HR: 17:15h
AN: B54A-05    [Abstracts]
TI: Reevaluation of the spring onset/fire association in the western U.S. using Phenological vs. Hydrological Models
AU: * Westerling, A L
EM: awesterling@ucmerced.edu
AF: Sierra Nevada Research Institute, UC Merced, P.O. Box 2039, Merced, CA 95344, United States
AU: Betancourt, J L
EM: jlbetanc@usgs.gov
AF: USGS Desert Laboratory, 1675 W. Anklam Road, Tucson, AZ 85745, United States
AU: Schwartz, M D
EM: mds@uwm.edu
AF: Department of Geography, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201-0413, United States
AB: An important aspect of climate variability and change is the exact timing of the transition from winter to spring, generally defined here as spring onset. Spring onset can have important hydrological and ecological consequences, including changes in the timing of snowmelt and snowmelt runoff, in timing of plant and animal phenologies and their interactions, in ecosystem fluxes, and in the probabilities of ecological disturbances such as fire and insect outbreaks. Spring onset can be variably defined, which can affect its use as a predictor. To evaluate changing fire probabilities in the western U.S., Westerling et al. (2006) used center of mass of annual streamflow (CT, after Stewart et al 2005) for snowmelt-dominated gauge records as a proxy for spring onset, and compared it with the number of forest wildfires greater than 400 ha annually around the western U.S. This study indicated a strong association between large wildfire occurrence across the West and CT, and a particular sensitivity to the timing of snowmelt in the Northern Rockies. Though the timing of snowmelt can affect fire occurrence in several ways, the use of CT as a proxy for spring onset biased the analysis towards higher elevations and latitudes. To skirt this bias, we undertook a similar analysis using Spring Indices (SI) developed from cloned lilac and honeysuckle phenological data and representing seasonally integrated changes in temperature (Schwartz et al. 2006). The SI models can be generated at any location that has daily maximum–minimum temperature time series, and allowed comparison of large fire occurrence in defined regions with a network of select weather stations across the West for which we computed SI. The SI/fire comparison showed strong associations between SI at weather stations, particularly those in the Central Rockies/Colorado Plateau and large fire frequency in the northern, central and southern Rockies, as well as in the Sierra Nevada, but less so in southern California and the Black Hills. Given large differences in fire seasonality, vegetation type, and the importance of snowpack, explanations for the spring onset/fire association could be inherently complex. Though they also have biases and shortcomings, phenological models such as SI may be particularly useful in predicting climate change impacts on fire and other phenomena, and could offer more precision and better lead time in fire forecasting. Schwartz, M.D., R. Ahas, A. Aasa 2006: "Onset of spring starting earlier across the Northern Hemisphere" Global Change Biology, 12: 343-351. Stewart, I.T., D.R. Cayan and M.D. Dettinger, 2005: Changes toward earlier streamflow timing across Western North America. Journal of Climate, 18, 1136-1155. Westerling, A.L., H.G. Hidalgo, D.R. Cayan, T.W. Swetnam 2006: "Warming and Earlier Spring Increases Western U.S. Forest Wildfire Activity" Science, 313: 940-943.
UR: http://tenaya.ucsd.edu/~westerli/
DE: 0400 BIOGEOSCIENCES
DE: 0468 Natural hazards
DE: 0476 Plant ecology (1851)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1630 Impacts of global change (1225)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting