Sediment delivery to sustain the Ganges-Brahmaputra delta under climate change and anthropogenic impacts.

The principal nature-based solution for offsetting relative sea-level rise in the Ganges-Brahmaputra delta is the unabated delivery, dispersal, and deposition of the rivers' ~1 billion-tonne annual sediment load. Recent hydrological transport modeling suggests that strengthening monsoon precipitation in the 21st century could increase this sediment delivery 34-60%; yet other studies demonstrate that sediment could decline 15-80% if planned dams and river diversions are fully implemented. We validate these modeled ranges by developing a comprehensive field-based sediment budget that quantifies the supply of Ganges-Brahmaputra river sediment under varying Holocene climate conditions. Our data reveal natural responses in sediment supply comparable to previously modeled results and suggest that increased sediment delivery may be capable of offsetting accelerated sea-level rise. This prospect for a naturally sustained Ganges-Brahmaputra delta presents possibilities beyond the dystopian future often posed for this system, but the implementation of currently proposed dams and diversions would preclude such opportunities.

Sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses.

The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world's largest deltas. It is currently experiencing high rates of relative sea-level rise of about 5 mm/year, reflecting anthropogenic climate change and land subsidence. This is expected to accelerate further through the 21st Century, so there are concerns that the GBM delta will be progressively submerged. In this context, a core question is: can sedimentation on the delta surface maintain its elevation relative to sea level? This research seeks to answer this question by applying a two-dimensional flow and morphological model which is capable of handling dynamic interactions between the river and floodplain systems and simulating floodplain sedimentation under different flow-sediment regimes and anthropogenic interventions. We find that across a range of flood frequencies and adaptation scenarios (including the natural polder-free state), the retained volume of sediment varies between 22% and 50% of the corresponding sediment input. This translates to average rates of sedimentation on the delta surface of 5.5 mm/yr to 7.5 mm/yr. Hence, under present conditions, sedimentation associated with quasi-natural conditions can exceed current rates of relative sea-level rise and potentially create new land mass. These findings highlight that encouraging quasi-natural conditions through the widespread application of active sediment management measures has the potential to promote more sustainable outcomes for the GBM delta. Practical measures to promote include tidal river management, and appropriate combinations of cross-dams, bandal-like structures, and dredging.

Developing socio-ecological scenarios: A participatory process for engaging stakeholders.

Deltas are experiencing profound demographic, economic and land use changes and human-induced catchment and climate change. Bangladesh exemplifies these difficulties through multiple climate risks including subsidence/sea-level rise, temperature rise, and changing precipitation patterns, as well as changing management of the Ganges and Brahmaputra catchments. There is a growing population and economy driving numerous more local changes, while dense rural population and poverty remain significant. Identifying appropriate policy and planning responses is extremely difficult in these circumstances. This paper adopts a participatory scenario development process incorporating both socio-economic and biophysical elements across multiple scales and sectors as part of an integrated assessment of ecosystem services and livelihoods in coastal Bangladesh. Rather than simply downscale global perspectives, the analysis was driven by a large and diverse stakeholder group who met with the researchers over four years as the assessment was designed, implemented and applied. There were four main stages: (A) establish meta-framework for the analysis; (B) develop qualitative scenarios of key trends; (C) translate these scenarios into quantitative form for the integrated assessment model analysis; and (D) a review of the model results, which raises new stakeholder insights (e.g., preferred adaptation and policy responses) and questions. Step D can be repeated leading to an iterative learning loop cycle, and the process can potentially be ongoing. The strong and structured process of stakeholder engagement gave strong local ownership of the scenarios and the wider process. This process can be generalised for widespread application across socio-ecological systems following the same four-stage approach. It demands sustained engagement with stakeholders and hence needs to be linked to a long-term research process. However, it facilitates a more credible foundation for planning especially where there are multiple interacting factors.

Implications of agricultural land use change to ecosystem services in the Ganges delta.

Ecosystems provide the basis for human civilization and natural capital for green economy and sustainable development. Ecosystem services may range from crops, fish, freshwater to those that are harder to see such as erosion regulation, carbon sequestration, and pest control. Land use changes have been identified as the main sources of coastal and marine pollution in Bangladesh. This paper explores the temporal variation of agricultural land use change and its implications with ecosystem services in the Ganges delta. With time agricultural lands have been decreased and wetlands have been increased at a very high rate mainly due to the growing popularity of saltwater shrimp farming. In a span of 28 years, the agricultural lands have been reduced by approximately 50%, while the wetlands have been increased by over 500%. A large portion (nearly 40%) of the study area is covered by the Sundarbans which remained almost constant which can be attributed to the strict regulatory intervention to preserve the Sundarbans. The settlement & others land use type has also been increased to nearly 5%. There is a gradual uptrend of shrimp and fish production in the study area. The findings suggest that there are significant linkages between agricultural land use change and ecosystem services in the Ganges delta in Bangladesh. The continuous decline of agricultural land (due to salinization) and an increase of wetland have been attributed to the conversion of agricultural land into shrimp farming in the study area. Such land use change requires significant capital, therefore, only investors and wealthier land owners can get the higher profit from the land conversion while the poor people is left with the environmental consequences that affect their long-term lives and livelihood. An environmental management plan is proposed for sustainable land use in the Ganges delta in Bangladesh.