Twenty-first century climate model precipitation projections and uncertainty patterns for the California region
Tuesday, April 21, 2015
Baird Langenbrunner1, J David Neelin1, Bruce T Anderson2, Neil Berg1, Alexander D Hall1 and Benjamin R Lintner3, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)Boston University, Boston, MA, United States, (3)Rutgers University New Brunswick, New Brunswick, NJ, United States
Abstract:
Concern has been raised about whether the current California drought heralds a longer-term trend for the state. In global climate models (GCMs) run as part of the Climate Model Intercomparison Project phase 5 (CMIP5), California tends to lie between regions of precipitation increase to the north and decrease in the subtropics. For regional-scale measures of precipitation change, however, the CMIP5 ensemble shows on average a slight increase in wintertime precipitation at the end of the twenty-first century. This increase appears to be associated with an eastward extension of the midlatitude Pacific eddy-driven jet, acting to steer more storms onto the central-to-northern California coast in global warming scenarios. CMIP5 models show marked disagreement in the regional characteristics of these precipitation changes across California, and it is important to understand why individual model responses can vary so widely. The leading spatial patterns of these precipitation change uncertainties are examined. Associated uncertainties in large-scale circulation and temperature fields reveal dynamics at the large scale that feed into regional precipitation change disagreement over California, especially in relation to zonal and meridional shifts in the Pacific jet and wintertime storm track approaching the California coast. Placing twenty-first century precipitation projections into the context of uncertainties inherent in GCMs will help inform discussion of expected change in California and the role that precipitation change can play in a given definition of drought.
