Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

Abstract

The albedo change caused by fires and the subsequent succession is spatially heterogeneous, leading to the need to assess the spatiotemporal variation of surface shortwave forcing (SSF) as a component to quantify the climate impacts of high-latitude fires. We used an image reconstruction approach to compare postfire albedo with the albedo assuming that no fires had occurred. Combining the fire-caused albedo change from the 2001-2010 fires in interior Alaska and the monthly surface incoming solar radiation, we examined the spatiotemporal variation of SSF in the early successional stage of approximately 10 years. Our results showed that although postfire albedo generally increased in fall, winter, and spring, some burned areas could show an albedo decrease during these seasons. In summer, the albedo increased for several years and then declined again. The spring SSF distribution did not show a latitudinal decrease from south to north as previously reported. The results also indicated that although the SSF is usually largely negative in the early successional years, it may not be significant during the first postfire year. The annual 2005-2010 SSF for the 2004 fire scars was -1.30, -4.40, -3.31, -4.00, -3.42, and -2.47 W·m −2 , respectively. The integrated annual SSF map showed significant spatial variation, with a mean of -3.15 W·m −2 , a standard deviation of 3.26 watts per square metre (W·m −2 ), and 16% of burned areas having positive SSF. Our results suggest that boreal deciduous fires would be less positive for climate change than boreal evergreen fires. Future research is needed to comprehensively investigate the spatiotemporal radiative and nonradiative forcings to determine the effect of boreal fires on the climate.Résumé : La modification de l'albédo causée par les feux et la succession végétale subséquente est spatialement hétérogène. Il est donc nécessaire d'avoir accès à la variation spatio-temporelle du forçage aux courtes longueurs d'onde de la surface en tant que composante pour quantifier les impacts des feux aux latitudes élevées sur le climat. Nous avons utilisé la reconstruction d'image pour comparer l'albédo après feu à celui qu'on aurait pu mesurer s'il n'y avait pas eu de feu. En combinant la modification de l'albédo causée par les feux de 2001 à 2010 à l'intérieur de l'Alaska et le rayonnement solaire mensuel incident à la surface, nous avons étudié la variation spatio-temporelle du forçage au stade précoce de succession sur une période d'environ 10 ans. Nos résultats ont montré que, bien que l'albédo après feu ait généralement augmenté à l'automne, en hiver et au printemps, il pouvait diminuer durant ces saisons dans certaines zones brûlées. En été, l'albédo a augmenté pendant plusieurs années et diminué à nouveau par la suite. Il n'y a pas eu de diminution latitudinale de la distribution printanière du forçage, du sud vers le nord, comme cela a déjà été rapporté. Les résultats indiquent aussi que même si le forçage est habituellement largement négatif durant les premières années de la succe...

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). Fire-induced albedo change and associated changes in radiative forcing vary significantly in duration, magnitude, and sign depending on ecosystem type and fire regimes.…”

“…Fire-induced albedo change and associated changes in radiative forcing vary significantly in duration, magnitude, and sign depending on ecosystem type and fire regimes. 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 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).…”

Evidence for fire in the Pliocene Arctic in response to amplified temperature

“…Studies of the impact of wildfire on surface energy balance in present-day northern ecosystems have revealed the complexity of predicting wildfire's impact on climate. Ecosystems exhibit changing responses through time from the scale of years post-burning (Randerson et al, 2006;Bonan, 2008;French et al, 2016) to seasonal (Huang et al, 2014) and even diurnal differences post- deforestation that may impact net wildfire feedback to climate (Schultz et al, 2017). The radiative response to wildfire changes across latitudinal gradients (Jin et al, 2012) and between local and global scales (Ward et al, 2012;Liu et al, 2019).…”

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

“…Gatebe et al [2014] used unburned neighboring pixels as control, whereas in our study we compared a pixel to itself (equations (2) and (3)) in neighboring year where it did not burn. The approach of comparing two neighboring pixels is commonly used [e.g., Gatebe et al, 2014;Huang et al, 2014;Lyons et al, 2008;Myhre et al, 2005;Samain et al, 2008], but it does not take into account heterogeneity of the land surface. That is, it assumes homogenous vegetation cover.…”

“…Fire-induced albedo change and associated radiative forcing have started to attract the attention of ecologists, climatologists, and policy makers [López-Saldaña et al, 2014]. Recent studies show that in boreal forest, postfire albedo increases at weekly to yearly temporal scales and results in negative radiative forcing [Flannigan et al, 2009;Huang et al, 2014;Jin et al, 2012;Lyons et al, 2008;Oris et al, 2013;Randerson et al, 2006]. However, in dryland ecosystems such as savannas and grasslands, postfire albedo decreases and causes positive radiative forcing at weekly to yearly temporal scales [Gatebe et al, 2014;Jin and Roy, 2005;López-Saldaña et al, 2014].…”