IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

10.6 Case studies

10.6.1 Megadeltas in Asia

There are 11 megadeltas with an area greater than 10,000 km2 (Table 10.10) in the coastal zone of Asia that are continuously being formed by rivers originating from the Tibetan Plateau (Milliman and Meade, 1983; Penland and Kulp, 2005) These megadeltas are vital to Asia because these are home to millions of people, especially the seven megacities that are located in these deltas (Nicholls, 1995; Woodroffe et al., 2006). The megadeltas, particularly the Zhujiang delta, Changjiang delta and Huanghe delta, are also economically important, accounting for a substantial proportion of China’s total GDP (Niou, 2002; She, 2004). Ecologically, the Asian megadeltas are critical diverse ecosystems of unique assemblages of plants and animals located in different climatic regions (IUCN, 2003b; ACIA, 2005; Macintosh, 2005; Sanlaville and Prieur, 2005). However, the megadeltas of Asia are vulnerable to climate change and sea-level rise that could increase the frequency and level of inundation of megadeltas due to storm surges and floods from river drainage (Nicholls, 2004; Woodroffe et al., 2006) putting communities, biodiversity and infrastructure at risk of being damaged. This impact could be more pronounced in megacities located in megadeltas where natural ground subsidence is enhanced by human activities, such as in Bangkok in the Chao Phraya delta, Shanghai in the Changjiang delta, Tianjin in the old Huanghe delta (Nguyen et al., 2000; Li et al., 2004a; Jiang, 2005; Li et al., 2005; Woodroffe et al., 2006). Climate change together with human activities could also enhance erosion that has, for example, caused the Lena delta to retreat at a rate of 3.6 to 4.5 m/yr (Leont’yev, 2004) and has affected the progradation and retreat of megadeltas fed by rivers originating from the Tibetan Plateau (Li et al., 2004b; Thanh et al., 2004; Shi et al., 2005; Woodroffe et al., 2006). The adverse impacts of salt-water intrusion on water supply in the Changjiang delta and Zhujiang delta, mangrove forests, agriculture production and freshwater fish catch, resulting in a loss of US$125x106 per annum in the Indus delta could also be aggravated by climate change (IUCN, 2003a, b; Shen et al., 2003; Huang and Zhang, 2004).

Externally, the sediment supplies to many megadeltas have been reduced by the construction of dams and there are plans for many more dams in the 21st century (Chapter 6, Box 6.3; Woodroffe et al., 2006). Reduction of sediment supplies make these systems much more vulnerable to climate change and sea-level rise. When considering all the non-climate pressures, there is very high confidence that the group of populated Asian megadeltas is highly threatened by climate change and responding to this threat will present important challenges (see also Chapter 6, Box 6.3). The sustainability of megadeltas in Asia in a warmer climate will rest heavily on policies and programmes that promote integrated and co-ordinated development of the megadeltas and upstream areas, balanced use and development of megadeltas for conservation and production goals, and comprehensive protection against erosion from river flow anomalies and sea-water actions that combines structural with human and institutional capability building measures (Du and Zhang, 2000; Inam et al., 2003; Li et al., 2004b; Thanh et al., 2004; Saito, 2005; Wolanski, 2007; Woodroffe et al., 2006).

Table 10.10. Megadeltas of Asia.

Features  Lena  Huanghe-  Changjiang  Zhujiang  Red River  Mekong  Chao  Irrawaddy  Ganges-  Indus  Shatt-el-Arab  
   Huaihe          Phraya    Brahmaputra    (Arvand Rud)  
Area (103 km243.6 36.3 66.9 10 16 62.5 18 20.6 100 29.5 18.5 
Water discharge (109 m3/yr) 520 33.3 905 326 120 470 30 430 1330 185 46 
Sediment load (10t/yr) 18 849 433 76 130 160 11 260 1969 400 100 
Delta growth (km2/yr) -- 21.0 16.0 11.0 3.6 1.2   10.0 5.5 to 16.0  PD30   
Climate zone Boreal Temperate Sub-tropical Sub-tropical Tropical Tropical Tropical Tropical Tropical Semi-arid Arid 
Mangroves (103 km2None None None None   5.2 2.4 4.2 10 1.6 None 
Population (106) in 2000 0.000079 24.9 (00) 76 (03) 42.3 (03) 13.3 15.6 11.5 10.6 130 3.0 0.4 
Population increase by 2015 None 18 -  176 21 21 44 15 28 45 -- 
GDP (US$109  58.8 (00) 274.4 (03) 240.8 (03) 9.2 (04) 7.8 (04) -- -- -- -- -- 
Megacity None Tianjin Shanghai Guangzhou -- -- Bangkok -- Dhaka Karachi -- 
Ground subsidence (m) None 2.6 to 2.8 2.0 to 2.6 XX -- 0.2 to 1.6 -- 0.6 to 1.9 mm/a   -- 
SLR (cm) in 2050 10 to 90 (2100) 70 to 90 50 to 70 40 to 60 -- -- -- -- -- 20 to 50 -- 
Salt-water intrusion (km) -- -- 100 -- 30 to 50 60 to 70 -- -- 100 80 -- 
Natural hazards -- FD CS, SWI, FD CS, FD, SWI CS, FD, SWI SWI -- -- CS, FD, SWI CS, SWI -- 
Area inundated by SLR (103 km2). Figure in brackets indicates amount SLR. -- 21.3 (0.3m) 54.5 (0.3m) 5.5 (0.3m) 5 (1m) 20 (1m) -- -- -- -- -- 
Coastal protection  No protection Protected Protected Protected Protected Protected Protected Protected Protected Partial Protection Partial protection 

PD: Progradation of coast; CS: Tropical cyclone and storm surge; FD: Flooding; SLR: Sea-level rise; SWI: Salt water intrusion; DG: Delta growth in area; XX: Strong ground subsidence; X: Slight ground subsidence; --: No data available