Too Much of a Good Thing: Flooding Submerges California’s Drought

Date Posted: March 15, 2017

After a lengthy period withering in extreme drought, California’s fortunes have reversed and the state has endured exceptional rain-and-snowfall over the past few months. Creeks, rivers, lakes, and reservoirs that were once far below normal levels are now overflowing from the onslaught of incoming water. As the abundant rain has continued to fall through the winter, employees at the 10 NWS Weather Forecast Offices and River Forecast Center that serve the state have worked tirelessly to prepare and assist local and state officials in their efforts to mitigate, and recover from, the flooding impacts due to the heavy precipitation.

California Drought status as of March 1, 2016 compared to February 28, 2017California Drought status as of March 1, 2016 compared to February 28, 2017

A year ago, nearly 95 percent of California was in some type of drought condition; more than 60 percent of the state was experiencing “Extreme” or “Exceptional” drought. As of February 28, however, only 25 percent remains in any sort of drought, and for the first time since 2013, there is no extreme level drought in California. The remarkable improvement has been due to strong Pacific storm systems that have repeatedly battered the West Coast. Many of these storms are known as “atmospheric rivers” that bring moisture up from the tropics, near Hawaii, all the way into the West Coast. Each of these storms can bring several inches of rain to the CA coast and central valley as well as several feet of snow to the Sierra Nevada Mountains. In these mountains, the snowpack is currently almost double the annual average, and many locations are on pace for their wettest year on record. Not only have these storms nearly erased much of the remaining drought in California, the relentless rain and snow has introduced flooding issues to many areas of the state. Mudslides and debris flows have crashed down the hillsides as heavy rains have fallen, causing flash floods to surge out of previously dry creek beds. As the precipitation has continued throughout the winter, larger-scale river and stream flooding has added to the flash flood danger as rivers and reservoirs rose in response to the repeated rounds of heavy rainfall.

Even normally arid portions of Southern California have not been spared, with 3 significant heavy rainfall events of their own. The most recent event, beginning February 27, had significant impacts for the metro region of San Diego. Widespread rainfall of 2.5 to 5 inches fell onto the region already saturated from the 2 previous events, with a maximum of 9 inches falling on Palomar Mountain, northeast of the city. The resultant flooding put City of San Diego Fire and Rescue swiftwater rescue teams to work. 65 rescues were conducted, including support from US Coast Guard air crews.

Near deadly but successful swiftwater rescue on the San Diego River overtopping the San Diego Mission Road during the night of February 27. Photo: Alex Tardy

Near deadly but successful swiftwater rescue on the San Diego River overtopping the San Diego Mission Road during the night of February 27. Photo: Alex Tardy  

Through it all, NWS employees have been at the forefront of the action, providing Impact-based Decision Support Services (IDSS) to emergency officials. When the first winter storms came ashore beginning in late November, forecasters were ready, providing officials with advance notice in briefings. Officials initially focused on areas of recent wildfire activities where the likelihood of flash flooding and debris flows would be increased. As the relentless rains continued, the NWS progressively enhanced its efforts to provide needed guidance and support to emergency officials. Staffing levels were increased, “round-the-clock” operations began at the California-Nevada River Forecast Center, and briefings were expanded from local to state, regional, and even national level agencies as the scope of the flooding concerns grew. These briefings were vital to emergency operations. Information provided by the NWS helped these officials stage relief crews and swift-water rescue teams in advance of the threat. The offices also deployed hydrologists to better assist officials at the California State Flood Operations Center. Not only have the efforts of the NWS grown in response to the threat, our vital partnerships and collaboration with other agencies have been vital to the success of emergency operations. Officials from NOAA, NASA, the United States Geological Survey (USGS), FEMA, and the US Army Corps of Engineers (USACE) have all played major roles in decision support and ensuring the protection of life and property during periods of significant flooding.

State Flood Officials Meeting at the NWS Forecast Office in Sacramento

State Flood Officials Meeting at the NWS Forecast Office in Sacramento

The severity of this situation of extremes came to a head in mid-February at the Oroville Dam, northeast of Sacramento, where for the first time ever, an auxiliary spillway was utilized due to extensive erosion damage to the main spillway. The torrent of water that overflowed onto the auxiliary spillway then caused more erosion, and officials were forced to evacuate over 200,000 people downstream as the auxiliary spillway’s structural integrity was threatened. The local NWS office in Sacramento sprang into action here as well, deploying an Incident Meteorologist (IMET) to provide onsite weather support for the team responsible for getting the spillway incident under control. The IMET provided critical information to support the efforts aimed at reducing the level of the reservoir so that further runoff was able to be contained utilizing only the damaged primary spillway.

Image from NWS Sacramento outlining danger at Oroville Dam 

Image from NWS Sacramento outlining danger at Oroville Dam 

Nature has graciously given the area a brief respite from the active storms in late February, but the threat remains. Thousands of people had been forced to evacuate in the San Jose area as floodwaters from a more recent storm have inundated the area and storms across extreme southern California have brought the flooding concern further south, in areas previously spared near San Diego. Officials continue to be on high alert, monitoring dams and levees that are being put to the test, holding back more water than they’ve seen in decades. NWS forecasters remain vigilant, continuing to provide precise and accurate information to the emergency management community and protecting the lives and properties of Californians.