Spatio-temporal controls on salinization within the Ganges Delta, southwest Bangladesh

Human and ecosystem health within Asian deltas are at risk from rising salinity linked to climate change and anthropogenic activities. Southwest Bangladesh is identified as a region at particular risk due to reduced upstream discharge, low elevation and relative sea-level rise. However, a comprehensive and integrated understanding of the spatio-temporal controls on salinity within the delta is currently lacking and provides the focus for this presentation. A large amount of in-situ measurement data from a network of salinity (n = 54) and water level (n = 19) monitoring sites, maintained by Bangladesh Water Development Board, were collated and analyzed. Multiple regression modelling and Seasonal Trend Decomposition of hydro-morphological parameters including elevation, distance from the primary river source, and water levels have been used to constrain temporal trends and determine relative influence on salinity. Results show high salinity (> 5000 mg/L of Total Dissolved Solids) is prevalent in the southwest of Bangladesh, associated with a region of low elevation (< 3m above mean sea level). Lower salinity (< 1000 mg/L) is observed where elevation exceeds 3m, and is consistently < 500 mg/L at elevations > 6m. Inter-annual variation within the southwest is high, with salinity > 12500 mg/L extending up to 120 km inland. Multiple linear regression models show a strong relative influence of increased distance from the primary river source with increased salinity, which also correlates with lower elevation. Tidal water level trends also show a strong spatial distribution pattern, corresponding with three hydro-morphological regions of the delta. Spatial variation in salinity results from complex interactions between geomorphological and hydrological factors. Regional trends in salinization and tidal water levels are identified which are also frequently subject to localized modification of landform/landuse. The identification and quantification of regionally specific primary drivers will help guide adaption strategies and focus mitigation efforts on vulnerable areas.