One of the most devastating weather disasters in the past decade wasn’t a tornado tearing through the Plains or a hurricane swirling ashore, but rather the slow-motion dehydration of the most populous state in the United States. California has spent the past five years mired in its worst drought in centuries, which devastated crops and water supplies across the state. While the adverse effects of the drought will take much longer to wear off, the state recently got some good news about its improving liquid fortunes.
The latest issue of the United States Drought Monitor (USDM) shows that just over half of California is still in a drought. More than half of an enormous state steeped in drought sounds pretty bad, but conditions have actually improved tremendously over the past couple of months.
The United States Drought Monitor for California on January 31, 2017. Image Credit: Dennis Mersereau
At the end of January 2016, 95 percent of California was in some level of drought, and 40 percent of that area was in that scale-topping "exceptional drought" category. Today, one-fifth of the state is still in a severe drought, and a tiny portion—just under 2 percent—is in an extreme drought. No part of California is experiencing an exceptional drought anymore, the most urgent level on the five-point scale used to determine drought status.
The USDM is a weekly analysis drawn by scientists who look at precipitation, groundwater, and soil data to determine how dry the ground is across the entire country. The lowest categories—abnormally dry and moderate drought—are usually transient and can come and go with unusual dry spells. But in the case of California’s water troubles, extreme and exceptional drought conditions have become commonplace over the past few years.
The worst drought in the modern history of California began at the beginning of 2012 and steadily worsened over the next five years. The intensely dry weather came to a head in 2014, leading some scientists to declare the presence of a “megadrought”—a lack of rain in the western United States so extreme and long-lasting that such conditions haven’t occurred in this region since the 12th century. But then conditions improved somewhat during the winters of 2015 and 2016, culminating with this winter’s drought-busting deluge.
The progression of California’s drought as seen through the USDM’s weekly drought analyses. Image Credit: Dennis Mersereau
The solution to drought is always a prolonged period of steady, soaking rainfall and, in the case of mountainous regions, decent storms with accumulating snow. Weather patterns began to shift early this winter into a configuration that let ample moisture flow over drought-stricken areas of the West Coast. A steady flow of tropical moisture, a phenomenon known as an “atmospheric river,” helped storm systems wring out as much precipitation as possible over areas that needed it the most.
The recent period of much-looked-for rain in California started in earnest around the middle of December 2016 and continued through the end of January. After just above average precipitation in December in San Francisco, the Bay Area saw nearly twice its normal January rainfall by the end of January. It’s a similar story across the rest of California.
Precipitation between November 3, 2016 and February 1, 2017, as compared to normal. Image Credit: Dennis Mersereau
There’s even better news in the mountains, where springtime runoff contributes significantly to reservoirs and groundwater in lower-lying areas of the state. The storms that brought rain to the rest of California brought even greater amounts of snow to the mountains. Some mountainous towns have snow depths taller than most houses. A ski resort near Lake Tahoe saw so much snow in one January snowstorm that their chair lifts were buried.
But the latest forecast from the Climate Prediction Center calls for a general trend of below-average rainfall during the month of February and equal chances for below- or above-average precipitation through the early spring months. It’s worth noting that another long period of dry weather could erase the gains California has seen over the past month or two. More often than not, drought begets drought, and it can be a tough cycle to break once it begins. Still, the recent rainfall is a welcome sign nonetheless, and one that will hopefully continue in rainy seasons to come.