Global warming impacts are expected to wreak havoc on hydropower output in California and the West because of lessening snow pack as well as earlier and heavier snow runoff, speakers warned during a California Energy Commission April 7 workshop on climate change and energy. California has far more hydropower than the national average, with 22 percent of its power produced by falling water compared to seven percent nationally. Models show that less precipitation and earlier spring melt may mean about 20 percent less runoff, 19 percent less generation, and 12 percent less revenue, according to Jay Lund, University of California, Davis, professor of environmental engineering. By mid-century, a one-third loss in the springtime snow pack in the Sierra Nevada Mountains is estimated, with it dropping by half by the end of this century, said Dan Cayan, with the Scripps Institute of Oceanography at the University of California, San Diego. In addition, reduced hydropower imports from the Colorado River are anticipated. A drop in snow levels in the high Sierra means lower water storage in the higher and lower elevation reservoirs that fuel hydropower and also feed Central Valley agriculture. Making matters worse, is that the expected higher temperatures caused by large amounts of carbon in the atmosphere will drive up energy use, in particular air conditioning use in toasty regions during the hottest times of the day. Gary Freeman, water team manager for Pacific Gas & Electric, which owns and operates 4,000 MW of hydro in the state, said the utility was somewhat protected from climate change. A significant amount of the water supplies in some reservoirs come from groundwater. Supplies in key reservoirs are made up of about 38 percent groundwater, 37 percent from snow pack and 25 percent from rainfall. However, Freeman added, \u201cThat ratio will be changing, creating risks for the hydroelectric system.\u201d \tAir conditioning use is responsible for one-third of the peak demand on hot days, with two-thirds of that driven by residences. Southern California, Sacramento, and inland areas likely will see higher temperatures, particularly in the summer because of the overheating Earth. Climate change could cause energy use to soar by up to 20 percent by the end of the century, said Maximillian Auffhammer, University of California, Berkeley, assistant professor of agricultural and resource economics. In addition, instances of extreme heat events are predicted to increase, with the heat lingering longer. Another stress on the electrical system is groundwater pumping. As water supplies from rivers and streams diminish, agricultural interests, which use a large share of the state\u2019s water supply, will start tapping groundwater as a replacement. Accessing groundwater supplies requires pumping, which will further drive up energy demand. \u201cIt will get harder and harder to adapt,\u201d noted Cayan. Getting more play these days in climate change discussions is the need to both take steps to cut carbon emissions and adapt to warmer temperatures. One adaptation option is to increase the storage level of reservoirs to be able to hold more rainfall and higher and earlier runoff. However, that strategy is very costly. In addition, how global warming will impact rainfall is a big unknown. Thus, reservoir operators will have to cope with significant uncertainty, the speakers warned this week. Given shrinking hydropower resources and the ever increasing cost of natural gas to fuel peaker plants, pumped storage projects are seen as an attractive option. These projects pump water uphill to a reservoir during off peak energy times. The water is then released during times of highest demand and highest energy prices. Making matters more difficult is the dueling interest of those who operate reservoirs for flood control versus hydropower and water supply managers. Flood control operators want lower reservoir levels to make more room for water from heavy precipitation events to avoid or minimize flood damage to vulnerable areas, like Sacramento. In contrast, hydropower operators want high water levels held behind dams to maximize hydropower output during peak demand periods to increase profits. Given that California swings between floods and droughts, the hydrological system already is at its limit. Under historical conditions, snow pack from the Western Sierra, which feeds numerous reservoirs, already varies annually by up to 40 percent of so-called average years.