PLEA Network

14 February 2017, Think Progress, Sinking from drought, California is now also flooding. After weeks of rain, Northern California’s surface water systems have been pushed to the breaking point, even while the effects of a five-year drought continue to threaten the state’s long-term groundwater supplies. More than 180,000 people were evacuated Sunday afternoon after spillways for the Oroville Dam in Northern California showed signs of possible collapse. The potential flooding comes as California begins to emerge from its historic, drought. But despite the overabundance of water on the surface, drought conditions underground have likely had a permanent impact on the state. Even under the best conditions, it could take half a century for underground reservoirs to refill. Recent analysis from the California Institute of Technology shows that drought — combined with water use — has caused parts of California to sink, perhaps permanently. Some places show up to two feet of subsidence over the past two years. That’s because as surface water from rain and snowmelt has decreased, farmers have been using more groundwater from reservoirs. “Subsidence caused by groundwater pumping in the Central Valley has been a problem for decades,” write the authors of a new study, which uses NASA data to track California’s sinking. Pumping groundwater reduces the support below-ground aquifers give to the surface, causing it to sink. In recent years, that process has been sped up, as California’s drought has reduced the surface water available to farmers. While surface water can come in the form of rain, or snowmelt, groundwater sits in aquifers and is the result of a slow build up of water below ground. Read More here