Impacts in coastal areas

A rise in average sea level of 10 to 20 cm by 2030 and about up to 1 metre by the end of the next century may not seem a great deal. Many people live sufficiently above the level of high water not to be directly affected. However, half of humanity inhabits the coastal zones around the world.11 Within these, the lowest lying are some of the most fertile and densely populated. To people living in these areas, even half a metre increase in sea level can add enormously to their problems. Their vulnerability is increased by the likelihood of storm surges either due to more intense tropical cyclones or mid latitude storms and by other problems such as local land subsidence and the increased intrusion of salt into groundwater.

Especially vulnerable are large river deltas; in the largest 40 of these in the world over 300 million people live who are increasingly affected by the rate of sea level rise that is occurring even in the absence of climate change (Figure 7.3). Since 1980 over a quarter of a million lives have been lost due to tropical cyclones or storm surges - as I write this paragraph in May 2008, over 100 000 have been lost in a cyclone and storm surge in the Irrawaddy Delta in Myanmar. By 2080, even with only half a metre of sea level rise and no further flood defence, over 100 million in these deltas will be liable to flooding.12 As an example of a delta area I shall first consider Bangladesh; I shall then consider the Netherlands as an example of an area very close to sea level where sea defences are already in place. Thirdly, I shall look at the plight of small low-lying islands in the Pacific and other oceans.

Bangladesh is a densely populated country of about 150 million people located in the complex delta region of the Ganges, Brahmaputra and Meghna Rivers.13 About

Antioquia Bibliatodo
Figure 7.3 Relative vulnerability of coastal deltas as indicated by estimates of the population potentially displaced by current sea level trends to 2050 (extreme, > 1 million; high, 1 million to 50 000; medium, 50 000 to 5000). Climate change would exacerbate these impacts.

Figure 7.4 Land affected in Bangladesh by various amounts of sea level rise. The 1, 2, 3 and 5 m contours are shown.

10% of the country's habitable land (with about 6 million population) would be lost with half a metre of sea level rise and about 20% (with about 15 million population) would be lost with a 1-m rise (Figure 7.4).14 Estimates of the sea level rise are of about 1 m by 2050 (compounded of 70 cm due to subsidence because of land movements and removal of groundwater and 30 cm from the effects of global warming) and nearly 2 m by 2100 (1.2 m due to subsidence and 70 cm from global warming)15 - although there is significant uncertainty in these estimates.

It is quite impractical to consider full protection of the long and complicated coastline of Bangladesh from sea level rise. Its most obvious effect, therefore, is that substantial amounts

Floods help make the cultivable land in Bangladesh fertile and this helps the agriculture sector of the country. But excessive flooding is considered a calamity. The rise in sea water levels, the narrow north tip to the Bay of Bengal, tropical storms that whip up wind speeds of up to 140 mph (225 km h-1) send waves up to 26 feet (8 m tall) crashing into the coast, the shallow sea bed , the fact that water coming down from the Rivers Ganges and Brahmaputra can not escape when the water level rises and the monsoons, all contribute to the severe flooding of the Bangladesh coastline.

Floods help make the cultivable land in Bangladesh fertile and this helps the agriculture sector of the country. But excessive flooding is considered a calamity. The rise in sea water levels, the narrow north tip to the Bay of Bengal, tropical storms that whip up wind speeds of up to 140 mph (225 km h-1) send waves up to 26 feet (8 m tall) crashing into the coast, the shallow sea bed , the fact that water coming down from the Rivers Ganges and Brahmaputra can not escape when the water level rises and the monsoons, all contribute to the severe flooding of the Bangladesh coastline.

of good agricultural land will be lost. This is serious: half the country's economy comes from agriculture and 83% of the nation's population depends on agriculture for its livelihood. Many of these people are at the very edge of subsistence.

