Both urban disasters and environmental hot spots are already located disproportionately in low-lying coastal areas. Climate change will increase the risk of both. In particular, rising sea levels will increase the risk of floods, and stronger tropical storms may further increase the flood risk. Low-income groups living on flood plains are especially vulnerable.
Given the long lead times required for climate change mitigation, this will be insufficient to prevent these risks from increasing. Moreover, most other measures, such as encouraging urban development in more environmentally suitable locations, or adapting coastal settlements to reduce their vulnerability, also have long lead times. The scale and nature of the risks need to be better understood in order to motivate and target timely measures. Much of the relevant information is local. However, given the global nature of climate change, it is also important to assess the international dimensions of the coastal risks it is already beginning to pose.
Human settlement has long been drawn to coastal areas, which provide many resources and trading opportunities but also expose residents to various hazards. Historically, the attraction of coasts has been particularly strong among trading nations and empires. In Indonesia, for example, the Mataram Empire, which relied on tribute from rice farmers, favoured inland cities and monuments, while the Sri Vijaya Empire, which relied on controlling trade, favoured coastal cities. Colonialism and the expansion of international trade during the colonial period contributed to the coastal location of many contemporary cities.
The recent expansion of international trade has also contributed to population movements towards the coast. The pre-eminence of ocean shipping has declined, with air freight growing in relative importance. But at least in terms of tonne-kilometres shipped, however, ocean shipping still dominates. Shipping now accounts for less than half of the value of the United States’ merchandise imports and exports but about three-quarters of the weight. In other countries the decline in shipping is far less evident – for Japan the corresponding figures rise to almost three-quarters of the value and over 99% of the weight. China’s on-going economic boom is one of the clearest examples of trade-related coastward movement the world has ever seen, although one could argue that government economic policies have been as important as market pressures in causing this movement.
The concentration of populations and economic activities on and near the coast has had serious environmental consequences. Urban systems have radically altered the flows of water, energy and materials, transforming the pre-existing ecosystems. The review of coastal systems undertaken for the Millennium Ecosystem Assessment concluded that coastal ecosystems, both onshore and offshore, are among the most productive in the world, and also among the most threatened by human settlement. It is estimated that about one-third of coastal mangrove forests and one-fifth of coral reefs have already been lost. In many parts of the world, coastal fish populations have declined considerably.
When scientists recently reviewed conditions in 12 harbours of major Asian cities, all but one had exhibited drastic fishery declines (as well as numerous other environmental problems) in recent decades.
Many coastal populations are at risk from flooding – particularly when high tides combine with storm surges and/or high river flows. Between 1994 and 2004, about one-third of the 1,562 flood disasters, half of the 120,000 people killed, and 98% of the 2 million people affected by flood disasters were in Asia, where there are large population agglomerations in the flood plains of major rivers (e.g. Ganges–Brahmaputra, Mekong and Yangtze) and in cyclone-prone coastal regions (e.g. Bay of Bengal, South China Sea, Japan and the Philippines).
Some features of urban development increase the rise of flooding. Water drains more rapidly from built-over land, increasing peak flows and flood risks, particularly if the built drainage system is not adapted accordingly. In many parts of the world, developers have drained wetlands, sometimes reducing malaria prevalence or opening up valuable land for urban development, but also removing a buffer against tidal floods. Particularly in delta regions, land compaction, subsidence due to groundwater withdrawal and reductions in the rate of sediment deposition (due to water regulation) can lead, in effect, to sea-level rise, increasing flood risk (as well as creating various other problems).
While economic activity and urban development often increase the environmental pressures that lead to flooding, low-income settlements, and poor groups within all settlements, tend to be the most vulnerable. On the one hand, affluent settlements and groups are in a better position to take protective measures and to adapt or escape when flooding does occur (as media coverage and research on hurricane Katrina and New Orleans amply demonstrated). On the other hand, the poorest residents of the cities of low-income countries are often forced (implicitly or explicitly) to settle in flood plains or other hazard-prone locations, as they cannot afford more suitable alternatives.
Climate change will increase the risk of flooding, as well as causing other environmental damage in coastal areas. The estimates of global mean sea-level rise in the Special Report on Emissions Scenarios of the Intergovernmental Panel on Climate Change (IPCC) range from 22 centimetres to 34 centimetres, between 1990 and the 2080s. Far faster sea level rise (more than a metre per century) could result from accelerated melting of the Greenland ice sheet or the collapse of the West Antarctic ice sheet, although this is not considered likely during the twenty-first century. It has been estimated that, in the absence of any other changes, a sea-level rise of 38 centimetres would increase five-fold the number of people flooded by storm surges.
