It is now certain that drought will continue for another summer in many parts of California. On Monday, Gov. Jerry Brown issued an executive order making many water-conservation requirements permanent, and calling for stricter measures to be imposed through January 2017.

Most of us have never experienced a drought that lasted this long, and many Californians now wonder: how much worse can it get?

Benjamin Cook has some insight on that. Cook is a research physical scientist at NASA’s Goddard Institute for Space Studies in New York, and he has a Ph.D. in environmental science from the University of Virginia.

Last year, Cook was the lead author on a study published in the journal Science Advances that examined the risk of future droughts. Using computer models of future climate change and analyzing tree-ring growth patterns, the study found that the latter half of this century is likely to be drier than at any time in the past 1,000 years. 

Research by NASA scientist Benjamin Cook has found that if we continue on our “business as usual” approach to climate change, then we’re likely to face a high risk of megadrought in the American West. (Benjamin Cook)

A key feature of the study is not just precipitation, but temperature and soil moisture. These are equally powerful measures of drought that are often overlooked. Cook found that even though precipitation is expected to increase slightly over parts of California in the future, droughts will still be worse because climate change will make the state hotter, thereby reducing soil moisture. This will create what the study calls “a level of aridity exceeding even the persistent megadroughts that characterized the Medieval era.”

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