<![CDATA[Peatland ecosystems across tropical regions are prone to severe fires during drought periods, making timely and accurate early drought monitoring vital for fire risk mitigation. This study assesses drought conditions in Siak Regency, Indonesia, employing the Normalized Difference Drought Index (NDDI) derived from Sentinel-2 satellite imagery using the Google Earth Engine (GEE) platform. NDDI, which combines indices of vegetation greenness (NDVI) and moisture (NDWI), was used to map peatland dryness. The research analysed NDDI patterns for each month from 2019 to 2024 and was tested against MODIS and VIIRS fire hotspots both spatially, by overlaying hotspots on classified drought maps, and temporally, using Spearman correlation. The results show that the two approaches produced an informative contrast. Spatially, fire was concentrated strongly in the driest classes: on average 91% of hotspots (85% pooled across all 507 detections made) fell within the severe and extreme drought classes (NDDI > 0.25). A chi-square test confirmed that this distribution was clearly not a question of chance (chi-square = 96.1, p < 0.001). Temporally, however, the month-to-month correlation was weak (mean rho = 0.24), so the surface signal alone does not set fire timing within a particular year. An independent CHIRPS rainfall record confirmed the wet- and dry-year ranking and linked annual rainfall to burnt areas (rho = -0.94, p = 0.005). NDDI is therefore a reliable indicator of areas where peatland is fire-prone, and is best used as a spatial fire-susceptibility layer within a multi-factor early-warning system, being transferable to other tropical peatlands.]]>
