Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Relationship between decadal precipitation anomalies in the Southwestern U.S. and global SSTs: Insights from the IPCC multi-model ensemble

Antonietta Capotondi

A subset of the climate model simulations performed in support of the Intergovermental Panel for climate change (IPCC) Assessment Report 4 (AR4) has been analyzed to examine the relationship between the evolution of precipitation in the Southwestern US (SW) at decadal timescales and global sea surface temperature (SST) conditions. Previous studies, primarily based on observations and atmospheric model sensitivity experiments, have related precipitation deficit and drought conditions in the SW (i.e. the Dust Bowl in the 1930s) to cold tropical Pacific SSTs similar to those observed during La Niña events, while the influence of SST anomalies in other ocean basins is more uncertain. The large IPCC archive, including simulations of pre-industrial, present-day, and future climate scenarios offers a fantastic opportunity to revisit the relationship between SST anomalies in different ocean basins and precipitation anomalies in the SW across a multi-model ensemble. Long (300-500yrs) pre-industrial control simulations are used in this study to more easily isolate natural variability from trends related to anthropogenic factors, and to increase the statistical significance of the results. The model global patterns of SST and hydroclimate over the continents during long periods of precipitation deficit in the SW is consistent with evidence from the relatively-short and sparse observational record, and with paleoclimate reconstructions of past droughts. Correlations between decadal precipitation variations in the SW and global SSTs show a consistent pattern of significant correlations in the Pacific Ocean, which is similar to the observed pattern of Pacific decadal variability. In some models, the P-SST correlation pattern is very similar to the leading EOF of decadal SST, while in other models the leading mode of decadal SST anomalies has its dominant centers of action in the North Pacific, and significant loading in the tropical Pacific is found in the second and higher EOFs.