Influence of ENSO on Droughts in the U.S. Southwest and California

Abstract:

The impact of El Niño–Southern Oscillation (ENSO) on precipitation and droughts in the U.S. Southwest and California is assessed based on observational data and coupled global climate model simulations. The co-variability between 67-year (1948–2014) Southwest winter precipitation and Pacific sea surface temperature (SST) is analyzed using the singular value decomposition method. Results indicate strong associations between Southwest drought and La Niña during 1948–1977 and between Southwest pluvial and El Niño during 1978–1999. The relationship between Southwest precipitation and tropical Pacific SST is relatively weak after 1999, particularly for the most recent 3-year drought in California. This is likely related to the weakening of ENSO variability since 2000. A comparison between two 480-year model simulations with and without ENSO variability suggests that ENSO can alter the characteristics of precipitation, and thus droughts over the Southwest and California in terms of frequency and intensity. In the presence of ENSO, the variability of Southwest precipitation is enhanced, and further, shifts toward lower frequencies. The modeling study demonstrates a sensitivity of the Southwest precipitation-related teleconnection to both the phase and intensity of ENSO, which helps understand the observed decadal changes in the strength of the link between Southwest precipitation and ENSO. The atmospheric circulation and hydrological anomalies related to the 2012–2014 California drought are also examined in the context of both the past 67-year observations and the 480-year model simulations.