Research on tree rings shows the current California decade is beyond severe.
The current event is the most severe drought in the last 1200 years, with single year (2014) and accumulated moisture deficits worse than any previous continuous span of dry years.
The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.
Groundwater pumping in California has increased, with many new wells being drilled. This creates problems like subsidence, as well as draining the aquifers.
Mary Scruggs [ Supervising Engineering Geologist, Department of Water Resources] began by summarizing the importance of groundwater. “Groundwater is critical to California,” she said. “It provides up to 40% during normal years; during dry years, it can provide a lot more. There’s been a lot of pressure on groundwater over the last few years. With the dry years and the extreme drought, some areas are using a lot more groundwater then they have. The drought, and pumping of the groundwater also can create problems in some of the areas, including subsidence, saline intrusion, movement of contamination, and there’s also impacts on some of the agricultural areas because some of the areas have been fallowed.”