Snowmelt Runoff in the Sierra Nevada and South Cascades during California’s 4th Year of Drought

 For California statewide the 2015 water year, which followed three prior dry years, produced several new hydrometeorological records including but not limited to low runoff, dryness and warmer than normal minimum  temperatures.  The 2015 spring freshet from snowmelt reflected the general lack of snowpack, setting several new records for low spring flows leaving most of California reservoirs less than full.  Headwaters which drained the Sierra’s exposed granites suffered some of the lowest late summer and fall flows on record.  Northern California’s rivers such as the Pit, McCloud, Upper Sacramento, Klamath, and North Fork Feather River above Lake Almanor which have portions of their watersheds overlaying the High Cascades volcanic aquifer systems while at some of their lowest flow rates on record still managed to maintain higher flow rates than for the Sierra exposed granites. While water year precipitation was less than normal, the majority of precipitation occurred in December 2014 with storms delivering the majority of water year precipitation during a couple weeks mostly in the form of rainfall.  A large number of the storms that entered California during the 2015 water year occurred as atmospheric rivers with rainfall occurring on the higher headwater areas of the Sierra.  The relatively high elevation southern Sierra was much drier than northern California, so despite its higher elevation conducive to snowfall, precipitation was among the driest on record, leaving only a shallow snowpack on summits above 2,700-3,300 meters elevation.  Precipitation and unimpaired flows for the past four years were analyzed and compared with prior drought periods to gather perspective as to the severity of the drought.  Years such as the 2015 water year can provide foresight into what California’s late summer and fall mountain flows may look like with continued warming temperatures.  Several studies have indicated a significant reduction in snowpack for California’s mountain areas by the end of the 21st century.  (KEYWORDS: drought, climate change, snowpack, volcanic aquifer systems).