But the loss of land is not the only effect of sea level rise. Bangladesh is extremely prone to damage from storm surges. Every year, on average, at least one major cyclone attacks Bangladesh. During the past 25 years there have been two very large disasters with extensive flooding and loss of life. The storm surge in November 1970 is probably the largest of the world's natural disasters in recent times; it is estimated to have claimed the lives of over a quarter of a million people. Well over 100 000 are thought to have lost their lives in a similar storm in April 1991. Even small rises in sea level add to the vulnerability of the region to such storms.

There is a further effect of sea level rise on the productivity of agricultural land; that is, the intrusion of salt water into fresh groundwater resources. At the present time, it is estimated that in some parts of Bangladesh salt water extends seasonally inland over 150 km. With a 1-m rise in sea level, the area affected by saline intrusion could increase substantially although, since it is also likely that climate change will bring increased monsoon rainfall, some of the intrusion of salt water could be alleviated.16

What possible responses can Bangladesh make to these likely future problems? Over the timescale of change that is currently envisaged it can be supposed that the fishing industry can relocate and respond with flexibility to changing fishing areas and changing conditions. It is less easy to see what the population of the affected agricultural areas can do to relocate or to adapt. No significant areas of agricultural land are available elsewhere in Bangladesh to replace that lost to the sea, nor is there anywhere else in Bangladesh where the population of the delta region can easily be located. It is clear that very careful study and management of all aspects of the problem is required. The sediment brought down by the rivers into the delta region is of particular importance. The amount of sediment and how it is used can have a large effect on the level of the land affected by sea level rise. Careful management is therefore required upstream as well as in the delta itself; groundwater and sea defences must also be managed carefully if some alleviation of the effects of sea level rise is to be achieved.

A similar situation exists in the Nile Delta region of Egypt. The likely rise in sea level this century is made up from local subsidence and global warming in much the same way as for Bangladesh - approximately 1 m by 2050 and 2 m by 2100. About 12% of the country's arable land with a population of over 7 million people would be affected by a 1-m rise of sea level.17 Some protection from the sea is afforded by the extensive sand dunes but only up to half a metre or so of sea level rise.18

Many other examples of vulnerable delta regions, especially in Southeast Asia and Africa, can be given where the problems would be similar to those in Bangladesh and in Egypt. For instance, several large and low-lying alluvial plains are distributed along the eastern coastline of China. A sea level rise of just half a metre would inundate an area of about 40 000 km2 (about the area of the Netherlands)19 where over 30 million people currently live. A particular delta that has been extensively studied is that of the Mississippi in North America. These studies underline the point that human activities and industry are already exacerbating the potential problems of sea level rise due to global warming. Because of river management little sediment is delivered by the river to the delta to counter the subsidence occurring because of long-term movements of the Earth's crust. Also, the building of canals and dykes has inhibited the input of sediments from the ocean.20 Studies of this kind emphasise the importance of careful management of all activities influencing such regions, and the necessity of making maximum use of natural processes in ensuring their continued viability.

In September 2008 a report by the government-appointed Delta Commission concluded that the Netherlands must spend billions of euros on dyke upgrades and coastal expansion to avoid the ravages of rising sea levels due to global warming over the coming decades

We now turn to the Netherlands, a country more than half of which consists of coastal lowlands, mainly below present sea level. It is one of the most densely populated areas in the world; 8 million of the 14 million inhabitants of the region live in large cities such as Rotterdam, The Hague and Amsterdam. An elaborate system of about 400 km of dykes and coastal dunes, built up over many years, protects it from the sea. Recent methods of protection, rather than creating solid bulwarks, make use of the effects of various forces (tides, currents, waves, wind and gravity) on the sands and sediments so as to create a stable barrier against the sea - similar policies are advocated for the protection of the Norfolk coast in eastern England.21 Protection against sea level rise next century will require no new technology. Dykes and sand dunes will need to be raised; additional pumping will also be necessary to combat the incursion of salt water into freshwater aquifers. It is estimated22 that an expenditure of about $US12 000 million would be required for protection against a sea level rise of 1 m.

