As the world warms, the overall area of North America covered by snow is decreasing. One reason is that an increasing percentage of winter precipitation is falling as rain instead of snow in many locations. A Climate Central report found that between sea level and 5,000 feet in elevation, a smaller percentage of winter precipitation is falling asMore
Winter is the wet season in California, and the amount of rain and snow that has fallen across the Golden State in the past few months has been phenomenal, building up the mountain snowpack that is so crucial to the state’s water supplies.
The much-needed soaking was what was expected last winter, when an exceptionally strong El Niño was in full swing — but despite a few storms, that winter provided little relief for the drought-plagued state. The juxtaposition of the two winters shows that El Niño isn’t everything when it comes to Western winter precipitation.
Almost all of the precipitation that falls in California does so between November and April. In Los Angeles, 91 percent of its annual rain comes during those months. In Sacramento, that number is 88 percent. As a result, the snow that falls in the state’s Sierra Nevada range during the winter helps fuel streams and reservoirs as it melts later in the year, providing water during the dry summer months.
In both Los Angeles and Sacramento, January and February are normally the wettest months of that wet season, and that was certainly the case this year. The numerous storms that crashed into California during the past two months led to Los Angeles having nearly double (181 percent) its normal rain for those two months, and Sacramento with more than double (256 percent) its normal rain. In fact, Sacramento had its wettest January on record, with 9.92 inches of rain.
And the snow in the Sierra is bountiful this year. Through March 10, the snow on the ground was 178 percent of normal for the date, indicating nearly 4 feet of water is locked up in the snowpack.
But it was just over a year ago that one of the strongest El Niños on record was roaring in the Pacific Ocean, and drought-weary Californians hoped it would bring badly needed precipitation during the 2015-16 wet season. While there were some modest benefits, it largely fell flat, and the multi-year drought continued into the summer of 2016.
The wet season has been entirely different this year. The El Niño was long gone by the summer of 2016, yet California just finished its second wettest winter on record. Only 1969 was wetter, and that was not an El Niño year either. Of the three big El Niños of the last generation (1982-83, 1997-98, and 2015-16), only the 1997-98 event gave California one of its 10 wettest winters on record, coming in third.
This year has served as reminder that the seasonal weather depends on many highly variable atmospheric and oceanic patterns, such as the atmospheric rivers that emptied over California this season. El Niño is an important driver of the weather, but is not the only one.
No question that this winter has dramatically improved the California water resources for 2017, but not all parts of the water cycle respond so quickly. It takes much longer for water to percolate through the ground and replenish underground aquifers. That will not happen in one season, as it usually takes multiple years of normal or above-normal rainfall to bring them back toward normal.
California is known for long droughts followed by exceptional wet periods, but the droughts have gotten worse over the last century. As the world warms from climate change, and the long-term temperature climbs, the atmosphere evaporates more water, not just from lakes and oceans, but from soils. So while climate change does not strictly cause droughts, it certainly can make them worse.
And while the population growth in California has recently slowed, it has doubled since 1970, meaning demand for water will continue to grow, and managing water resources will continue to be a challenge. This winter was a welcome relief to the water stresses of the past few years in California, and it shows that El Niño is not a cure-all for California drought.
While there is break for now, California’s long-term water woes are likely to return to the forefront in the decades to come.