Siberian taiga and tundra fire regimes from 2001–2020

Abstract

Circum-boreal and -tundra systems are crucial carbon pools that are experiencing amplified warming and are at risk of increasing wildfire activity. Changes in wildfire activity have broad implications for vegetation dynamics, underlying permafrost soils, and ultimately, carbon cycling. However, understanding wildfire effects on biophysical processes across eastern Siberian taiga and tundra remains challenging because of the lack of an easily accessible annual fire perimeter database and underestimation of area burned by MODIS satellite imagery. To better understand wildfire dynamics over the last 20 years in this region, we mapped area burned, generated a fire perimeter database, and characterized fire regimes across eight ecozones spanning 7.8 million km2 of eastern Siberian taiga and tundra from ∼61–72.5° N and 100° E–176° W using long-term satellite data from Landsat, processed via Google Earth Engine. We generated composite images for the annual growing season (May–September), which allowed mitigation of missing data from snow-cover, cloud-cover, and the Landsat 7 scan line error. We used annual composites to calculate the difference Normalized Burn Ratio (dNBR) for each year. The annual dNBR images were converted to binary burned or unburned imagery that was used to vectorize fire perimeters. We mapped 22 091 fires burning 152 million hectares (Mha) over 20 years. Although 2003 was the largest fire year on record, 2020 was an exceptional fire year for four of the northeastern ecozones resulting in substantial increases in fire activity above the Arctic Circle. Increases in fire extent, severity, and frequency with continued climate warming will impact vegetation and permafrost dynamics with increased likelihood of irreversible permafrost thaw that leads to increased carbon release and/or conversion of forest to shrublands.

Permafrost Degradation and Its Hydrogeological Impacts

“…During the last decade, at many locations in interior Alaska, there was no freeze up of the active layer. The proximity of the exceptionally ice-and organicrich soil horizons to the ground surface, typical for the Arctic and Boreal zones, makes ground thermal regimes very sensitive to disturbances from the development of landscape processes, strongly impacting the stability of ecosystems and infrastructures [83][84][85]. In many regions, SSTs have been formed or are forming (e.g., [10]).…”

We Must Stop Fossil Fuel Emissions to Protect Permafrost Ecosystems

“…This can stimulate organic matter decomposition and hydrological export for decades after the wildfire (Grosse et al, 2011;Rocha and Shaver, 2011;Carey et al, 2019;Meredith et al, 2019;Abbott et al, 2021b;Bruhwiler et al, 2021). Permafrost wildfires are expanding northward and even burning through the winter (Holloway et al, 2020;McCarty et al, 2020;Scholten et al, 2021;Veraverbeke et al, 2021;Talucci et al, 2022).…”

“…Additionally, many of these proposed solutions may be ineffective or counterproductive in the new conditions created by anthropogenic climate change. For example, the survival of large herds of herbivores could be negatively affected by shifts in forage and extreme weather events (Forbes et al, 2016;Zarnetske et al, 2021), and carbon uptake from tree planting can be erased by temperatureinduced mass mortality and an intensifying wildfire regime (Hammond et al, 2022;Talucci et al, 2022). Even if these interventions achieved their climate goals, they would threaten more than half of remaining intact ecosystems globally (Watson et al, 2018;Díaz et al, 2019).…”

Increasing threat of wildfires: the year 2020 in perspective: A Global Ecology and Biogeography special issue

“…On almost every continent on Earth, wildfire seasons of unparalleled size in the modern era have occurred in recent years (Duane et al, 2021). The year 2020 exemplified this trend, with wildfire seasons encompassing 14 million hectares (Mha) in Siberia, including a record burned area in the Arctic Circle (Duane et al, 2021;McCarty et al, 2020;Talucci et al, 2022); 7.5 Mha of temperate Eucalyptus forest in Australia during the 2019/20 Austral fire season (of 27 Mha total for this forest biome, 30%), which represents a globally unprecedented extent of temperate forest biome (Boer et al, 2020;Bowman et al, 2021); nearly 4 Mha, or almost one-third, of the Brazilian Pantanal (Libonati et al, 2021;Marengo et al, 2021); and over 2.5 Mha in the western USA (Higuera & Abatzoglou, 2021).…”