Projections of wildfire risk and activities under 1.5 °C and 2.0 °C global warming scenarios

Abstract

Wildfires are important ecosystem processes that have a significant impact on terrestrial vegetation, environment, and climate. This study investigates how future wildfire risk and activities could change under 1.5 °C and 2.0 °C warming scenarios relative to pre-industrial levels using a modified McArthur Forest Fire Danger Index (FFDIn) and the CLM4.5-BGC land surface model. Sixteen Earth System Models (ESMs) from CMIP5 and CMIP6 were employed to supply the variables of climate change under low, middle, and high greenhouse emission scenarios in the 1.5 °C and 2.0 °C scenarios. The ensemble means from the FFDIn and results from the CLM4.5-BGC with multiple forcings show that the dry areas in the southwestern US, Brazilian Highlands, and Arabian islands are projected to face higher wildfire risk with larger burned areas and more carbon emissions under a warmer climate. The Congo Basin and part of the Amazon could have a lower wildfire risk with smaller burned areas and less carbon emissions. The absolute changes in the projected FFDIn are small, although large increases are observed in boreal areas, particularly in the winter and spring. Burned area and carbon emissions are projected to increase in general in the boreal area but decrease in northeastern Asia. Compared to the 1.5 °C scenario, the wildfire risk and burned area levels are projected to increase under the 2.0 °C scenario except in the western Amazon. However, fire carbon emissions are projected to decrease more in tropical areas under the 2.0 °C scenario. The different change directions in eastern North America and eastern China produced by the FFDIn and CLM4.5-BGC suggest the potential effect of non-meteorological elements on fire activities.

Wind Driving Longer Uncontrolled Large Fire Duration in the Western United States

“…Furthermore, the long duration of large wildfires may result from strained fire-fighting resources or fire management strategies 7,31 , which is not included in our MLR models. With recent studies projecting an increasing fire activity or risk in the future over the western US [32][33][34][35][36] , our study has profound implications for decision makers considering the impacts of potential changes in background wind speed and the positive fire feedback on wind speed on uncontrolled large fire duration.…”

Enhanced Light Absorption and Elevated Viscosity of Atmospheric Brown Carbon through Evaporation of Volatile Components

“…Accurate prediction of the atmospheric environment and radiative forcing of the climate requires an improved understanding of the composition and optical properties of biomass burning aerosols, which contain a significant amount of light-absorbing organic components termed brown carbon (BrC). − As the frequency and intensity of wildfires increase as a result of a warmer and drier climate, BrC becomes a profound contributor to the overall radiative forcing. − This is attributed to its capacity to absorb solar radiation within the UV and visible wavelengths. ,− Additionally, the widespread use of biomass fuels and practices of agricultural burning in developing countries amplifies BrC emissions and its significance. − The upsurge in BrC aerosols from biomass burning (BB) disturbs various climate and atmospheric processes, including long-range transport of atmospheric pollutants, cloud condensation and ice nucleation, alterations in snow and ice albedo, and reduced photodegradation rates. − The extent to which BB-BrC aerosols influence these processes remains uncertain, which makes it challenging for atmospheric models to accurately project their global impact both presently and in the future.…”

“…The reference carbon numbers (n C 0 ) and b coefficients for CHO and CHNO species are reported in Table 1 in the work of Li et al 106 The viscosities of the CHO and CH species (log 10 (η, Pa•s)) are estimated using the Vogel−Tammann−Fulcher equation. 107 = e T D T T /( ) 0 0 (7) where η ∞ (Pa•s) represents the low limit viscosity value (10 −5 Pa•s) at very high temperatures; T is the ambient temperature (298 K); T 0 is the Vogel temperature calculated as T 0 = 39.17 × T g /(D + 39.17). Here, D is the fragility parameter (assumed to have a value of 10), which describes the rate at which the dynamics of the compound slows down as T approaches the material's glass-transition T g temperature.…”