An extreme future for California

California is projected to swing from drought to extreme rainfall and flooding more often in the future, reports a study published online this week in Nature Climate Change. These results highlight the continuing challenge faced by the water infrastructure in the most populated state in the United States.

California has recently undergone a rapid hydrological change and its worst drought in recorded history plagued the entire state from 2010-2016. In the winter of 2016-2017, however, California was inundated by heavy rainfall and flooding - culminating in the Oroville Dam disaster that forced 250,000 residents to evacuate.

Daniel Swain and colleagues model how the frequency of these rapid, year-to-year transitions from extreme dry to wet conditions - which they dub ‘precipitation whiplash events’ may change in California’s future as a consequence of man-made warming. The authors predict a 25% rise in the frequency of precipitation whiplash events by the end of the twenty-first century in northern California, increasing up to 100% in southern California. These changes occur primarily due to an increase in wet extremes, which amplify the already variable precipitation across the region. This intensification of the water cycle will increase the pressure on California’s infrastructure to both alleviate water shortages during droughts and prevent flooding during heavy rain.