Fire activity and fire weather in a Lower Mekong subregion: association, regional calibration, weather–adjusted trends, and policy implications

Fire activity and fire weather in a fire–prone Lower Mekong subregion (mainly encompassing northern Thailand, eastern Myanmar, and northern Laos) were investigated over a long–term 20–year period (2003–2022) using multiple datasets (here, satellite–detected fires, gridded ERA5–based fire weather, gridded land cover, terrain elevation, slope, potential available biomass, and population density). Both fires and fire weather exhibit strong seasonality. In the dry season, fires are intensified, and fire weather promotes them. Dry–season fires contribute dominantly to total fires. Fire grouping was performed to cluster dry–season fires into groups. The log–logistic and exponential models were used to fit daily fine fuel moisture code and fire weather index of the Canadian Forest Fire Danger Rating System, respectively, together with daily fire activity. The calibrated thresholds of the two indices were determined using a slope–based method, partitioning each index into different danger levels. The new calibrated thresholds suggest fires in Lower Southeast Asia being more sensitive to fire weather than in Upper Southeast Asia. A generalized linear model based procedure was used to remove the effects of fire weather on trend (i.e., weather adjustment). The original trends in fire activity are significantly decreasing. The weather–adjusted trends in fire activity also show a decline, confirming effective regional fire management. Differences in the weather–adjusted trends between the first and second half periods suggest that Thailand has maintained effective fire management in the recent years. But Myanmar and Laos may need to strengthen their fire management especially in the forest and agricultural areas, respectively.