Abstract
Droughts are very common in Bangladesh especially in the northwestern part, due to geographical position, variation in Groundwater table, and the spatial variation in seasonal rainfall pattern. In the present study, three drought indices viz., Vegetation Health Index (VHI), Temperature Vegetation Dryness Index (TVDI), and Shortwave Infrared Dryness Index (VSDI), were calculated utilizing multitemporal Landsat images. Field verification was done for the retrieved parameters needed to calculate the indices i.e., soil moisture content and Land Surface Temperature (LST). Results from various indices were compared to understand the drought pattern in the study area. The VHI revealed that 2014 and 2002 were the most drought-prone year and the drought extent in this region intensified from mild to severe drought. Severe drought was found in northern Lalmonirhat, central Nilphamari, and Thakurgaon, the southern part of Dinajpur, dispersed part of Panchagarh districts and sand bars of the river. It is evident that Thakurgaon, Dinajpur, Gaibandha, and the northern part of Lalmonirhat districts face high agricultural drought risk, Nilphamari, Panchagarh, and Rangpur demonstrate medium risk, and Kurigram district shows slight agricultural drought risk. The drought severity was mainly triggered out due to the decreasing trend of vegetation identified by the Normalized Difference Vegetation Index (NDVI) and also for the climbing trend of LST. In the year 2018, drought mainly prevailed due to the increased amount of LST mainly in the Nilphamari district. Several regions such as dried river channels, sand bars, and uncultivated land show high drought conditions due to lack of moisture in this region and reduce water flow impeded by the upstream dams. As drought has great impacts on agriculture, it is expected that this satellite-based drought assessment will be beneficial to improve the understanding of drought in the northwestern regions of Bangladesh.
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