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

Abstract

Abstract. Climate-driven changes in the fire regime within boreal forest ecosystems are likely to have important effects on carbon cycling and species composition. In the context of improving fire management options and developing more realistic scenarios of future change, it is important to understand how meteorology regulates different aspects of fire dynamics, including ignition, daily fire spread, and cumulative annual burned area. Here we combined ModerateResolution Imaging Spectroradiometer (MODIS) active fires (MCD14ML), MODIS imagery (MOD13A1) and ancillary historic fire perimeter information to produce a data set of daily fire spread maps for Alaska during 2002-2011. This approach provided a spatial and temporally continuous representation of fire progression and a precise identification of ignition and extinction locations and dates for each wildfire. The fire-spread maps were analyzed with daily vapor pressure deficit (VPD) observations from the North American Regional Reanalysis (NARR) and lightning strikes from the Alaska Lightning Detection Network (ALDN). We found a significant relationship between daily VPD and likelihood that a lightning strike would develop into a fire ignition. In the first week after ignition, above average VPD increased the probability that fires would grow to large or very large sizes. Strong relationships also were identified between VPD and burned area at several levels of temporal and spatial aggregation. As a consequence of regional coherence in meteorology, ignition, daily fire spread, and fire extinction events were often synchronized across different fires in interior Alaska. At a regional scale, the sum of positive VPD anomalies during the fire season was positively correlated with annual burned area during the NARR era ; R 2 = 0.45). Some of the largest fires we mapped had slow initial growth, indicating opportunities may exist for suppression efforts to adaptively manage these forests for climate change. The results of our spatiotemporal analysis provide new information about temporal and spatial dynamics of wildfires and have implications for modeling the terrestrial carbon cycle.

The influence of daily meteorology on boreal fire emissions and regional trace gas variability

“…VPD, derived from a combination of temperature and relative humidity, was slightly better than temperature as a predictor for FRP and burned area but had about the same level of performance for the other fire time series. The relatively high performance of VPD as a predictor for burned area observed here is consistent with earlier work indicating that VPD anomalies in interior Alaska synchronizes spread rates across multiple fires [ Sedano and Randerson , ].…”

“…Here we found that temperature and vapor pressure deficit were the most important meteorological fields to explain daily fire activity during the summer of 2013. The importance of these variables has been noted in past studies at different temporal and spatial scales [ Flannigan and Harrington , ; Bessie and Johnson , ; Duffy et al ., ; Sedano and Randerson , ]. Monthly burned area in different Canadian provinces was shown to vary considerably as a function of extended periods of days with low precipitation or relative humidity [ Flannigan and Harrington , ].…”

“…Weather and climate strongly influence fire dynamics in boreal forests on time scales of hours to decades [ Johnson , ]. Ambient weather conditions control lightning ignition probability [ Latham and Schlieter , ; Nash and Johnson , ; Anderson , ] and fire spread rates [ Sedano and Randerson , ] through their influence on convection, fire weather, and fuel moisture. The moisture content of fine surface fuels rapidly responds to variations in vapor pressure deficit over a period of hours or days, whereas the moisture content of deeper soil layers responds to the cumulative effects of precipitation and evapotranspiration over the course of the fire season [ Van Wagner , ].…”

Plant responses to increasing CO 2 reduce estimates of climate impacts on drought severity

“…Fire weather indices used in climate change studies often rely on atmosphere-centric metrics and variables, and this choice may not adequately capture the response of live fuels or deeper organic duff layers. Further, this study illustrates that relative humidity, a variable known to influence many aspects of fire behavior (31), responds to the influence of atmospheric CO 2 on plant processes by an amount equal to or greater than the radiative effects of CO 2 ( Fig. S1 and Table S3).…”

Atmospheric and Surface Climate Associated With 1986–2013 Wildfires in North America

“…Enhanced Q h also steepens the vapor pressure gradient and thus VPD, which promotes further drying of fuels and the soil. This positive feedback enhances the potential for and behavior of wildfire (Potter, , ; Sedano & Randerson, ; Snyder et al, , ). In water‐limited areas, the seasonal peaks in ϕ sw , R net , Q h , and VPD generally coincide with high incidence of wildfire.…”