HR: 14:00h
AN: B33F-02    [Abstracts]
TI: A Regional Climate Modeling Study of the Effects of Irrigation and Urbanization on California Climate
AU: * Kueppers, L M
EM: kueppers@pmc.ucsc.edu
AF: Department of Earth Sciences University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Snyder, M A
EM: msnyder@pmc.ucsc.edu
AF: Department of Earth Sciences University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Sloan, L C
EM: lcsloan@pmc.ucsc.edu
AF: Department of Earth Sciences University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Bryant, S
EM: sbryant@pmc.ucsc.edu
AF: Department of Earth Sciences University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AB: California and neighboring states have seen significant changes in land cover and land use over the past century, with expanding urbanization along the Pacific coast and extensive agricultural development inland. Expanded irrigation and urbanization both have implications for local and regional climate due to changes in land surface albedo, vegetation roughness, maximum vegetation cover, and seasonal variation in soil moisture. We modified a regional climate model, RegCM3, which already included irrigated and dryland crop types, to include urban and suburban land cover types. We used the model to quantify the difference in climate between cases using pre-settlement land cover and modern (~1990) land cover. We used 1979-1989 NCEP reanalysis data as input at the model perimeter, encompassing a very wet year and several very dry years. We analyzed the final 8 years of output to give soil moisture adequate time to equilibrate. Irrigated agricultural land in California's Central and Imperial Valleys had the strongest effect on both temperature and relative humidity. During the April-November dry season, monthly average surface temperature was cooler after conversion from pre-settlement vegetation to modern irrigated cropland. During the same period, relative humidity was higher. We found no change in precipitation rates. The effects were likely due to the increased soil water availability with irrigation, as the changes largely vanish during the rainy months of December-March. At the resolution of our model (30km), we found no significant effects of urbanization on local or regional climate. This could be due to the proximity of most urban areas to the coast, or due to the urban parameterization that we employed. Overall, the modeled effect of irrigation on temperature is comparable in magnitude, but opposite in sign, to the temperature effect of business-as-usual CO2 increases predicted for California by RegCM. This result emphasizes the need for models of future regional climate change to incorporate forecasts of regional land use change.
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1632 Land cover change
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3355 Regional modeling
SC: Biogeosciences [B]
MN: Fall Meeting 2005