Long-term quantification of pre and post-monsoon surface water area of Bangladesh

Since the 1990s, about 70 percent of the world's wetland ecosystem have been lost, despite the acknowledged contribution of surface waters to human well-being. Surface water is a prerequisite for agriculture, fisheries, and other human activities. It also significantly impacts the groundwater reserve, soil conditions, the environment, and the surrounding area's ecology. Bangladesh's population and economic expansion have increased the need for water resources. Therefore, monitoring the spatial and temporal distribution of surface water resources is essential. The present study used more than 2700 Landsat scenes from 1990 to 2020 to quantify the total surface water area utilizing the strength of cloud computing in the Google Earth Engine platform. MannKendall trend analysis was performed to understand the trend of the surface water area. In 1990 the total pre-monsoon and post-monsoon surface water areas were 7994.91 km2 and 11453.43 km2 which is 5.38% and 7.71% of the total countries area, respectively. In 2010 and 2020, the water area was 10748.61 km2 (7.24%) and 10313.49 km2 (6.94%), respectively, in the pre-monsoon; and 10794.05 km2 (7.27%) and 15570.36 km2 (10.48%) respectively in the postmonsoon season. The overall change between 2020 and 1990 is 7994.91 km2 (1.89%) in the premonsoon season and 4116.93 (2.77%) in the post-monsoon season. The maximum average surface water area in the post-monsoon season was found in Sylhet (22.68%), followed by Khulna (14.52%). Rangpur was found to have the least average surface water area in both seasons (2.85% and 3.57%). Coastal regions showed a significant increasing trend in the surface water area in the pre-monsoon and post-monsoon seasons. These findings have significant implications for sustainable surface water management decisions, priority interventions, legal frameworks, and public policies to conserve valuable surface water resources in Bangladesh.