Uncertainty Analysis of the Impact of Sea Surface Temperatures on Seasonal Drought over the conterminous US (1901–2012): A Bayesian Approach

In recent decades, the Conterminous US (CONUS) have exposed to flash droughts more often, which initiated suddenly and persisted during one season with a focus on a region, and recovered with a new season. The regional hydroclimate of the CONUS has been changed and thus diverse climate drivers for drought over the CONUS lead to a more complex mechanisms for seasonal drought over a region, especially during summer. The role of SST in the occurrence of seasonal drought is in question for decadal forecasting. We focus on meteorological summer and winter drought defined by the first quantile of precipitation from the Climate Research Unit (CRU, 1901-2010). We compute the probability density function (PDF) for summer and winter drought occurrence over the four regions of the CONUS from the scaled-up and fitted beta distribution. Also, we compute the PDFs given certain phases of PDO, AMO, and ENSO. Observational data suggest that interannual and decadal oscillation over the Pacific and Atlantic play diverse role in seasonal drought occurrences. A warm phase of ENSO and PDO decrease the probability to occur summer drought over the Western US by 10%, however they increase summer drought over the Northern US by 10%. Interestingly, The Eastern US has a less chance to have seasonal drought by more than 10% during a cold phase of PDO and a warm phase of AMO, which are well known as favorable SST condition for continental multi-year CONUS drought. Finally, we speculate that the warming of northern hemisphere SSTs since 1970s can contribute to a delayed response of land surface to true natural variability in terms of drought and pluvial occurrences.