Multi-scale influence of vapor pressure deficit on fire ignition and spread in boreal forest ecosystems

[摘要] Climate-driven changes in the fire regime within boreal forest ecosystemsare likely to have important effects on carbon cycling and speciescomposition. In the context of improving fire management options anddeveloping more realistic scenarios of future change, it is important tounderstand how meteorology regulates different aspects of fire dynamics,including ignition, daily fire spread, and cumulative annual burned area.Here we combined Moderate-Resolution Imaging Spectroradiometer (MODIS) active fires (MCD14ML), MODIS imagery (MOD13A1) andancillary historic fire perimeter information to produce a data set of dailyfire spread maps for Alaska during 2002–2011. This approach provided aspatial and temporally continuous representation of fire progression and aprecise identification of ignition and extinction locations and dates foreach wildfire. The fire-spread maps were analyzed with daily vaporpressure deficit (VPD) observations from the North American RegionalReanalysis (NARR) and lightning strikes from the Alaska Lightning DetectionNetwork (ALDN). We found a significant relationship between daily VPD andlikelihood that a lightning strike would develop into a fire ignition. Inthe first week after ignition, above average VPD increased the probabilitythat fires would grow to large or very large sizes. Strong relationshipsalso were identified between VPD and burned area at several levels oftemporal and spatial aggregation. As a consequence of regional coherence inmeteorology, ignition, daily fire spread, and fire extinction events wereoften synchronized across different fires in interior Alaska. At a regionalscale, the sum of positive VPD anomalies during the fire season waspositively correlated with annual burned area during the NARR era(1979–2011; R² = 0.45). Some of the largest fires we mapped had slowinitial growth, indicating opportunities may exist for suppression effortsto adaptively manage these forests for climate change. The results of ourspatiotemporal analysis provide new information about temporal and spatialdynamics of wildfires and have implications for modeling the terrestrialcarbon cycle.

[学科分类] 地球化学与岩石