Monitoring drought vulnerability using multispectral indices observed from sequential remote sensing (Case Study: Tuy Phong, Binh Thuan, Vietnam)

This study applies multispectral band ratios to examine vegetation density and vegetation health to assess drought conditions over nearly 30 years (1989-2016) in Tuy Phong district, Binh Thuan province, Vietnam using a sequence of Landsat imagery (TM and OLI). Our research area has a distinctive climate, characterized by arid and semiarid areas adjacent to Binh Thuan's coastline. Drought is likely intensified by rain shadow effects of the Central Highlands (part of the Truong Son- or the Annamese Cordillera, positioned immediately west of the province). The seasonal Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) were calculated to derive three other indices: Vegetation Condition Index (VCI), Temperature Condition Index (TCI), and Vegetation Health Index (VHI). Results show that approximately two-thirds of Tuy Phong district was influenced by mid-to-severe drought. During the dry season (November to the following April), severity of drought has increased both intensively and extensively toward the North. Hypotheses testing of correlation between LST and NDVI also revealed a significantly negative relationship - increasing surface temperature and decreasing NDVI. To validate our results, we applied the same procedure for generating the VHI from MODIS data. Despite the absence of historical datasets for our region, Landsat data shows many advantages in monitoring drought in remote and small areas compared to MODIS. Our research strategies may be effective in other regions without sufficient climatic records for conventional climatic analysis.