The state of California has experienced the worst meteorological drought in its historical record during 2012-2015. The adverse effects of this multi-year event have been far from uniformly distributed across the region, ranging from remarkably mild in most of California's densely-populated coastal cities to very severe in more rural, agricultural, and wildfire-prone regions. This duality of impacts has created a tale of two very different California droughts—highlighting enhanced susceptibility to climate stresses at the environmental and socioeconomic margins of California. From a geophysical perspective, the persistence of related atmospheric anomalies have raised a number of questions regarding the drought's origins—including the role of anthropogenic climate change. Recent investigations underscore the importance of understanding the underlying physical causes of extremes in the climate system, and the present California drought represents an excellent case study for such endeavors. Meanwhile, a powerful El Niño event in the Pacific Ocean offers the simultaneous prospect of partial drought relief but also an increased risk of flooding during the 2015-2016 winter—a situation illustrative of the complex hydroclimatic risks California and other regions are likely to face in a warming world.

This collection brings together papers published in Geophysical Research Letters on the 2012-2015 California drought.