Upslope expansion of active fire detections weakened following intensified fire-prevention policies in the southeastern margin of the Tibetan Plateau

The southeastern margin of the Tibetan Plateau, including the Hengduan Mountains (HDM), is a hotspot of subtropical active fire occurrence. We analyzed MODIS active fire detections from 2001 to 2024 together with elevation, meteorological, population, policy, and Oceanic Niño Index (ONI) data using kernel density estimation, ordinary least squares regression, a 5-year moving-window Welch t-test, interrupted time-series (ITS) regression, random forest, and Spearman correlation. During 2001–2014, annual active fire counts increased markedly, particularly at 2000–3500 m, while mean fire elevation shifted upslope at 38.34 m yr−1 (p = 0.032). After 2015, both the overall increase and upslope shift weakened. After adjustment for ENSO variability, ITS showed a significant immediate reduction in annual active fire count associated with the 2014–2015 policy-intensification period (β = −342.30, p = 0.028), whereas the post-intervention slope change and ONI association were not significant. Drivers varied with elevation: human activity and atmospheric dryness were important at low elevations, humidity and drought stress at mid elevations, and wind-related variability at high elevations. These results support an association between intensified fire prevention and reduced active fire occurrence.