Spatio-temporal variation characteristics of global wildfires and their emissions

Abstract. Intense regional wildfires are a common occurrence in the context of climate warming and have progressively evolved into one of the major natural disasters in terrestrial ecosystems, posing a serious hazard to the atmosphere and climate change. We investigated the spatial distribution, intensity, emission changes, and meteorological differences of wildfires in different wildfire active and wildfire-prone regions globally based on multi-source satellite remote sensing fire data, emission data, and meteorological data in order to better understand the change trend of wildfire activity at multiple spatial and temporal scales. The findings demonstrate that while the wildfire burned area (BA) has decreased slowly over the last 20 years, the wildfire burned fraction (BF), the fire count (FC), and the fire radiative power (FRP) all exhibit pronounced regional and seasonal variations. The physical characteristics of wildfires, including the BF, FC and FRP, experience greater seasonal variation as latitude increases, with summer and autumn as the reasons with the most frequent wildfires worldwide. This study also shows that the emission declined substantially between 2012 and 2020 in Northern Canada, Alaska, and Northeast China, whereas it notably increased in the Siberia region during the same period, primarily due to a rise in summer emissions. The results based on classification show that the absolute amount of CO2 produced by wildfires is the largest, and the difference among regions is relatively small. Excluding CO2, aerosol emissions (the total of OC, TC, and BC) ranged from 78.6 % to 84.2 %, while the least significant air pollutants (the total of PM2.5, SO2, and NOx) ranged from 5.8 % to 11.7 %. The abundance of vegetation predominately affects the intensity change of wildfire development, while the weather conditions can also indirectly influence the incidence of wildfire by altering the growth condition of vegetation. Correspondingly, the increase in temperature in the northern hemisphere's middle and high latitude forest regions was primarily responsible for the increase in wildfires and emissions, while the change in wildfires in tropical regions was more influenced by the decrease in precipitation and relative humidity. This study contributes to the understanding of regional variations in wildfire activity and emission variability, and provides support for the control of wildfire activity across regions and seasons.