Williams, A. Park, Seager, Richard, Abatzoglou, John T., Cook, Benjamin I., Smerdon, Jason E., Cook, Edward R.

Geophysical Research Letters

Published date August 28, 2015

Contribution of anthropogenic warming to California drought during 2012–2014

  • Uses a suite of climate data sets and multiple representations of atmospheric moisture demand to calculate many estimates of the self-calibrated Palmer Drought Severity Index, a proxy for near-surface soil moisture, across California from 1901 to 2014 at high spatial resolution
  • Finds—based on the ensemble of calculations—that California drought conditions were record breaking in 2014, but probably not record breaking in 2012–2014, contrary to prior findings
  • Finds that regionally, the 2012–2014 drought was record breaking in the agriculturally important southern Central Valley and highly populated coastal areas
  • Examines contributions of individual climate variables to recent drought, including the temperature component associated with anthropogenic warming
  • Finds that precipitation is the primary driver of drought variability but anthropogenic warming is estimated to have accounted for 8–27% of the observed drought anomaly in 2012–2014 and 5–18% in 2014
  • Results indicate that although natural variability dominates, anthropogenic warming has substantially increased the overall likelihood of extreme California droughts