DroughtsWarming temperatures cause of recent California droughts
California has experienced more frequent drought years in the last two decades than it has in the past several centuries. That observed uptick is primarily the result of rising temperatures in the region, which have climbed to record highs as a result of climate change, Stanford scientists say. Researchers have examined the role that temperature has played in California droughts over the past 120 years. They also examined the effect that human emissions of carbon dioxide and other greenhouse gases are having on temperature and precipitation, focusing on the influence of global warming upon California’s past, present, and future drought risk. The team found that the worst droughts in California have historically occurred when conditions were both dry and warm, and that global warming is increasing the probability that dry and warm years will coincide. The findings suggest that California could be entering an era when nearly every year that has low precipitation also has temperatures similar to or higher than 2013-14, when the statewide average annual temperature was the warmest on record.
California has experienced more frequent drought years in the last two decades than it has in the past several centuries. That observed uptick is primarily the result of rising temperatures in the region, which have climbed to record highs as a result of climate change, Stanford scientists say.
In a new study, published in the 2 March issue of the journal of the Proceedings of the National Academy of Sciences, researchers led by Stanford professor Noah Diffenbaugh, examined the role that temperature has played in California droughts over the past 120 years. They also examined the effect that human emissions of carbon dioxide and other greenhouse gases are having on temperature and precipitation, focusing on the influence of global warming upon California’s past, present, and future drought risk.
A Stanford University release reports that the team found that the worst droughts in California have historically occurred when conditions were both dry and warm, and that global warming is increasing the probability that dry and warm years will coincide. The findings suggest that California could be entering an era when nearly every year that has low precipitation also has temperatures similar to or higher than 2013-2014, when the statewide average annual temperature was the warmest on record.
“Of course low precipitation is a prerequisite for drought, but less rain and snowfall alone don’t ensure a drought will happen. It really matters if the lack of precipitation happens during a warm or cool year,” Diffenbaugh said. “We’ve seen the effects of record heat on snow and soil moisture this year in California, and we know from this new research that climate change is increasing the probability of those warm and dry conditions occurring together.”
Diffenbaugh and his team reached their conclusions by analyzing historical observations and computer climate change simulations. They took advantage of a recently released trove of monthly precipitation, temperature, and drought data for California that stretches back to 1895. Using this 120-year observed dataset, the scientists calculated the probability of drought years occurring in different temperature and precipitation conditions.
Their analysis revealed that the years that were both warm and dry were about twice as likely to produce a severe drought as years that were cool and dry. The scientists were also surprised to find that during the early and mid-twentieth century, temperature and precipitation were largely “uncoupled” — that is, they occurred more or less independently of one another.
