The NOAA study says a high-pressure atmospheric ridge off the West Coast blocked important winter storms from California for three winters. Ocean surface temperature patterns made the ridge much more likely.
The decreased precipitation is almost the opposite of what climate change models project. Precipitation is actually projected to increase due to human-induced climate change over most of the state. But warmer temperatures could offset any rainfall increase because of evaporation.
The study was not published in a peer-reviewed scientific journal. And the report’s author says more research on temperature is needed to fully understand California’s drought.