10.2.4.2. Coastal Flooding and Inundation

Tokyo, Osaka, and Nagoya are located in the coastal zone, and together they account for more than 50% of Japan's industrial production. In these metropolitan areas, about 860 km² of coastal land-an area supporting 2 million people and with physical assets worth $450 billion (1985 dollars)-already are below mean high-water level. With a 1-m rise in mean sea level, this area would expand by a factor of 2.7 to embrace 4.1 million people and assets worth $908 billion. The same sea-level rise would expand the flood-prone area from 6,270 km² to 8,900 km². The cost of adjusting existing protection measures has been estimated at about $80 billion (IPCC 1996, WG III, Section 6.5.2).

One of the potential threats that sea-level rise poses to the coastal environment is exacerbated beach erosion. Sandy beaches occupy 20-25% of the total length of the Japanese coast. About 120 km² of these beaches have been eroded over the past 70 years. According to Bruun's Rule, an additional 118 km² of beaches-57% of the remaining sandy beaches in Japan today-would disappear with a 30-cm sea-level rise. This percentage would increase to 82% or 90% if the sea level rose by 65 cm or 100 cm, respectively (Mimura, 1995).

Temperate Asia experiences tropical cyclones every year; these storms inundate and exacerbate flood situations in coastal areas, eroding and restructuring coastal formations. There is no conclusive evidence that the frequency or intensity of tropical cyclones would change as a result of climate change or that a systematic shift in their tracks would occur (IPCC 1996, WG II, Section 9.3.2). However, with the projected sea-level rise, even if the frequency and severity of storms remain unchanged in the future, storm surge could still present an increased hazard. It should be pointed out that China and other countries of the region have a long history of experience in the defense against sea encroachment, through the construction of dikes, seawalls, and other structures (ESD-CAS, 1994).

10.2.4.3. Integrated Coastal Zone Management

Coastal oceans provide rich living and nonliving resources; serve as media for transportation and recreation; and receive, dilute, and transform massive quantities of wastes from human activities on land. Coastal oceans already are under stress as a result of a combination of factors (e.g., increased population pressure, habitat destruction, increased land-based pollutant loads, and increased nutrient inputs from rivers). The effects of climate change therefore will constitute additional-largely adverse-series of impacts on an already overstressed resource, with potential for synergistic relationships among stresses (IPCC 1996, WG II, Section 8.2.2).

Coastal oceans provide rich living and nonliving resources; serve as media for transportation and recreation; and receive, dilute, and transform massive quantities of wastes from human activities on land. Coastal oceans already are under stress as a result of a combination of factors (e.g., increased population pressure, habitat destruction, increased land-based pollutant loads, and increased nutrient inputs from rivers). The effects of climate change therefore will constitute additional-largely adverse-series of impacts on an already overstressed resource, with potential for synergistic relationships among stresses (IPCC 1996, WG II, Section 8.2.2).

10.2.5. Human Settlements and Industry

10.2.5.1. Human Settlements

If future climates resemble those projected by GCMs, wetter coasts, drier midcontinent areas, and sea-level rise may cause the gravest effects of climate change through sudden human migration, as millions of people are displaced by shoreline erosion, river and coastal flooding, or severe drought. For example, agricultural settlements in China are projected to be sensitive to drought conditions (IPCC 1996, WG II, Section 12.4.2).

Climate change may affect the intensity or the probability of the occurrence of extreme weather events. The impact of extreme events on human settlements can be affected by the grade of the extreme event, the level of economic and technological development, and the extent of countermeasures taken. In Japan, for example, although the number of deaths is large for the more severe typhoons, such deaths have been declining since World War II (see Figure 10-3). This decline is thought to have occurred because of increasingly effective mitigation measures taken during the past 40 years. These measures include conservation of mountain slopes, rivers, and coasts; harmonization of institutions and laws related to disaster mitigation; preparation of systems for disaster prevention, including better design; meteorological observation and information systems; promotion of people's consciousness with regard to preventing disasters; and development of communication systems for disaster occurrences. On the other hand, economic damages from typhoons have been rising in Japan during the same period because of the increasing values of properties along the coasts (IPCC 1996, WG II, Section 12.4.2).

Figure 10-3: Change in numbers of deaths per typhoon in Japan during the past 70 years. Typhoon grade: I-weak; II-normal; III-strong; IV-stronger; V-violent; VI-super-violent (after IPCC 1996, WG II, Figure 12-2).

In mountain lands and continental permafrost areas, cryospheric change could reduce slope stability and increase the incidence of natural hazards for people, buildings and other structures, pipelines, and communication links (IPCC 1996, WG II, Section 7.5).

During summer days, from the early morning to the time of maximum temperature, the temperature inside a big oasis in the arid regions of northWest China usually is 2-3°C lower than that outside the area; this gradient is called the "oasis effect" (Du and Maki, 1994; Yoshino and Liu, 1997). In the future, as the population increases in oases, so will the cultivated area and water consumption. This pattern could lower the moisture content in the oasis and hence weaken the oasis effect. Climate change thus could compound the hardship for human settlements in the oases.

Ironically, some arid regions of northWest China also have been suffering from heavy rainfall and flood damages. In Xinjiang, during the period 1949-1990, about one-third of the total natural hazards and two-thirds of the total losses incurred by natural hazards were caused by floods (Yoshino and Liu, 1997). Under global warming, this tendency could be intensified because intense rainfall is likely to occur more frequently.

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