Drought Assessment of Rice in the Philippines using Enhanced Vegetation Index based Agricultural Drought Indices

Abstract. Agricultural drought has a considerable impact on agricultural productivity in the Philippines. This study evaluates the performance of agricultural drought indices: Standardized Vegetation and Temperature Ratio (SVTRe) and Vegetation Health Index (VHIe) derived from the Enhanced Vegetation Index (EVI) of the Moderate Resolution Imaging Spectroradiometer (MODIS) to assess drought conditions across the Philippines from 2000 to 2024. Using run theory, we quantified drought frequency, duration, and intensity, identifying drought-prone regions such as Cagayan Valley, Western Luzon, and Western Visayas. SVTRe recorded 15 to 20 incidents, and was more sensitive to moderate droughts, while VHIe recorded 15 to 30 events, capturing more extreme conditions. Both indices revealed consistent spatial and temporal drought patterns, with Mann-Kendall trend analysis indicating increased severity throughout the study period. SVTRe demonstrated higher overall accuracy (58.25%), whereas VHIe, achieved a higher hit rate (90.14%). Taken together, these indices offer complementary tools towards improving drought monitoring and enhancing agricultural resilience in the Philippines.