Drought Monitoring in the Coastal Belt of Bangladesh Using Landsat Time Series Satellite Images

Drought is a recurrent phenomenon in Bangladesh but it received very little attention in terms of early warning, detection, preparedness and mitigation of droughts. To manage all these aspects, an effective drought monitoring system is the prime pre-requisite. Till date, scientists worldwide have put several efforts to develop drought mapping and monitoring system using indices, which are derived from meteorological and satellite data. This study presents a method for spatio-temporal monitoring of drought in the coastal region of Bangladesh. Standardized Precipitation Index (SPI), which is based on meteorological data, is used in a GIS environment to generate drought hazard maps in the study area. On the other hand, time series Landsat satellite images were used to calculate various remote sensing based indices such as NDVI, VCI, TCI, VHI and NDWI in order to determine the extent of drought. Each of the indices produced a raster map, which is then reclassified to produce binary images with “drought” and “no-drought” classes. Finally, accuracy assessment of drought detection capability of the indices was done by formulating a comparison matrix from a set of values of randomly generated points within the study area. The result showed that NDVI and VCI are the most reliable indices for drought mapping for the study area based on the SPI values as standard. This study enabled a process of drought mapping basing on remote sensing indices and a comparative assessment of the performance of different indices as well. Inadequate numbers of meteorological stations in Bangladesh as well as missing rainfall data in some of those stations made the calculation of SPI values less accurate. As a consequence, the accuracy level of index based drought identification has been deteriorated. Moreover, lack of ground truth data imposed a drawback on the accuracy assessment process. In spite of the aforementioned shortcomings, the methodology adopted in this study is capable of mapping the spatio-temporal pattern of drought from time series Landsat Satellite images with acceptable accuracy. This study recommends further research on assessing the suitability of all other drought indices for Bangladesh, formulation of drought definition policy and development of integrated drought monitoring system comprising meteorological, statistical, observational and remote sensing data.