Neil Berg, Alex Hall, Fengpeng Sun, Scott Capps, Daniel Walton, Baird Langenbrunner, J. D. Neelin
J. Cliamte, submitted. Paper (21MB!)
Abstract A new hybrid statistical-dynamical downscaling technique is described to project mid- and end of-21st century local precipitation changes associated with 36 global climate models (GCMs) in phase 5 of the Coupled Model Intercomparison Project archive over the greater Los Angeles region. Land-averaged precipitation changes, ensemble-mean changes, and the spread of those changes for both time slices are presented. It is demonstrated that the results are similar to what would be produced if expensive dynamical downscaling techniques were instead applied to all GCMs. Changes in land-averaged ensemble-mean precipitation are near zero for both time slices, reflecting the region's typical position in the models at the node of oppositely-signed large-scale precipitation changes. For both time slices, the inter-model spread of changes is only about 0.2- 0.4 times as large as natural interannual variability in the baseline period. A caveat to these conclusions is that interannual variability in the tropical Pacific is generally regarded as a weakness of the GCMs. As a result, there is some chance the GCM responses in the tropical Pacific to a changing climate and associated impacts on Southern California precipitation are not credible. It is subjectively judged that this GCM weakness increases the uncertainty of regional precipitation change, perhaps by as much as 25%. Thus it cannot be excluded that the possibility that significant regional adaptation challenges related to either a precipitation increase or decrease would arise. However, the most likely outcome is no change in local mean precipitation.
Citation Berg, N., A. Hall, F. Sun, S. Capps, D. Walton, B. Langenbrunner and J. D. Neelin, 2014: Twenty first Century Precipitation Changes over the Los Angeles Region. J. Clim., submitted.