21st Conference on Climate Variability and Change


Sensitivity of the mid-21st century cold season hydroclimate in California to global warming: An RCM projection based on NCAR CCSM3 projection and SRES-A1B emission scenarios

Jinwon Kim, Univ. of California, Los Angeles, CA; and Y. Chao, A. Eldering, R. Fovell, A. Hall, Q. Li, K. N. Liou, J. C. McWilliams, D. E. Waliser, and S. Kapnick

A projection of the cold season cold season surface hydroclimate in the California region during the mid-21st century has been made using the dynamical downscaling method in which a global climate projection generated by NCAR CCSM-3 is downscaled using a regional climate model (RCM), the Weather Research and Forecast (WRF) model. The CCSM3 global climate projection is based on the SRES-A1B emission profile. The cold season covers the 6-month period, October-March, which includes fall (October-December: OND) and winter (January-March: JFM). The regional climate change signals are calculated as the differences between the RCM climatology for the two 20-year periods that represent the late 20th century (1961-1980) and the mid-21st century (2035-2054). The results show that the low-level temperature in California will increase by 1-2.5K with larger increases in high elevation regions and in winter. Noticeable decreases in snowfall, snow-water equivalent (SWE), and surface albedo in high elevation regions in the projected mid-21st century climate suggest that the temperature increases in the high elevation regions are partially amplified by local feedback through snow and surface albedo. Precipitation decreases over the entire cold season but shows well defined interseasonal variations; a pattern of positive (negative) signals in the northern (southern) California region during fall is reversed in winter. The seasonal variations in the precipitation change pattern are mainly associated with the climate change signals in rainfall. Snowfall decreases in the warmer climate, most noticeably in winter. The changes in seasonal precipitation result in the reduction in snowmelt, seasonal-mean SWE, and runoff during the cold season, especially in high elevation regions. The decrease in the high elevation snowpack is of a special concern as it is among the main sources of warm season water supply in California.

Poster Session 7, Regional climate modeling
Thursday, 15 January 2009, 9:45 AM-11:00 AM, Hall 5

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