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Wildfire Risk in a Changing Climate
Taylor, Steve W.
The purpose of this project is to increase the ability to forecast impacts of climate change on wildfire activity in British Columbia, which was identified is a key uncertainty in a review of climate change impacts on forest management (BCMOFR 2006). Through their impact on forest age structure and species composition, forest fires can impact the sustainability of timber supply and other resource values (Armstrong 1999). Average global temperature increases are expected to increase between 1.3 and 1.7 degree by 2050 over 19xx-19xx levels (Field et al 2007), although there will be regional variation in temperature and precipitation changes, with higher temperature increases in northern regions). Flannigan et al (2002) predicted an increase in seasonal fire severity rating and an increase in fire season length of 2-3 weeks in BC by the year 2085. Recent work by Flannigan et al (2005) suggested a 74-118% increase in average area burned in Canada by the end of this century (3xCO2 scenario) without taking into account changes in vegetation, ignitions, fire season length and human activity. While weather is a strong driver, as area burned increases, there may be negative feedback due to an increase in the proportion of less flammable vegetation in the landscape. However, results for BC were less conclusive. Further work is needed to improve predictions of impacts in BC to guide mitigation strategies. Between 1919-2007 approximately 20 million ha were burned in BC (Fig1). However, the annual area burned in BC, as elsewhere, is highly variable, and follows a negative exponential distribution (Fig 2). This variation, which is mainly due to weather, and the frequency of extreme years, has a great influence on timber supply and other resource values. The amount of winter precipitation determines whether forest fuels are saturated, while the amount of snow and timing of the spring melt influences the length of the fire season. Westerlink et al (2006) found correlations between forest fires and spring snowmelt timing, which they also linked to summer drought conditions at mid-elevation locations in the western USA. During the fire season, the flammability of forest fuels depends on the frequency, duration and intensity of drying periods and precipitation events; with large forest fires being associated with atmospheric circulation patterns characterized by a prominent ridge with a strong meridional flow (Skinner et al. 2002; Fauria and Johnston 2006). Stahl et al (2006) classified synoptic circulation patterns over BC into 13 types (Fig 3) and examined their frequency in relation to the El Nino Southern Oscillation and Pacific Decadal Oscillation (PDO). Positive PDO was associated with warm dry winters in mainland BC. Forest fires are mostly associated with synoptic types 1 and 2 (Fig 4), however these are also the dominant types in summer. More work is needed to examine the effect of these circulation types on fire weather and climate factors. An understanding of the effects of the various modes of variability on local climate is important to effective downscaling of GCMs (Stahl et al 2006). However, little work has been done to examine potential effects of climate change on the frequency distribution of area burned. This project with address three key research questions: 1. How may predicted changes in temperature and other weather variables due to global climate change and large scale circulation patters affect future fire weather? 2. How will changes in fire weather impact changes in fire risk, including the probability of extreme fire years? Are there potential feedbacks? 3. How will changes in area burned distribution impact sustainability of forest resources? Realizations of future fire weather will be developed from a) an ensemble of GCM model output and b) from stochastic weather simulation from monthly weather normals, adjusted for predicted future anomalies (Regniere and St. Amand 2006). The simula ...
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Executive Summary
Poster: Prediction of future lightning frequency in British Columbia
Poster: Stochastic simulation of seasonal fire danger from monthly climate normals - an Early Warning application
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