Abstract
The apparent decline in the global incidence of fire between 1996 and 2015, as measured by satellite-observations of burned area, has been related to socioeconomic and land use changes. However, recent decades have also seen changes in climate and vegetation that influence fire and fire-enabled vegetation models do not reproduce the apparent decline. Given that the satellite-derived burned area datasets are still relatively short (<20 years), this raises questions both about the robustness of the apparent decline and what causes it. We use two global satellite-derived burned area datasets and a data-driven fire model to (1) assess the spatio-temporal robustness of the burned area trends and (2) to relate the trends to underlying changes in temperature, precipitation, human population density and vegetation conditions. Although the satellite datasets and simulation all show a decline in global burned area over ~20 years, the trend is not significant and is strongly affected by the start and end year chosen for trend analysis and the year-to-year variability in burned area. The global and regional trends shown by the two satellite datasets are poorly correlated for the common overlapping period (2001–2015) and the fire model simulates changes in global and regional burned area that lie within the uncertainties of the satellite datasets. The model simulations show that recent increases in temperature would lead to increased burned area but this effect is compensated by increasing wetness or increases in population, both of which lead to declining burned area. Increases in vegetation cover and density associated with recent greening trends lead to increased burned area in fuel-limited regions. Our analyses show that global and regional burned area trends result from the interaction of compensating trends in controls of wildfire at regional scales.
Highlights
Despite the occurrence of major catastrophic wildfires in recent years (Cruz et al 2012, Dennison et al 2014, Stephens et al 2014, Bowman et al 2017), total global burned area (BA) apparently declined between 1996 and 2015 (Van Lierop et al 2015, Doerr and Santín 2016, Andela et al 2017)
The global and regional trends shown by the two satellite datasets are poorly correlated for the common overlapping period (2001–2015) and the fire model simulates changes in global and regional burned area that lie within the uncertainties of the satellite datasets
In the version of the SOFIA model applied here, burned area (BA) was simulated on monthly time steps per 0.25° grid cells based on the fractional coverage of different land cover types (LC), and on controlling functions based on the predictors FAPAR, vegetation optical depth (VOD), wet days (WET), TMAX, diurnal temperature range (DTR) and population density (PD): BA = å LCi ⁎f (FAPAR)i⁎f (VOD)i⁎f (WET)i⁎f (TMAX)i⁎f (DTR)i⁎f (PD) i = {T, S, H, C}
Summary
Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Matthias Forkel1 , Wouter Dorigo1 , Gitta Lasslop2 , Emilio Chuvieco3 , Stijn Hantson4 , Angelika Heil5, Irene Teubner1 , Kirsten Thonicke6 and Sandy P Harrison7 Keywords: fire, greening, VOD, FAPAR, fuel, dynamic global vegetation models, multi-temporal trend analysis
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