HR: 08:00h
AN: H51I-01 INVITED     [Abstracts]
TI: Consensus and Scatter Among Recent Climate-Change Projections for California
AU: * Dettinger, M
EM: mddettin@usgs.gov
AF: U.S. Geological Survey, Scripps Institution of Oceanography UC San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0224 United States
AB: During the past year, numerous climate-change projections have become available from climate-modeling groups around the world, in support of the upcoming Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (AR4). Given the many past efforts to assess potential climate-change effects in California and the western US, using previous projections, a question of great practical importance to local and regional decision makers is: Are the IPCC AR4 projections substantively different from previous projections? An ensemble of 84 projections of climate change for California from 12 different models responding to 3 greenhouse-gas emission scenarios each (with some modeling groups providing multiple climate simulations under the various scenarios) was resampled to estimate joint temperature and precipitation projection distribution functions (pdfs) for selected decades of the 21st Century. The same method was applied to an 18-member projection ensemble (projections by 6 different models under 3 emission scenarios each) from the 3rd IPCC Assessment Report (AR3, 2000) and subsequent activities. Comparisons of the pdfs of California climate change obtained from the AR3 and AR4 projection ensembles show that: (a) The amounts of scatter within the AR3 and AR4 temperature-change ensembles do not noticeably differ from each other, despite the much larger size and scope of the AR4 ensemble; (b) the strong tendency for AR3 precipitation projections to trend little is even stronger in the AR4 ensemble; (c) projected southern Californian precipitation rates also cluster near historical means in both ensembles, although the AR4 ensemble exhibits some drift towards drier conditions; and (d) projected warmings in the AR4 ensemble are about 1° C less than the AR3 projections. Even when the AR3 and AR4 ensembles were culled to include only projections from the same modeling groups/models and very similar emission scenarios, AR4 warming were still (on the whole) about 0.5° C less than their AR3 counterparts. The hydrologic implications of the ensembles' similarities and differences will be explored by comparisons of watershed simulations driven by representative climate-change projections from the AR3 and AR4 pdfs.
DE: 1630 Impacts of global change (1225)
DE: 1637 Regional climate change
DE: 1840 Hydrometeorology
DE: 1860 Streamflow
SC: Hydrology [H]
MN: Fall Meeting 2005