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.

Drought is a dry-weather event characterized by a deficit of water resources in a period of year due to less rainfall than normal or overexploitation. This insidious hazard tends to occur frequently and more intensively in sub-humid regions resulting in changes in the landscape, transitions in agricultural practices and other environmental-social issues. The study area is in the sub-humid region of the northern coastal zone of Binh Thuan province, Vietnam—Tuy Phong district. This area is indicated as a subject of prolonged droughts during 6-month dry seasons, which have occurred more frequently in recent years. Associated with economic transitions in agricultural practicing, urbanization, and industrialization, prolonged droughts have resulted in rapid changes in land use and land cover (LULC) in Tuy Phong, especially in three coastal communes: Binh Thanh, Lien Huong, and Phuoc The. A bi-temporal analysis using high-resolution data, the 2011 WorldView2 and the 2016 GeoEye1, was examined to assess LULC changes from observed severe droughts in those three communes. Results showed a dramatic reduction in the extent of hydrological systems (about 20%), and significant increases of tree canopies in urban areas and near the coastal areas (approximately 76.8%). Paddy fields declined by 51% in 2016; such areas transitioned to inactive status or were alternated for growing drought-tolerant plants. Shrimp farming experienced a recognizable decrease by approximately 44%. The 2014 map and field observations during summer 2016 provide references for object-based classification and validation. Overall agreement of results is about 85%.