On August 20, the journal Geophysical Research Letters published a study that quantifies the extent that climate change is playing in the Western drought, currently in its fourth year.  According to the research, carbon dioxide emissions from the burning of fossil fuels is responsible for between 8 and 27 percent of the current drought’s severity.  According to a recent report from UC Davis, the economic impact of the drought in 2015 alone is $2.74 billion, an increase of $540 million over 2014 losses. For an in-depth look at how the drought is affecting agriculture in California, check out our recent article on the topic.  

While climate scientists have understood that climate change likely plays a role in worsening drought cycles, previously it was unknown to what extent rising surface temperatures are playing in the current drought’s severity.  Scientists compared the impact of various factors on water evaporation rates, including humidity, wind speed and solar radiation, and temperature.  They found that temperature is the biggest factor in rates of soil moisture, and increasing temperatures mean less water in the soil, which exacerbates drought conditions. 

They also modelled current and expected temperatures to estimate what rate of evaporation will occur in the future – and how big an impact this will play in drought cycles going forward.  With rising temperatures, evaporation rates will continue to increase.  Therefore, even when rain and snowfall is abundant, evaporation rates will be higher than historic averages.  The study finds that temperatures in the state have increased an average of 2.5 degrees Fahrenheit between 1901 and 2014.  On current surface temperature trajectories, by 2060 permanent drought will be the norm in California. 

California Governor Jerry Brown (R) called the study a “wake up” for “Republicans, foot-dragging corporations and other deniers … [to] take sensible action before it’s too late.”  Brown has been criticized in the past for failure to act as quickly as many saw as necessary, to mandate cuts to water use statewide, and for leniency on agricultural producers, compared to urban users. 

Depending on where the influence of climate change actually falls in that estimate of 8 to 27 percent, will translate to how long until climate change becomes the major factor in drought severity in the state.  According to lead study author Dr. A Park Williams of Columbia University’s Lamont-Doherty Earth Observatory, "If it turns out that the real contribution is closer to 8%, it means the global warming process is underway and may take a few more years before it becomes a dominant player in California drought conditions … If, however, it is closer to 27%, it means we have already reached [that] point."

In addition to agricultural production, wildlife is being impacted negatively, as well as rural communities.  UC Davis states that there are currently 2,000 dry wells in rural counties, which haven’t made the infrastructure investments that urban counterparts have. Jeffrey Mount, Senior Fellow at the PPIC Water Policy Center, commented, “California needs a longer-term effort to build drought resilience into the most vulnerable areas.”


For more information see: 

California drought: Climate change plays a role, study says. But how big?, The LA Times 

New paper helps define climate change's contribution to the Calif. drought, E&E News 

Economic Analysis of the 2015 Drought For California Agriculture, UC Davis

Contribution of anthropogenic warming to California drought during 2012–2014, Geophysical Research Letters