California has been in drought for some time now, visible in California data for the Palmer Drought Severity Index, or PDSI. It’s a measure of, well, drought severity. On the PDSI scale negative numbers mean drought (i.e. unusually dry conditions) while positive numbers mean unusually wet conditions, so it’s the most extreme negative PDSI values that mark the most extreme drought. Anyway, here are 12-month moving averages of the data through April
Much of the cause of the drought is reduced precipitation for many years now. But similar reductions have been felt before, without leading to such severe drought. What’s different this time is that in addition to reduced precipitation, California has been feeling the heat.
Here are 12-month moving averages of temperature in California:
Not only have the drought years been exceptionally hot, temperature has recently soared to new heights.
Conservation measures are already in place, with extreme water rationing not far behind. One of the problems is that even during “normal” years, there’s precious little rainfall in most parts of California during most of the year. Winter is the “wet season,” so no relief is in sight — at least in terms of precipitation — for most of the rest of this year.
Worse yet, the usual sources of water for Californians, which get them through the most-of-the-year dry season, are also in bad shape. One of (perhaps the) most important sources is snowmelt, from the accumulated snowpack in the Sierra Nevada mountains. But the precipitation deficit hasn’t just hit rainfall, it’s also notable in snowfall, so this year the snowpack has reached record lows.
That situation is made worse by high temperature, which not only increases evaporation (and therefore drought), it also melts the snowpack earlier and faster. One measure of its overall effect is the total snowpack on April 1st of the year. This year it sank to a new low, a mere 8% of its normal value.
It’s even more obvious on a plot which may itself be more relevant, a log-transformed plot:
Yes, the drought in California is the worst we’ve seen.
Yet another major source of water for California is the nation’s largest fresh-water reservoir, Lake Mead at the southern tip of Nevada. It’s a crucial source, not just for California, but for Nevada, Arizona, other western states, and even Mexico. Unfortunately Lake Mead recently sank to record low levels, meaning that yet another water reservoir for California (and many other areas) is perilously low.
California is one of the most productive agricultural areas in the nation. But the drought has put a huge dent in their agriculture already. If the water situation doesn’t improve things will be even worse, and honestly, there’s not much hope for improvement soon. It underscores the fact that threats to the water supply can also threaten the food supply.
There’s also enhanced risk from wildfire. Numerous studies have shown that the increase in wildfire in the western U.S. is not just some consequence of fire management, as deniers like to claim (if they can’t deny a problem they’re sure to find something else to blame it on). It’s because of climate change. Western states are expecting a very bad wildfire season this year, and for Washington state they’re already off to a horrific start.
I hope the situation improves soon. Even if it does, the recent drought should be taken as a warning that our tampering with the climate has consequences. We all need to prepare for those consequences, in full knowledge that as bad as things can get today (and California is in bad shape), future instances won’t just be a repeat of a dire situation. They’ll be worse.
Unfortunately, if the California drought situation does improve soon, the natural human tendency will be to forget about the danger — “out of sight, out of mind.” The best we can hope for is that California will soon recover and that the last few years’ troubles will be a “word to the wise.”
It’s not that the word isn’t clear enough. Usually, it’s just the fact that we’re not wise enough.