Californian drought: The processes and factors controlling the 2011-2016 drought and winter precipitation in California

Abstract: The factors and processes controlling winter precipitation in California and the 2011-2016 California drought have been examined in a literature study. The study showed that mid-latitude cyclones are the systems that generate winter precipitation in California. The location of high- and low-pressure systems in the northeast Pacific Ocean have a huge impact on the winter precipitation as they largely determine the direction of the jet stream, which transports the moisture-holding cyclones in over the North American west coast. Baroclinic instability and warm sea surface temperatures determines the intensity of cyclones. Orographic precipitation in mountainous regions is a significant mesoscale process, through which snowpack accumulates. Furthermore, the phases of the El Niño-Southern Oscillation and the Pacific decadal oscillation generally affects Californian winter precipitation to a degree. The El Niño-Southern Oscillation probably affected the drought, but the Pacific decadal oscillation influence on the drought is unclear. Global warming and climate change surely influence the aridity in California, but the drought was probably mainly caused by natural variability.