What does 1.5ºC mean for vulnerable deltas? A study of the Ganges-Brahmaputra-Meghna

16:15 Wednesday 29 May

SS031 • OC185

Room S6


Sally Brown (United Kingdom) 1; Robert J Nicholls (United Kingdom) 2; Attila Lazar (United Kingdom) 2; Duncan D Hornby (United Kingdom) 2; Chris Hill (United Kingdom) 2; Sugata Hazra (India) 3; Kwasi Appeaning Addo (Ghana) 4; Anisul Haque (Bangladesh) 5; John Caesar (United Kingdom) 6; Emma Tompkins (United Kingdom) 2

1 – Bournemouth and Southampton Universities; 2 – University of Southampton; 3 – Jadavpur University; 4 – University of Ghana; 5 – Bangladesh University of Engineering and Technology; 6 – Met Office

Deltas are home to millions of people world-wide, many of whom are exposed to coastal and fluvial flooding today. With approximately 40% of the present delta in the flood plain (taking account of sea-level and surge heights), the Ganges-Brahmaputra is vulnerable to sea-level rise and other drivers of climate change, in a development context.

Using an integrated model (the Delta Dynamic Integrated Emulator Model), the flood depth, area and population affected by sea-level rise was projected in future world’s corresponding with 1.5ºC, 2.0ºC and 3.0ºC with respect to pre-industrial.

Results indicated that annual variability today could be potentially more important than an additional 0.5ºC of warming. Today, land is partially protected against flooding through polders. When comparing the impact of 3.0ºC of warming 1.5ºC of warming, flooding in protected areas (assuming there are no increases in protection standards or other engineered adaptation) is projected to double to between 0.07 and 0.09 m, whilst in unprotected areas, the depth of flooding is projected to increase by approximately 50% to 0.21–0.27m, with the area of land inundated increasing by 2.5 times.

Given the time delay between global mean temperature rise and subsequent warming, sea-levels will continue to increase after 3.0ºC and/or on centennial scales. Under a climate change mitigation at 1.5ºC scenario in 2300, approximately 60% of the delta will be in the flood plain, taking account of a higher water levels due to sea-level rise and under surge conditions. This increases to approximately 90% under a non-mitigation scenario. Taking a similar approach in the Indian Bengal (the western part of the Ganges-Brahmaputra delta), Mahanadi and Volta deltas, indicates similarly large percentages of land are at risk from flooding due to sea-level rise over the centuries. Traditionally, sedimentation during flood events raises land levels, but dam building has reduced sedimentation availability. Levees also reduce sedimentation deposition, meaning that relative sea-level rise is enhanced.

Adapting to sea-level rise brings long-term challenges, balancing and integrating a portfolio of practices in a sustainable way. Adaptation may be best targeted in highly populated parts of the delta (e.g. Khulna and Barisal), or those areas which are particularly important for sustaining livelihoods. Nationally planned adaptation could support autonomous action at a local level, to reduce the impacts of climate change, whilst aligning to wider development goals.