Changes in drought risk over the contiguous United States (1901-2012): The influence of the Pacific and Atlantic Oceans

We assess uncertainties in the influence of sea surface temperatures on annual meteorological droughts over the contiguous U.S. within a Bayesian approach. Observational data for 1901-2012 indicate that a negative phase of the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO) elevated annual drought risk over the southern U.S., such that the 4 year return period event becomes a 3 year event, while a positive phase of the Atlantic Multidecadal Oscillation has a weak influence. In recent decades, the impacts of the negative phases of the PDO and ENSO on U.S. drought have weakened and shifted toward the southwestern U.S. These changes indicate an increasing of role of atmospheric variability on the U.S. drought overall with implications for long-term changes in drought and the potential for seasonal forecasting.