Folsom Lake Reservoir, located at the base of the Sierra foothills in Northern California's Placer, El Dorado, and Sacramento Counties. Credit: USGS

Here in California, drought is on our minds. Now in its fifth year, the drought has broken – and in some cases re-broken – many historical records, including the most severe values of NOAA’s National Climatic Data Center drought indicators, the lowest calendar-year precipitation, the lowest 12-month precipitation, the warmest calendar-year temperatures, the warmest winter temperatures, the lowest April 1st snowpack, and the warmest/driest 3-year period. It has also taken a heavy toll on people and ecosystems, with wells running dry, farmers abandoning crops, wildfires raging, millions of trees dying, and fish species being pushed to the brink of extinction.

Given these impacts, the drought has been the subject of intense public attention, and an explosion of scientific research. At Geophysical Research Letters, we have just released a Special Collection of papers  examining different aspects of the drought, including the large-scale climate context, the long-term paleoclimate context, and the role of anthropogenic global warming. As these papers make clear, the drought is a rare event resulting from a complex set of causes, the confluence of which has been made more likely by anthropogenic global warming.

The most likely outcome is that Californians will face wet conditions over the coming months, and that we will still be facing depleted groundwater, subsidence of aquifers, stressed ecosystems, and wildfire risk after this El Niño passes.

The GRL special collection also includes a Commentary by Daniel Swain, a Ph.D. student at Stanford University. Although as his Ph.D. advisor I am a biased observer, it is fair to say that through his scientific research, his widely-followed California Weather Blog, and his weekly media requests, Daniel is one of the leading authorities on California’s weather and climate. The abstract of Daniel’s Commentary provides an incisive summary of the drought, and of the GRL Special Collection.

As Daniel’s summary indicates, the current El Niño conditions are providing hope that the drought will break. But, as Chris Field and I have written elsewhere, and as Daniel and others have also articulated, it would take a monumentally wet winter to enable recovery from the drought. And should that much water fall from the sky in a single season, our water system will be hard-pressed to store it all. So, while there is uncertainty in exactly what will unfold, the most likely outcome is that Californians will face wet conditions over the coming months (including heightened risks of flooding and mudslides), and that we will still be facing depleted groundwater, subsidence of aquifers, stressed ecosystems, and wildfire risk after this El Niño passes. And given the reality of global warming, we are likely to continue to face growing risks of these conditions – extremely warm and dry, punctuated by extremely wet – in the future.

To their credit, decision makers across many levels of local, state and federal government have heard this message. Indeed, in my experience, this drought has provided a shining example of decision makers seeking – and trusting – scientific input. This drought is a tremendously complex event. Understanding that complexity has required sustained effort by a number of research groups, with insights being shared in the peer-review literature and an array of public venues. Decision makers and citizens have thus watched the scientific process unfold in real time. And they have integrated the results into decisions in real time. From the new sustainable groundwater legislation, to the drought response led by Gov. Brown, to current consideration of how to manage California’s water resources in the present and future, decision makers have relied on scientists, engineers, economists and legal scholars for insight.

To be sure, those insights have not been the sole source of any decision, and experts have certainly faced piercing inquiry to justify their conclusions. However, I can say from first-hand experience that our leaders in California have treated scientists and other experts with the utmost respect, and have relied on us as trusted sources of objective information. Securing California’s water resources now and for the future is a big challenge, but the fact that our scholarly community is being trusted to play such an important role can give us all confidence that our leaders are building their decisions on a foundation of the best information available.

—Noah Diffenbaugh, Editor-in-Chief, Geophysical Research Letters; email:


Diffenbaugh, N. (2015), Insights into the ongoing California drought, Eos, 96, Published on 25 November 2015.

Text © 2015. The authors. CC BY-NC-ND 3.0
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