While scientists don’t know if California will see more or less precipitation in the future, average temperatures will increase. This will worsen water storage issues for a variety of reasons. 

Warmer winters mean less precipitation will fall as snow and more as rain, which will quickly fill reservoirs and force managers to release water from dams. With less snowpack, flow to reservoirs could slow to a trickle between spring and fall. 

Research also has shown that warming, by increasing evaporation, will cause a devastating 35% flow reduction this century in the Colorado River, one of Southern California’s key sources. 

Rising sea level also threatens freshwater supplies. Seawater could eventually flood Delta pumping stations, spoiling the water supply of millions of people and seeping into coastal aquifers.