A first time study by the Department of the Interior predicts less snow in the California Sierras over the next century due to global warming, potentially hammering drinking water stores for the drier months.

The Sacramento and San Joaquin Basins Climate Impact Assessment, released WHEN, predicts temperatures in California’s Central Valley will rise more than three degrees by the end of the century. That means some precipitation that would normally fall as snow and stick to the mountains will instead wash out as rain.

That snow does more than provide recreation for skiers. It’s like a bank account for future water withdrawals.

"This study confirms that the current status quo for water supply in California is not sustainable," said Deputy Interior Secretary Michael Connor.

Connor said California has relied on having that snowpack to slowly melt, providing water that would last into mid- or late-summer. Less snow means less water in California's hotter, drier months.

Connor said officials are examining two options for capturing and storing that rain: dams for new reservoirs or replenishing groundwater.

Environmentalists oppose new dams.

Last week, Gov. Jerry Brown signed legislation to manage the state's groundwater supply, which until then was not regulated.

Ron Stork, of Friends of the River advocates for limiting how much water farmers pull from aquifers.

The report predicts that's going to happen anyway.

"The average annual agricultural demands are projected to decrease because of reduced irrigated acreage," it reads. The report also predicts increased demand on water supplies from a growing urban population.

The report outlines another problem in meeting those needs: rising sea levels of more than five feet will lead to saltwater intrusion into California’s main water source, the Sacramento-San Joaquin Delta. Increased salinity and a rise in the temperature of river water also means a decline of habitat for fish and wildlife.