Assessing the impact of ENSO on drought in the U.S. Southwest with NCEP climate model simulations

- Decadal changes in the relationship between U.S. Southwest precipitation and ENSO.
- ENSO variability shifts Southwest precipitation toward lower frequencies.
- Southwest precipitation-related teleconnection is sensitive to the phase and intensity of ENSO.

SummaryThe impact of El Niño-Southern Oscillation (ENSO) on U.S. Southwest precipitation and drought 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. 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 in terms of frequency and intensity. In the presence of ENSO, the variability of Southwest precipitation is enhanced, and further, shifts toward lower frequencies. In addition, the chance for the ENSO-related precipitation pattern to persist over 3-4 years in the Southwest is higher in the simulation with ENSO than that without ENSO. The modeling study also 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.