Relative humidity and agricultural activities dominate wildfire ignitions in Yunnan, Southwest China: Patterns, thresholds, and implications

Wildfires are land-surface processes and ecological disturbances occurring around the world. The wildfire regime in Yunnan Province of Southwest China is recognized as similar to that of the adjoining Indo-China Peninsula, a global hotspot for wildfires. However, the ignition mechanisms in this region remain unclear, with interactions among ecosystem features, local agricultural activities, and fire weather controlled by the West Pacific and Indian Ocean monsoons. Based on the ground records of 5145 confirmed wildfire events in Yunnan during the period of 2003-2015, we used a logistic regression model to estimate the local environmental controls on wildfire ignitions. Results highlighted the primary role of meteorology-driven characters, especially the prevalent importance of daily minimum relative humidity across the region. The threshold of the relative humidity was 37.48% +/- 15.60% for the 50% ignition probability. Relative humidity also dominated ignition over years, with fuel conditions relatively stable and playing a minor role in contrast to the inter-annual climate changes. Moreover, agriculture-related ignition comprised most wildfire records, and human activities deeply shaped the spatiotemporal patterns of ignition. The distance to the nearest village was the primary factor during the beginning of the agricultural season, with a farming radius of 1.2 km as a key threshold for ignition. The complementary roles among influential factors were prominent at county scale. Among counties, the variation of ignition mechanisms corresponded to the influence paths of the two monsoons. This study highlights the importance of ground wildfire records in deriving critical wildfire ignition information such as environmental thresholds and change rates, which can provide important insights for sustainable forest management in this region, including wildfire monitoring, ignition control, fuel structure adjusting, and implementing differentiated strategies for fire prevention with regard to the environmental contexts.

Automated summary

Based on the ground records of 5145 confirmed wildfire events in Yunnan during the period of 2003-2015, meteorology-driven factors, especially daily minimum relative humidity, played a crucial role in wildfire ignitions. Agriculture-related ignitions comprised most wildfire records, with human activities shaping the spatiotemporal patterns of ignition.