# How Environmental Factors Affect Forest Fire Occurrence in Yunnan Forest Region
###### Abstract  
Forest fire is an ecosystem regulating factor and affects the stability, renewal, and succession of forest ecosystems. However, uncontrolled forest fires can be harmful to the forest ecosystem and to the public at large. Although Yunnan, China is regarded as a global hotspot for forest fires, a general lack of understanding prevails there regarding the mechanisms and interactions that cause forest fires. A logistic regression model based on fire points in Yunnan detected by satellite in 2005-2019 was used to estimate how environmental factors in local areas affect forest fire events. The results show that meteorology is the dominant cause of the frequent forest fires in the area. Other factors of secondary importance are the daily minimum relative humidity and the daily maximum temperature. When using the logistic regression model based on the data of fire points in Yunnan over the period 2005-2019, the key threshold for the daily minimum relative humidity is 28.07% \(\pm\) 11.85% and the daily maximum temperature is 21.23 \(\pm\) 11.15 \({}^{\circ}\)C for a forest fire probability of 50%. In annual and monthly dynamic trends, the daily minimum relative humidity also plays a dominant role in which combstible substance load remains relatively stable from January to March, and the impact on forest fire becomes greater in April, May, and June, which plays a secondary role compared with the interannual climate. The maximum daily temperature ranks third in importance for forest fires. At the county level, minimum relative humidity and maximum temperature are the top two factors influencing forest fires, respectively. Meanwhile, the differences in forest fire points between counties correspond to the pathways of the two monsoons. This study applies quantitative expressions to reveal the important environmental factors and mechanisms that cause forest fires. The results provide a reference for monitoring and predicting forest fires. forest fire; logistic regression model; environmental factors; key threshold; quantitative expressions 202220220220220220220220220220220220202202020220220202202022020220202202022020220202022020220202202202022020220202202022023131354331313313131313131  
the widely distributed Pinus yunnanensis forest and mixed forests of green broad-leaved trees [25]. In Yunnan, the monsoon is a key factor influencing forest fires. The humid summer and autumn climate is a major feature of monsoons from the western Pacific Ocean and the Indian Ocean [26]. In winter and spring, the monsoon recedes and is replaced by warm, dry southwesterly winds [27]. Both ground monitoring and remote sensing indicate that this is the season of frequent forest fires in Yunnan [28]. Human activity is another major cause of frequent forest fires in Yunnan. In fact, slash-and-burn agriculture has been practiced in Yunnan for a long time [29; 30], and many Chinese cultural traditions (e.g., burning joss paper, burning incense, and setting off firecrackers) are potential sources of fire. The environmental variables that affect forest fire occurrence in Yunnan have rarely been investigated, so limited information is available about the causes and effects of forest fires in Yunnan. By using a remote-sensing method, [PERSON] et al. [31] determined that the distance of residences and roads from the forest zone is a key factor in the occurrence of forest fires. [PERSON] et al. [32] investigated lake sediments in Yunnan and found evidence of forest fire events over the last 20,000 years. They pointed out that climate conditions, combustible substances, and human activities played a crucial role in the occurrence of forest fires. Based on three years of county-level forest fire records from various provinces of China, [PERSON] et al. [24] concluded that the presence of combustible substances was the main factor influencing the occurrence of forest fires in Yunnan.