows with several large springs that provide a large sustained base flow component. Relatively low overall elevation sets these northern watersheds apart as some of the first watersheds in California anticipated to be affected from climate-induced change to snowpack. During an average water year, for much of the Pit and McCloud Rivers, approximately 80-90 percent of river runoff is water from past years that emerge from springs as aquifer outflow. For those rivers that overlay large volcanic aquifers, the form of precipitation has much less significance on runoff timing than watersheds south of Lake Almanor. Climate change is not anticipated to significantly affect timing and quantity of runoff for the basalts, but it will likely have relatively large timing and quantity changes for the Yuba, American, and some reaches of the North Fork Feather River. The Yuba River Basin which has a relatively large proportion of exposed granite in its headwaters is revealing a significant timing shift in runoff into earlier months. This will have effects on hydrogeneration and reservoir operation.