The risks to human settlements could be reduced if people and enterprises were encouraged to move away from the coast, or at least from the most risk-prone coastal locations (this would also reduce the pressures human settlements place on coastal ecosystems). But current population movements are in the opposite direction. Given the character of urban development, and that the factors driving coastward movement are still poorly understood, turning these flows around is likely to be slow, costly or both. In particular, there is the danger that ill-considered or politically short-sighted measures to shift population from the coastal areas will impose unnecessary economic costs on key coastal enterprises and fail to provide the basis for viable alternatives inland or in more appropriate coastal locations. More appropriate measures are sorely needed, and the earlier the better.
In order to support efficient and equitable means for moving the most vulnerable urban settlements, a better understanding is needed of why (and in some cases whether) urban settlements in coastal areas are growing more rapidly than inland. Avoiding policies that favour coastal development (such as the special economic zones in China, whose rapid population growth is described below), and imposing more effective coastal zone management, could make a difference in the longer term. Relatively small shifts in settlement location, out of a coastal plain onto more elevated ground, can make a major difference. However, experience after the Indian Ocean tsunami of 2004, in which over 200,000 people lost their lives and millions more their homes, has demonstrated the profound difficulties involved in instituting more restrictive coastal settlement policies without further undermining the lives and livelihoods of the most vulnerable residents.
Coastal development can also be encouraged to adapt to the risks of climate change. To date, adaptation motivated by climate change has been minimal. However, measures to reduce exposure to existing weather-related hazards can also serve as means of adapting to climate change. Embedding adaptive measures within the urban infrastructure is again either very costly or very slow. It is likely to be easier if action is taken as new areas are settled, rather than after their infrastructure is in place. It has been suggested that development assistance projects could introduce measures to assist in adaptation to climate change. More generally, there are likely to be important areas of overlap between adaptation to climate change, other forms of disaster preparedness and measures to address local environmental health issues (e.g. improved water, sanitation, waste disposal and drainage systems). Particularly for the urban poor, an equitable resolution of the land issues that drive people to settle on land already susceptible to flooding could make a large difference.
China and Bangladesh
Low elevation coastal zones (LECZ), defined here as land area contiguous with the coastline up to a 10-metre rise elevation, contain some 2% of the world’s land and 10% of its population, based on estimates for 2000. Of the more than 600 million people living in the zone, 360 million are urban. This implies an urbanisation level of 60%, compared to a world urbanisation level of slightly less than 50%.
China is the country with the largest population in the LECZ, and Bangladesh has the third largest population in the LECZ. Moreover, China is one of the more rapidly urbanising countries, with particularly rapid urban growth along the coast, while Bangladesh contains one of the most populous delta regions of the world and already has almost half (46%) of its population in the LECZ. The settlement patterns in both of these countries raise serious concerns about the need for adaptation to climate change to start as soon as possible.
In both Bangladesh and China, the population in the LECZ grew at almost twice the national population growth rate between 1990 and 2000. Moreover, in both countries, the urban populations in the LECZ grew particularly rapidly. Indeed, the urban population growth in China’s LECZ was more than three times the national rate, although the Global Rural-Urban Mapping Project (GRUMP) estimates of China’s urbanisation rate for the period are lower than estimates from the United Nations and the Chinese census estimates.
Thus, even as the seaward risks associated with climate change are increasing, the areas most at risk are experiencing particularly high population growth. Some of this may be due to urbanisation, although in Bangladesh flooding is already a major concern and yet the predominantly rural population of Bangladesh’s LECZ is growing at an even faster rate than the country’s urban average. The movement towards the coast in China is linked to urbanisation, but it is also being driven by the trade-oriented economic strategy, and policies that favour urban development along the coast.
China’s rapid urbanisation and coastward population movements, and the economic liberalization and growth that are driving these demographic trends, date back to the early 1980s. The geographical advantages of coastal development have been enhanced by the creation of special economic zones in coastal locations. It has been estimated that the advantages conferred by geography were about equal to those conferred by preferential policies. By amplifying the advantages of coastal settlement with their special economic zones, China is not only attracting more people to the coast now, but is establishing an urban structure that will continue to attract people to the coast far into the future. Unless something is done, there is the possibility that, as well as the people living in the low elevation coastal zone, China’s economic success will be placed at risk.
Overall, the risks of climate change are clearly far more threatening and intractable for Bangladesh than for China. Only about one-fiftieth of China’s land area is in the LECZ, compared to more than two-fifths of Bangladesh’s land. Nevertheless, China too faces potentially serious threats, the evolution of which depends on policy agendas that do not as yet treat climate change as a serious issue.
Gordon McGranahan is Director of the Human Settlements Group at the International Institute for the Environment and Development (IIED) in London
Deborah Balk is Acting Associate Director of the Institute for Demographic Research at the City University of New York (CUNY) and Associate Professor at Baruch College (CUNY), New York
Bridget Anderson is a Research Associate at the Centre for International Earth Science Information Network (CIESIN) at Columbia University, New York
Homepage photo by yunmeng
This is an edited extract of a report published in Environment and Urbanization. Read the complete and fully-referenced report here