Jan 30, 2015

Anthropogenic warming has increased drought risk in California

by
Noah S. Diffenbaugh, Daniel L. Swain, and Danielle Toum
,
Proceedings of the National Academy of Sciences
  • States that the California drought began in 2012 and now includes the lowest calendar-year and 12-mo precipitation, the highest annual temperature, and the most extreme drought indicators on record
  • Summarizes that extremely warm and dry conditions have led to acute water shortages, groundwater overdraft, critically low streamflow, and enhanced wildfire risk
  • Analyzes historical climate observations from California and finds that precipitation deficits in California were more than twice as likely to yield drought years if they occurred when conditions were warm
  • Finds that although there has not been a substantial change in the probability of either negative or moderately negative precipitation anomalies in recent decades, the occurrence of drought years has been greater in the past two decades than in the preceding century
  • Finds the probability that precipitation deficits co-occur with warm conditions and the probability that precipitation deficits produce drought have both increased
  • Reveals using climate model experiments with and without anthropogenic forcings that human activities have increased the probability that dry precipitation years are also warm
  • Reveals using a large ensemble of climate model realizations that additional global warming over the next few decades is very likely to create approximately 100% probability that any annual-scale dry period is also extremely warm
  • Concludes that anthropogenic warming is increasing the probability of co-occurring warm–dry conditions like those that have created the acute human and ecosystem impacts associated with the “exceptional” 2012–2014 drought in California