The dramatic switch from extreme drought to severe flooding in California, and the accompanying flip from atmospheric ridge to trough in the northeastern Pacific, exemplifies the pathways to an intensified water cycle under a warming climate.

The prolonged drought in California from 2012 to 2016 was recently broken by a dramatic reversal in the form of extreme precipitation events and flooding. In the Sierra Nevada mountains, precipitation in January and February 2017 exceeded that of the previous wettest year on record, 1982–1983. For the first time in its history, water poured over the emergency spillway of the Lake Oroville dam, California's second largest reservoir. The excessive precipitation and resultant floods led to the declaration of yet another state of emergency, this time from a very different perspective with regard to the 2014 drought. The media, resource management entities, and the scientific community have already started to inquire as to why there was such a sudden switch from extensive drought to the other extreme.

Many studies that were motivated by the unprecedented recent drought have focused on the attribution of a persistent high-pressure ridge stationed off the west coast during the height of the drought^1,2,3. In the winter of 2016–2017, an enhanced low-pressure trough appeared in the same location, initiating and directing sequential atmospheric river events toward California and causing high levels of precipitation. Here, we outline that the dramatic appearance of this enhanced trough in 2016–2017 is 'the other side of the coin'; this flip side was implied and even projected in some previous studies^2,4,5 analysing the high-amplitude, drought-producing ridge. The extreme flooding of the 2016–2017 winter coupled with the preceding severe drought is an exemplification of an intensified water cycle over California.