Ecoregion-Based Fire Weather Index Patterns Prior to Wildfire Events in Sumatra

Abstract

Wildfires in Sumatra are shaped by meteorological conditions and the diverse biophysical characteristics of its ecoregions. This study investigates the temporal patterns of the Fire Weather Index (FWI) during the seven days preceding wildfire events across six major ecoregions of Sumatra, using ERA5-Land meteorological data and MODIS hotspot records for the period 2015–2024. FWI was computed following the Canadian Forest Fire Weather Index System (CFFWIS), calibrated for the Indonesian tropics. Results show that the peat swamp forest (PSF) and freshwater swamp forest (FWF) ecoregions consistently recorded the highest absolute values, with gradual increasing trends that reflect long-term moisture deficit accumulation. Conversely, the highland ecoregions (tropical pine forest or TPF and montane rainforest or MRF) exhibited low initial values followed by rapid increases approaching the event day, indicating dependence on short-term weather anomalies. The Sunda Shelf mangrove (SSM) displayed rapid response to wind speed changes, while the lowland rainforest (LRF) showed acceleration only during the final three days before events. Spatially, southern Sumatra exhibited higher climatological FWI normals and larger positive anomalies on wildfire days compared to the north. These findings underscore the need for ecoregion-specific FWI thresholds and early warning systems.