Water Always Wins

In late 2016, just as the thirst was growing truly desperate, the atmospheric rivers arrived. These enormous trains of condensed vapor move from west to east across the Pacific like rivers in the sky, 1,200 to 6,000 miles long and capable of carrying fifteen times the average flow at the mouth of the Mississippi. When they hit mountains in California, they can dump hurricane quantities of rain. Storms borne on atmospheric rivers are not new in the state, but they are increasing in frequency worldwide, likely doubling by the end of this century. And as Earth continues to warm, models show that atmospheric rivers in California will hold an estimated 10 to 40 percent more water, increasing the risk of floods and mudslides. Fifteen of these strong atmospheric rivers hit California during the winter of 2016–17, turning hillsides so sodden that they slid down over roads.