TY - Generic T1 - Planning Beyond California's Three-Year Drought - A 2015 Hydroelectric Planning Perspective T2 - 83rd Annual Western Snow Conference Y1 - 2015 A1 - Gary Freeman KW - climate change KW - drought KW - hydroelectric KW - reservoirs KW - Sierra AB -

Following three dry years, precipitation for the month of December 2014 was 131% of the Sierra Region’s 120-year December average; however October-December 2014 as a 3-month period continued to remain below average. On December 31, 2014, precipitation for the California Department of Water Resources (DWR) northern California 8-station index was 129% of its historical 30-year average. However DWR’s southern California 5- station index was only 70% of its 30-year historical average. Precipitation was much above average in northern Sierra and drier than average for the southern Sierra. In spite of this unbalanced situation statewide, the overall increase in precipitation appeared to many as a dramatic turnaround from one of the most severe droughts in California’s recorded history. However, in spite of this dramatic precipitation recovery, California’s snowpack at the end of December statewide was only 49% of average, thus remaining much below average, mostly due to the higher snowline accompanying the relatively warm December storms. For Pacific Gas & Electric Company which has historically produced about 38 percent of its conventional hydroelectric energy from the aquifer outflow of large volcanic springs in northern California and approximately 37% of its conventional hydroelectric energy from the snowpack, the fall rains after satisfying an unusually large soil moisture deficit made little difference in the outflow rates and added only meager amounts of recharge to northern California’s porous volcanic aquifer storage which had lost approximately four million acre feet from underground storage since 1999. The 2014 calendar year was highly unusual beyond its single characteristic of being dry. Minimum daily temperatures for the 12-month period for the Sierra Region were the warmest in 120 years of record. This additional heating resulted in some of the driest soils moisture conditions for California in the past 1200 years. While rain dominated precipitation caused flood damage in December for parts of California, river flows quickly declined following the December rains. Aquifer outflows in northern California continued to remain much below normal following December’s wetness. As of January 1, 2015, precipitation for the remainder of the water year would need to increase to about 135% of average to get 100% of average annual conventional hydro generation.

 

Presentation in PDF

JF - 83rd Annual Western Snow Conference T3 - Proceedings of the Western Snow Conference CY - Grass Valley, California UR - /files/PDFs/2015Freeman.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 - TY - Generic T1 - Analyzing the Impact of Climate Change on Monthly River Flows in California's Sierra Nevada and Southern Cascade Mountain Ranges T2 - 80th Annual Western Snow Conference Y1 - 2012 A1 - Gary J Freeman KW - climate change KW - hydroelectric KW - orographic KW - subbasin KW - unimpaired flow AB -

The impact of climate change on monthly river flows in California's Sierra Nevada and southern Cascade Mountain Ranges and its potential to impact hydroelectric production was analyzed to determine changes that have taken place in two successive 35-year periods during the past 70 years. Unimpaired monthly flows from both California's Department of Water Resources' (CDWR) Data Exchange Center's (CDEC) files and from Pacific Gas and Electric Company's (PG&E) operational subbasin runoff forecasting files for the Feather River were analyzed for comparison of the two periods. A notable change was the shift of snowmelt runoff from the April through July period into the month of March. March flows were larger for the more recent 35-year period for all of the flow points analyzed in the Sierra and southern Cascades including two subbasins on the upper North Fork Feather River where rain shadowed climate change impact has significantly reduced both snowmelt and water year runoff in the more recent 35-year period. The increase in March runoff appears to be a combination of mostly earlier snowmelt due to warming temperatures and from an increase in proportion of March precipitation that now occurs as rainfall. In northern California both the shift of snowmelt into March and the reduction of snowpack overall has resulted in reduced late spring and summer flows during the months of April through June. Subbasins south of the Yuba River have for the most part increased overall snowmelt runoff for the March 1 through July 31 period, while subbasins from the Yuba River north have remained either equal or declined in snowmelt runoff in recent years. Both increased elevation and orographic cooling seem to be critical for delaying the impacts of climate change on affecting spring and early summer runoff. For a rain-shadowed subbasin such as Lake Almanor, the recent 35-year period shows a 22% decline in the April through July runoff caused primarily from a combination of: 1) earlier snowmelt, 2) increased proportion of precipitation occurring as rainfall in recent years with less snowfall overall, and 3) reduced aquifer outflow from springs. (KEYWORDS: climate change, subbasin, unimpaired flow, orographic, hydroelectric)

JF - 80th Annual Western Snow Conference T3 - Proceedings of the Western Snow Conference PB - Omnipress CY - Anchorage, Alaska UR - sites/westernsnowconference.org/PDFs/2012Freeman.pdf ER -