Drought Risk Assessment and Monitoring of Ilocos Norte Province in the Philippines Using Satellite Remote Sensing and Meteorological Data

Drought has been known to be a natural hazard reflecting geographic and climatic characteristics. Satellite technology advancements have benefited drought assessment and monitoring to formulate plans for dealing with this slow-onset disaster. However, combining satellite remote sensing (RS) and meteorological data for drought monitoring is lacking in the literature. This study uses satellite RS and meteorological-based drought indicators to assess drought risk in the Ilocos Norte, Philippines. Data analysis included the retrieval of vegetation conditions using Sentinel-1 and Sentinel-2 data. The standardized precipitation index (SPI) and Keetch-Byram drought index (KBDI) were calculated to account for climatic variabilities. Results revealed that the Sentinel-1 backscatter coefficient decreased by -2 dB in the cropland area, indicating crop growth irregularities compared to grassland areas. These irregularities were supported by Sentinel-2 normalized difference vegetation index (NDVI) strong fluctuations during the two-year observation period. A significant coefficient of determination (R-2 > 0.60) between the Sentinel-1 backscatter coefficient and Sentinel-2 NDVI was observed for the study area. On the one hand, only KBDI significantly correlated (R-2 > 0.60) with the cropland area's RS data-derived drought indicators. These results revealed RS data variability for drought risk management but are still valuable for developing an early warning system.