Fire‐induced albedo change and surface radiative forcing in sub‐Saharan Africa savanna ecosystems: Implications for the energy balance

Abstract

Surface albedo is a critical parameter that controls surface energy balance. In dryland ecosystems, fires play a significant role in decreasing surface albedo, resulting in positive radiative forcing. Here we investigate the long‐term effect of fire on surface albedo. We devised a method to calculate short‐, medium‐, and long‐term effect of fire‐induced radiative forcing and their relative effects on energy balance. We used Moderate Resolution Imaging Spectroradiometer (MODIS) data in our analysis, covering different vegetation classes in sub‐Saharan Africa (SSA). Our analysis indicated that mean short‐term fire‐induced albedo change in SSA was −0.022, −0.035, and −0.041 for savannas, shrubland, and grasslands, respectively. At regional scale, mean fire‐induced albedo change in savannas was −0.018 and −0.024 for northern sub‐Saharan of Africa and the southern hemisphere Africa, respectively. The short‐term mean fire‐induced radiative forcing in burned areas in sub‐Saharan Africa (SSA) was 5.41 W m−2, which contributed continental and global radiative forcings of 0.25 and 0.058 W m−2, respectively. The impact of fire in surface albedo has long‐lasting effects that varies with vegetation type. The long‐term energetic effects of fire‐induced albedo change and associated radiative forcing were, on average, more than 19 times greater across SSA than the short‐term effects, suggesting that fires exerted far more radiative forcing than previously thought. Taking into account the actual duration of fire's effect on surface albedo, we conclude that the contribution of SSA fires, globally and throughout the year, is ~0.12 W m−2. These findings provide crucial information on possible impact of fire on regional climate variability.

Increases in Land Surface Temperature in Response to Fire in Siberian Boreal Forests and Their Attribution to Biophysical Processes

“…In North American boreal forests where high-intensity fires remove the canopy and reveal snow cover, albedo increases following fire and results in a negative radiative forcing between À5.0 and À1.3 W m À2 (Huang et al, 2015;Randerson et al, 2006;Rogers et al, 2015). In contrast, in dryland ecosystems such as savannas and grasslands, where frequent high severity fires are prevalent, postfire albedo decreases for as long as several years and causes a positive radiative forcing between 0.1 and 0.54 W m À2 (Dintwe et al, 2017;Gatebe et al, 2014). Such differences in climate feedback between these two boreal regions are related to species traits, fire regimes, and snow climatology (Rogers et al, 2015).…”

“…In Siberian boreal forests where lower-intensity surface fires are common, the postfire albedo increase is less dramatic and caused by a relatively weak negative radiative forcing of À0.53 W m À2 ( Figure S9). Despite the relatively small radiative forcing changes due to savanna or grassland fires, their global contribution is important because they contribute the most to global BA and greenhouse gas emissions (Dintwe et al, 2017;van der Werf et al, 2017). In contrast, in dryland ecosystems such as savannas and grasslands, where frequent high severity fires are prevalent, postfire albedo decreases for as long as several years and causes a positive radiative forcing between 0.1 and 0.54 W m À2 (Dintwe et al, 2017;Gatebe et al, 2014).…”

“…These results are robust using both the space-for-time substitution approach used here (comparing two adjacent pixels) and a space-and-time approach, in which temporal climate variability is considered (Text S2 and Figure S7). Time series plots of NDVI, albedo, and LST indicated a strong influence of climate on LST and slow ecosystem recovery times (Text S2 and Figure S8), and this precluded the temporal approach (whereby a burned pixel is compared to itself in the absence of fire) used for some studies in savanna ecosystems (Dintwe et al, 2017).…”

“…Such differences in climate feedback between these two boreal regions are related to species traits, fire regimes, and snow climatology (Rogers et al, 2015). In contrast, in dryland ecosystems such as savannas and grasslands, where frequent high severity fires are prevalent, postfire albedo decreases for as long as several years and causes a positive radiative forcing between 0.1 and 0.54 W m À2 (Dintwe et al, 2017;Gatebe et al, 2014). Despite the relatively small radiative forcing changes due to savanna or grassland fires, their global contribution is important because they contribute the most to global BA and greenhouse gas emissions (Dintwe et al, 2017;van der Werf et al, 2017).…”

Índices Espectrais e Temperatura de Superfície em Áreas Queimadas no Parque Estadual do Araguaia em Mato Grosso

“…Por milhares de anos, o fogo tem sido um importante integrante dos processos biogeoquímicos, influenciando nas interações terra-atmosfera, estando presente em forma de instrumento de manejo em mais de 50% dos ecossistemas terrestres (Liu et al, 2016;Dintwe et al, 2017). Ele pode ser de origem natural, provocado por combustão espontânea ou incidência de raios e impulsionado por fatores como a umidade do ar, precipitação e velocidade do vento, bem como de origem antrópica, podendo gerar grandes incêndios florestais quando ocorre de forma acidental ou até mesmo criminosa (Clemente et al, 2017;Forkel et al, 2017).…”