Abstract:

Objective: This study aims to reveal the spatiotemporal distribution relationships between forest and grassland fires and meteorological factors in Sichuan Province. It identifies the key meteorological factor combinations driving fire distribution, defines Foehn-prone periods, and analyzes the underlying atmospheric circulation mechanisms, providing a theoretical reference for developing scientific fire prevention strategies. Method: Based on MODIS active fire data and ERA5 meteorological data from 2005 to 2024, combined with land use and topographical data, the tools such as ArcGIS 10.8.2, Origin 2024, Excel 2021, and SPSS 27 were employed. First, the forest and grassland were distinguished from non-forest and non-grassland areas via land use data and fire points were extracted. Then, statistical analyses are conducted to characterize the distribution of fire occurrence counts at the monthly and spatial scales, respectively. Subsequently, the monthly spatial distributions of wind direction, average wind speed, average precipitation, average relative humidity, average temperature, and temperature differences between adjacent months were analyzed. Finally, the correlation between meteorological factors and fires was comprehensively explored, and thereby its accuracy was verified. The Foehn-prone seasons in Sichuan Province were clarified by generalizing judgment criteria and coarsening the time scale, and determining monthly-scale Foehn in Sichuan Province. Result: 1) Approximately 86.9% of forest and grassland fires in Sichuan Province occurred from January to May and in December (winter and spring). Spatially, about 97.66% of the Province’s total fires were concentrated in southwest Sichuan (Panzhihua City, Liangshan Yi Autonomous Prefecture) and northwest Sichuan (Ganzi Tibetan Autonomous Prefecture, Aba Tibetan and Qiang Autonomous Prefecture), with a higher frequency in southwest Sichuan than in northwest Sichuan. 2) Comparative analysis showed that across different regional and temporal combinations in Sichuan Province, only the winter and spring seasons in southwest and northwest Sichuan exhibit a distinct meteorological pattern characterized by high average wind speed, low precipitation, low relative humidity, significant temperature rise, and the dominance of southwesterly and southerly winds. 3) The number of fires was positively correlated with average wind speed, the monthly count of southwesterly winds, and the monthly count of southerly winds (ρ=0.923^**, P<0.001; ρ=0.930^**, P<0.001; ρ=0.804^**, P=0.002). Conversely, it was negatively correlated with average temperature, average precipitation, and average relative humidity (ρ=?0.643^*, P=0.024; ρ=?0.809^**, P=0.001; ρ=?0.979^**, P<0.001). 4) The winter and spring seasons in southwest and northwest Sichuan satisfy the criteria for “Foehn seasons”. Conclusion: This study reveals the spatiotemporal pattern of forest and grassland fires in Sichuan. They are temporally concentrated in winter and spring and spatially focused in the southwest and northwest regions (with higher frequency in the southwest). The winter and spring periods of southwestern and northwestern Sichuan have be defined as “Foehn seasons”. The study concludes that the specific meteorological combination—dominated by southwesterly and southerly winds, high wind speed, low precipitation, low humidity, and significant warming, coupled with frequent Foehn events, constitutes the key driver for the concentration of fires.

Key words: forest and grassland fires, meteorological factors, spatiotemporal distribution, atmospheric circulation, Foehn effect, Sichuan Province