Abstract
Bengal delta experiences immense seasonality of surface water due to its geographical position. This study aims to explore the extent and seasonality of surface water in the southwestern part of Bangladesh (SWB) where human intervention has been rapidly changing the land use for several decades. This explorative study relied on a total of 312 high-resolution Landsat images from 1972 to 2020 and interviews to present crucial months, seasons, and periods for surface water in SWB. The study uses a valid threshold point ‘0′ for Normalized Difference Water Index (NDWI) to extract water pixels and confirms that the NIR band has better efficacy to separate water pixels. On average, the SWB has faced around 5.5% of surface water between 1972–2001, which increased to 12.8% between 2002 and 2020. Based on the median value, around 6% of surface water was observed in the 1990s, which increased to 16% in the 2010s. The average surface water was detected around 6% and 7% in December and January between 1972 and 2001, which expanded to 18% and 19% between 2002 and 2020, mainly because of human interventions such as mix-cropping. The study strongly suggests considering December and January months for further land use and land class studies which focus on the southwestern part of Bangladesh.
Highlights
Bangladesh is a low-lying coastal country which experiences monsoon inundations almost every year
The present remote sensing study explores the trend, extent, and seasonality of surface water at the southwestern part of Bangladesh based on maximum useable Landsat level-1 reflectance observational data
The study discusses numerous water management projects and frequent natural disasters around southwestern part of Bangladesh (SWB) but does not try to provide concrete evidence that these events might be the source of surface water on the upper reaches of the Bengal delta
Summary
Bangladesh is a low-lying coastal country which experiences monsoon inundations almost every year. Such seasonal inundation is useful for the people of Bangladesh due to its potentiality of bumper rice production and local fish migration. The climate complexity in the southwestern part of Bangladesh (SWB) began with the introduction of construction of ‘polder’—an enclosure system through dikes, developed by Dutch experts, around the entire coastal region with a view to protecting the subdivisions from seasonal saline water intrusion, safeguarding tidal-surge from cyclones, and increasing of rice production during monsoon season under the Flood Control Drainage (FCD) project in. Increased siltation in beels (beel is a lake-like wetland with static water around Ganges-Brahmaputra flood plains, monsoon rainfall and the level of water at beels are positively related), canals, and local rivers, (2)
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