The third type of area of especial vulnerability is the low-lying small island.23 Half a million people live in archipelagos of small islands and coral atolls, such as the Maldives in the Indian Ocean, consisting of 1190 individual islands, and the Marshall Islands in the Pacific, which lie almost entirely within 3 m of sea level. Half a metre or more of sea level rise would reduce their areas substantially - some would have to be abandoned - and remove up to 50% of their groundwater. The cost of protection from the sea is far beyond the resources of these islands' populations. For coral atolls, rise in sea level at a rate of up to about half a metre per century can be matched by coral growth, providing that growth is not disturbed by human interference and providing also that the growth is not inhibited by a rise in the maximum sea temperature exceeding about 1-2 °C.23

These are some examples of areas particularly vulnerable to sea level rise. Many other areas in the world will be affected in similar, although perhaps less dramatic, ways. Many of the world's cities are close to sea level and are being increasingly affected by subsidence because of the withdrawal of groundwater. The rise of sea level due to global warming will add to this problem. There is no technical difficulty for most cities in taking care of these problems, but the cost of doing so must be included when calculating the overall impact of global warming.

So far, in considering the impact of sea level rise, places of dense population where there is a large effect on people have been considered. There are also areas of importance where few people live. The world's wetlands and mangrove swamps currently occupy an area of about 1 million square kilometres (the figure is not known very precisely), equal approximately to twice the area of France. They contain much biodiversity and their biological productivity equals or exceeds that of any other natural or agricultural system. Over two-thirds of the fish caught for human consumption, as well as many birds and animals, depend on coastal marshes and swamps for part of their life cycles, so they are vital to the total world ecology. Such areas can adjust to slow levels of sea level rise, but there is no evidence that they could keep pace with a rate of rise of greater than about 2 mm per year - 20 cm per century. What will tend to occur, therefore, is that the area of wetlands will extend inland, sometimes with a loss of good agricultural land. However, because in many places such extension will be inhibited by the presence of flood embankments and other human constructions, erosion of the seaward boundaries of the wetlands will lead more usually to a loss of wetland area. Because of a variety of human activities (such as shoreline protection, blocking of sediment sources, land reclamation, aquaculture development and oil, gas and water extraction), coastal wetlands are currently being lost at a rate of 0.5-1.5% per year. Sea level rise because of climate change would further exacerbate this loss.25

To summarise the impact of the half metre or more of sea level rise due to global warming which could occur during the twenty-first century: global warming is not the only reason for sea level rise but it is likely to exacerbate the impacts of other environmental problems. Careful management of human activities in the affected areas can do a lot to alleviate the likely effects, but substantial adverse impacts will remain. In delta regions, which are particularly vulnerable, sea level rise will lead to substantial loss of agricultural land and salt intrusion into freshwater resources. In Bangladesh, for instance, over 10 million people are likely to be affected by such loss. A further problem in Bangladesh and other low-lying tropical areas will be the increased intensity and frequency of disasters because of storm surges. Each year, the number of people worldwide experiencing flooding because of storm surges is estimated now at about 40 million. With a 40-cm sea level rise by the 2080s this number is estimated to quadruple - a number that might be reduced by half if coastal protection is enhanced in proportion to gross domestic product (GDP) growth.26 Low-lying small islands will also suffer loss of land and freshwater supplies. Countries like the Netherlands and many cities in coastal regions will have to spend substantial sums on protection against the sea. Significant amounts of land will also be lost near the important wetland areas of the world. Attempts to put costs against these impacts, in both money and human terms, will be considered later in the chapter.

In this section we have considered the impacts of sea level rise for the twenty-first century. Because, as we have seen, the ocean takes centuries to adjust to an increase in surface temperature, the longer-term impacts of sea level rise also need to be emphasised. Even if the concentrations of greenhouse gases in the atmosphere were stabilised so that anthropogenic climate change is halted, the sea level will continue to rise for many centuries as the whole ocean adjusts to the new climate.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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  • Rita
    What are the problems associated with global warming in the coastal area?
    2 months ago
  • daniella
    What are the problems associated with global warming in the coastal areas ?
    2 months ago

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