Impacts of natural and human drivers on the multi-decadal morphological evolution of tidally-influenced deltas

The world's deltas are at risk of being drowned due to rising relative sea levels as a result of climate change, decreasing supplies of fluvial sediment, and human responses to these changes. This paper analyses how delta morphology evolves over multi-decadal timescales under environmental change using a process-based model. Model simulations over 10^2 years are used to explore the influence of three key classes of environmental change, both individually and in combination: (i) varying combinations of fluvial water and sediment discharges; (ii) varying rates of relative sea-level rise; and (iii) selected human interventions within the delta, comprising polder-dykes and cross-dams. The results indicate that tidal asymmetry and rate of sediment supply together affect residual flows and delta morphodynamics (indicated by sub-aerial delta area, rates of progradation and aggradation). When individual drivers of change act in combination, delta building processes such as the distribution of sediment flux, aggradation, and progradation are disrupted by the presence of isolated polder-dykes or cross-dams. This suggests that such interventions, unless undertaken at a very large scale, can lead to unsustainable delta building processes. Our findings can inform management choices in real-world tidally-influenced deltas, while the methodology can provide insights into other dynamic morphological systems

An Integrated Approach Providing Scientific and Policy-Relevant Insights for South-West Bangladesh

Bangladesh is identified as an impact hotspot for sea-level rise in multiple studies. However, a range of other factors must be considered including catchment management, socio-economic development and governance quality, as well as delta plain biophysical processes. Taking an integrated assessment approach highlights that to 2050 future changes are more sensitive to human choice/policy intervention than climate change, ecosystem services diminish as a proportion of the economy with time, continuing historic trends and significant poverty persists for some households. Hence under favourable policy decisions, development could transform Bangladesh by 2050 making it less vulnerable to longer-term climate change and subsidence. Beyond 2050, the threats of climate change are much larger, requiring strategic adaptation responses and policy changes that must be initiated now

The ability of societies to adapt to twenty-first-century sea-level rise

Against the background of potentially substantial sea-level rise, one important question is to what extent are coastal societies able to adapt? This question is often answered in the negative by referring to sinking islands and submerged megacities. Although these risks are real, the picture is incomplete because it lacks consideration of adaptation. This Perspective explores societies' abilities to adapt to twenty-first-century sea-level rise by integrating perspectives from coastal engineering, economics, finance and social sciences, and provides a comparative analysis of a set of cases that vary in terms of technological limits, economic and financial barriers to adaptation and social conflicts

Hydrologic and hydrodynamic modelling of extreme flood events to assess the impact of climate change in a large basin with limited data

Rasul, M ORCiD: 0000-0001-8159-1321The Chartered Institution of Water and Environmental Management (CIWEM) and John Wiley & Sons Ltd. Flood modelling of a large basin like the Fitzroy is a difficult task due to its large catchment size, the long duration of flood events, the non-uniform spatial distribution of rainfall and a lack of required data for modelling purposes. This paper presents a systematic methodology for the flood modelling of the Fitzroy Basin using hydrologic and hydrodynamic modelling approach with Geographic Information System (GIS) capabilities. This study developed five flood scenarios analysing historical flood events and considering three impacts of climate change: upstream subcatchments flooding, local rainfall fluctuations and sea level rise. A hydrologic model was developed within the wider Fitzroy Basin with the five upstream subcatchments and the upper Fitzroy subcatchment in order to simulate discharge data for these scenarios at the Gap measurement location. An integrated hydrologic-hydrodynamic model was developed for the lower Fitzroy subcatchment where output discharges of the hydrologic model were considered as the upstream boundaries. The peak flood levels, peak flow rates and flood inundation durations at Rockhampton city were identified using this integrated model. GIS capabilities were specially used for automatic watershed delineation and river cross-section extraction from Digital Elevation Model (DEM) data. The methodology proposed here is a case study and can be applied to other similar basins or catchments. © 201

Hydrologic and hydrodynamic modelling of extreme flood events to assess the impact of climate change in a large basin with limited data

The Chartered Institution of Water and Environmental Management (CIWEM) and John Wiley & Sons Ltd. Flood modelling of a large basin like the Fitzroy is a difficult task due to its large catchment size, the long duration of flood events, the non-uniform spatial distribution of rainfall and a lack of required data for modelling purposes. This paper presents a systematic methodology for the flood modelling of the Fitzroy Basin using hydrologic and hydrodynamic modelling approach with Geographic Information System (GIS) capabilities. This study developed five flood scenarios analysing historical flood events and considering three impacts of climate change: upstream subcatchments flooding, local rainfall fluctuations and sea level rise. A hydrologic model was developed within the wider Fitzroy Basin with the five upstream subcatchments and the upper Fitzroy subcatchment in order to simulate discharge data for these scenarios at the Gap measurement location. An integrated hydrologic-hydrodynamic model was developed for the lower Fitzroy subcatchment where output discharges of the hydrologic model were considered as the upstream boundaries. The peak flood levels, peak flow rates and flood inundation durations at Rockhampton city were identified using this integrated model. GIS capabilities were specially used for automatic watershed delineation and river cross-section extraction from Digital Elevation Model (DEM) data. The methodology proposed here is a case study and can be applied to other similar basins or catchments. © 201

Ecosystem services linked to livelihoods and well-being in the Ganges-Brahmaputra-Meghna delta

Deltas are dynamic and the relationships between ecosystem services, livelihoods and well-being within them are multi-scalar and often non-linear. Social mechanisms of access and management vary between different bundles of ecosystem services: a social-ecological system approach therefore identifies the trade-offs and interactions which occur across diverse temporal and spatial scales and communities. Although Bangladesh is moving towards a more urbanised future, access to ecosystem services continues to be critical to the well-being of populations in rural areas. However, rights to those services are available to a diminishing few. Current winners and losers from development processes are persistent, and ecosystem services are unlikely to lift the rural poor out of poverty without a complete restructuring of social and economic relations in rural areas

A sustainable future supply of sediment for the Ganges-Brahmaputra delta?

Recent research highlights that delta submergence is an important issue for the Ganges-Brahmaputra-Meghna (GBM) delta. The only factor that could potentially offset losses in delta surface elevation is a sustainable supply of fluvial sediment. River sediments therefore have considerable economic and social value for ecosystem services and those they support. Analysis, using the HydroTrend model, indicates that an increase in the climate-driven supply of fluvial sediment to the GBM delta has the potential, through accelerated aggradation on the delta surface, to offset some of the adverse impacts of climate change due to rising sea levels in the Bay of Bengal. However, anthropogenic disconnections, such as dams, flood defences and polders disturbances, have the possibility to negatively affect this process

Integrative analysis for the Ganges-Brahmaputra-Meghna delta, Bangladesh

The Ganges-Brahmaputra-Meghna delta in Bangladesh is one of the world’s most dynamic deltas and supports high population densities based on large provisioning ecosystem services. Analysing the future of these ecosystem services and associated human livelihoods represents a complex multi-scale, multi-disciplinary problem. A conceptual framework aims to identify mechanisms that link physical processes (including climate change) with ecosystem services and social outcomes providing a shared basis for other analysis, including the design of an integrated model. This also allows the characteristics of co-production of ecosystem services at the landscape scale and significant trade-offs between types of ecosystem services to be incorporated. Adopting a systems-based approach of this scale is challenging but essential to support the effective management of coastal Bangladesh