Future droughts in California are likely to bite deeper and last longer than the one now gripping the state, according to new research into the potential effects of climate change.

Scientists from the Scripps Institution of Oceanography and the U.S. Geological Survey used computer climate modeling tools to estimate the effects of warmer temperatures in future decades. In particular, they studied the effect on California’s mountain snowpack, the largest source of fresh water in the state, which refills thousands of water-storage reservoirs each spring via snowmelt.

The results show that by 2050, the median snowpack present on April 1 each year could be one-third smaller than the historical median, and by 2100 it could be two-thirds smaller. Such a dramatic loss of snowmelt would produce less runoff to refill reservoirs each summer, potentially making droughts an ever-present condition.

“The water contained in the snowpack is declining pretty steadily through the 21st century,” said Dan Cayan, director of the California Climate Change Center at Scripps in San Diego and the study’s lead author. “According to the models, we’re already detecting these changes in snowpack.”

California water management officials are bracing for these potential changes. On Thursday, the state Department of Water Resources released a revised California Water Plan, a comprehensive strategy to protect the state from water shortages and floods that looks out to 2050. A major focus involves managing the effects of climate change.
“Unless we take strong action, we won’t have the existing water be reliable for the future,” said John Laird, secretary of the California Natural Resources Agency, which oversees DWR. “Over time, conservation as a way of life in California is something that simply has to be done.”

DWR’s water plan lays out 350 strategies aimed at boosting water supplies and improving conservation. Key among them is better connecting existing water systems. For instance, the plan calls for reconnecting rivers with their historic floodplains so that, when floods occur, the water can be held on the land to recharge groundwater wells.
In many cases, this would mean breaching levees. It also could mean difficult changes in land use, said DWR Director Mark Cowin.

“For many decades, one of the challenges we’ve had is that agencies that carry out responsibility for water management are not necessarily connected to the local agencies that are responsible for land use,” Cowin said. “That needs to change.”

Because of the way reservoirs are operated today, it is difficult to capture all the runoff from rainfall that occurs in winter. Most large reservoirs are required to maintain a certain amount of empty space at all times during winter to ensure there is room available to capture potential floodwaters. In the days and weeks after every storm, water is slowly released downstream to maintain that empty space.

A relatively new concept called “forecast-based operations” could be applied instead, which would allow reservoirs to hold more water in storage when storms are not expected. But it has been slow to evolve and is not yet formally in use at any major California reservoir.

Changing reservoir rules is not simple, because the state’s reservoirs serve many purposes. The changes could increase flood risk, alter wildlife habitat and diminish recreational opportunities.

DWR’s Cowin said a broader rethinking of California water systems is needed to account for climate change as well as population growth. The state’s population, at 38 million, already exceeds all other Western states combined. By 2050, it is projected to increase 30 percent, to about 50 million people.

Serving all those people in a warmer future would mean changing the rulebook at every reservoir, along with increasing water supplies through conservation, wastewater recycling, groundwater storage and other measures.
All this will cost money. The California Water Plan estimates the state needs to invest $200 billion over the next decade simply to maintain current levels of service, and another $500 billion in future decades to make improvements. Those numbers include all levels of government spending, from local water districts to the federal government.

http://www.sacbee.com/news/local/environment/article3505269.html