Fig. 1

a Surface geo-potential height (contour) in this study. The solid and dashed contour intervals are 1000 and 200 gpm, respectively. Vapor source regions were divided into seven regions: the Pacific Ocean (red), the Bay of Bengal (Yellow), the Arabian Sea (purple), northern part of the Indian Ocean (light blue), southern part of the Indian Ocean (dark blue), land surface (green), and others (black). The dotted line indicates the area of (b). b Locations of the observation sites over Bangladesh. The topographic data (GTOPO30) were downloaded from the United States Geological Survey (USGS)