TY - Generic T1 - Snowmelt Runoff in the Sierra Nevada and South Cascades during California’s 4th Year of Drought T2 - 84th Annual Western Snow Conference Y1 - 2016 A1 - Gary J. Freeman AB -

 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).

JF - 84th Annual Western Snow Conference CY - Seattle, Washington UR - /files/PDFs/2016Freeman.pdf ER - TY - Generic T1 - The 2014 California Drought - Dealing with Extreme Dryness From A Hydroelectric Planning Perspective T2 - 82nd Annual Western Snow Conference Y1 - 2014 A1 - Gary J. Freeman KW - climate change KW - drought KW - hydroelectric KW - reservoirs KW - Sierra AB -

The 2013 calendar year was the driest year on record for California. For San Francisco based Pacific Gas and Electric Company (PG&E), which operates the largest investor owned hydroelectric system in the United States, the water management planning challenges, which were encountered during the first three months of 2014 and the twelve unusually dry months preceding 2014 were unlike those of earlier droughts. The acceptance of both the concept of climate change impacts as well as new paleo-climatological research findings about California and the southwest were for the first time being given serious consideration in the Company’s water release planning. The prospect that the persistent high pressure region blocking the storm track into California fromthe Eastern Pacific and Gulf of Alaska could possibly remain “parked in place” became a principal scenario needed for effective planning. In terms of snow water equivalent (SWE), the February 2014 statewide snow surveys were less than 15% of the historical February 1 average. The demands on downstream water release requirements for maintaining biological flows, whitewater rafting, and other recreational opportunities have continued to increase in the past 38- 39 years from the 1976-1977 drought, which were two successive very severe dry years. Conditions leading into the 2014 drought included 15-years of generally declining wetness over much of California causing the northern California’s porous volcanic aquifer storage to decline significantly from the aquifer’s relatively high mid-1990’s storage state. Also water year runoff from rain-shadowed areas of the northern California’s Sierra and southern Cascades have been in a state of trending decline since the 1976-1977 drought, a condition likely attributable to impacts from climate change. Utilizing the latest research findings available in 2014 on climate change and drought, the approach to reservoir and power production planning at PG&E changed from that utilized with prior droughts. Rather than assuming median likelihood or some low level of exceedances probability for remaining seasonal precipitation, the planning would take place as if the high pressure system pattern would continue to persist with no additional runoff expected.

JF - 82nd Annual Western Snow Conference T3 - Proceedings of the Western Snow Conference CY - Durango, Colorado UR - sites/westernsnowconference.org/PDFs/2014Freeman.pdf ER -