Half of the country is currently in some state of drought. In California right now, the entire state is in a state of drought. But despite what you may have read, neither of those particular points of data is cause to panic.
All of which came to mind when looking at this "explainer" on the drought from Vox's Brad Plumer entitled five horrifying maps of America's massive drought".
The first of the five horrifying maps in the piece shows current drought conditions in United States, using data from the excellent U.S. Drought Monitor. (If you're curious how the level of drought is calculated, read this.) Sure enough, half the country is in drought.
But, then, half the country has been in drought for half of the weeks since January 2000. Yes, we're looking only at an era in which global warming already exists (we aren't comparing now with, say, 1920), but the current level of national drought isn't remarkable. It isn't even remarkable for May. In the majority of years since 2000, more than half of the country has been in drought during May.
Plumer's second map shows just California. "100 percent of California is now in drought," its headline reads. The word "now" there is subjective. "Now" extends back to the middle of February, since which time there's been no drought in California for only two weeks — during which the level of drought was 99.99 percent. Since January 2000, California has been entirely engulfed in drought 68 of the 750 weeks — nine percent of the time.
The actual problem right now is noted by Plumer, a little further down. "[E]very single part of California is now facing 'severe,' 'extreme,' or 'exceptional' drought," he writes, "the first time that's happened in the [Drought Monitor]'s 15-year history." The drought is substantially worse than past droughts. That's the problem. And that is exactly what we'd expect to see in a warming world.
Drought, like other weather phenomena, fluctuates. At the bottom of this post is a graph of how the United States has experienced drought since 2000. The darker the red, the higher the severity of the drought. What climate models predict is that — slowly! — we'll see longer, more severe droughts in some parts of the country, like the west. It's the severity of California's drought that makes it exceptional and dangerous.