Climate change projections
This work forms part of a Policy Briefing on Climate Change in Bangladesh produced by Practical Action in 2008. Other sections of the report can be seen in the Related Pages section to the right, where the full report can also be downloaded.
The vast majority of climate change predictions relevant to Bangladesh have been made using regional climate models. These indicate that warming across Asia will accelerate. The rate of warming in the South Asia is projected to be significantly faster than that seen in the 20th century, and more rapid than the global mean rate of warming.
- During December, January and February warming is expected to be at its greatest and associated with a decrease in precipitation, whilst the consensus of regional models is that summer rainfall will increase.
- Extreme weather events are projected to increase in frequency in South Asia, including heatwaves and high rainfall. Tropical cyclone intensity is also expected to rise by 10 - 20% as sea surface temperature rises by 2 - 4°C.
- Glacial and sea-ice melt and the expansion of the oceans with increased temperature mean that a rise in sea level is certain. The minimum change, suggested by the most conservative climate change models, is for a 40cm rise by the end of the century.
The predicted seasonal changes for the South Asia region are summarised here. The changes have been calculated relative to the average temperature and precipitation in the period 1961-1990. Note that the results of climate projections for high and low future global greenhouse gas emissions are presented - demonstrating the enormous difference in the impacts that result from alternative future levels of greenhouse gas emissions, particularly by the end of the century. The figures also demonstrate the impact that the highest emitting countries - the most developed countries in the West - have on South Asia. The 'high emissions' figures assume rapid, fossil fuel-intensive economic growth over the coming century: very much a business as usual in the global economy. The 'low emissions' figures, on the other hand, assume reductions in the use of natural resources and the introduction of clean and resource-efficient technologies during the course of this century. The implication is clear - large cuts in carbon emissions and radical changes in global patterns of consumption, particularly in the West, will be required to prevent climate change from bringing catastrophic changes across South Asia.
Future impacts and vulnerabilities
The IPCC identify South Asia as having the highest proportion of 'highly vulnerable' sectors of all the Asia sub-regions, with food, biodiversity, water, costal ecosystems, human health and land degradation all judged to be 'highly vulnerable' to the impacts of climate change. Bangladesh's National Adaptation Programme of Action (NAPA) provides more detail about the most vulnerable sectors and localities in Bangladesh.
The most profound impacts of climate change in Bangladesh will be in agriculture and food security, costal areas, water, biodiversity and ecosystem changes, and human health.
Agriculture and food security: Overall crop yield (wheat, maize and rice) could decrease in South Asia by up to 30% by the end of this century (compared with an increase of up to 20% in East and South East Asia). In cereal production alone, the most conservative climate change projections suggest a minimum decline across South Asia of between 4 and 10%. In Bangladesh, rice production could fall by 8% and wheat production by 32% as early as 2050. Substantial losses in rain fed wheat are also anticipated - studies in India suggest that a 0.5ï‚°C rise in winter temperature would reduce wheat yield by 0.45 tonnes per hectare. Similarly, a rise in temperature of beyond 2.5ï‚°C would reduce non-irrigated wheat and rice farm revenue by 9-25%. Flood water and saline intrusion will also undermine agricultural productivity in Bangladesh. Global climate change and the increased frequency of ENSO events affect the migration routes and numbers of fish larvae currently present in South Asian waters and as a result a general decline in fishery production is anticipated across the region. Fish stocks of local species are currently reported to be in decline due to early flooding, temperature fluctuations and river bed siltration. However, predicting fish stocks is complex and multiple overlapping factors will all contribute to future availability of fish supply.
Water resources: Glacier melting has a significant impact for much of South Asia. River runoff initially increases during winter or spring but as the ice resource depletes, the supply of water will reduce. Those areas that rely on irrigation for agriculture will be particularly affected. Increasing demand for water from an expanding population, increasing evaporation, and increased sedimentation are all expected in Bangladesh. These effects, combined with decreases in winter precipitation, will lead to an expansion of the areas in water stress. All future emissions scenarios predict increasing water stress, with the effects being felt as early as 2020. Moreover, increasing sedimentation reduces the navigability of rivers which are required for around 30% of freight transport in Bangladesh, increases flood risk and causes the development of charlands (sandbanks).
Flood risk: Existing vulnerability to flooding, caused by upstream deforestation, will be aggravated by the effects of climate change. Climate change is anticipated to bring increased sedimentation and an increase in extreme rainfall events, both of which will increase flood risk beyond its current high levels.
Coastal/ low lying areas: All coastal areas in Asia are currently facing increasing stress with threats to human and environmental resilience. However, rising sea levels will have further, major impact on costal and low lying communities in South Asia. The most conservative climate change scenarios predict a rise in sea level of 40cm by the end of this century, which will increase the annual number of people affected by flooding in Asia from 12 million to 94 million, with almost 60% of these people living in South Asia (including the coastlines of Pakistan, Sri Lanka and Bangladesh). Modelling suggests that 1 million people will be directly affected by sea level rise in 2050 in the region of the Bangladesh Ganges-Brahmaputra-Meghna mega-delta. Moreover, Bangladesh's coastal areas will continue to suffer from saline water intrusion, coastal land degradation, storm surges and drainage congestion due to high water flow and sedimentation in the flood plain.
Ecosystems and biodiversity: Increased salinity/ salt water intrusion is likely to adversely effect the trees of the sunderban, whilst lower river and ground water flows may lead to desertification in some areas of the costal zone. It is estimated that a 45cm rise in sea level would inundate 75% of the sunderban.
Human health and migration: The burden of climate attributable diarrhoea and malnutrition is already high in Bangladesh relative to elsewhere in Asia. Future climate projections suggest that this large relative risk is expected to increase, with flooding and sea level rise causing pollution in surface water and an increase in cholera and diarrhoeal diseases. Increasing temperatures are likely to yield a spread in insect borne diseases, whilst warmer sea-surface temperatures support phytoplankton blooms that are the breading ground for bacterial diseases such as cholera. Climate change is also likely to worsen the present problems of land degradation, food supply, drinking water supply, rural poverty and urban unrest in Bangladesh. Migration following extreme weather events is also to be expected, whilst temporary migration to sell labour is a response currently employed by fisher communities suffering from reduced fish stocks.