Figure 7-2: Confidence ratings for impacts of climate change on human settlements.
What makes resource-dependent settlements unique is the extent to which they are dependent on and tuned to the natural resources of the region and the extent to which they are vulnerable to changes in these natural resources. Resource dependency emphasizes the impact of climate change on the economic livelihood of inhabitants. An extreme form of resource-dependent settlements are settlements of traditional peoples, including hunter-gatherer communities, subsistence agricultural settlements, artisanal fishing communities, and the like. The issues are somewhat different in different locations, as indicated below.
Human societies have been developing by adaptation to the arid environment in desert regions for centuries. An example is the oasis water supply system called karez, qanats, or foggaras. For adaptation or mitigation, windbreaks are a powerful method to reduce the effects of the strong winds, dust storms, and sand dune movements (Du et al., 1996; Maki et al., 1997a,b). In addition, trees in windbreaks provide materials for construction and firewood for people, keep a better hygienic environment in the settlements, and improve conditions for crops and livestock.
Social vulnerabilities in arid regions include low income among residents as a result of underdevelopment of industry in the oases, difficulty in telecommunication and transportation between oases, and growing human pressure on the limited land base, as illustrated by the scarcity of suitable irrigable land in oases in the Taklimakan Desert, northwest China (Yoshino, 1997c, 1998). On the northern rim of the Taklimakan desert, only 4–4.5% of the land is available for irrigation, and only about 2% on the south rim is available. Although these limit values vary from desert to desert because of the amount of available water, scarcity of suitable land is a vulnerable feature of settlements in all arid regions. In northern Africa, southwest Asia, and parts of the Middle East, there is a belt of entire countries that currently suffer from inadequate water supplies (see Chapter 4). Increasing temperatures and reduction in rainfall would further limit these settlements.
Figure 7-2: Confidence ratings for impacts of climate change on human settlements. |
Climate change could reduce water availability in the semi-arid savanna ecosystem of tropical Africa, affecting farmers, herders, and tourist-industry workers, which in turn will impact human settlements. Conflict already occurs between herdsmen and farmers in this region, and the SAR discussed the impacts on major cities when people leave the land (see Chapter 10).
Small settlements in arid/semi-arid regions occasionally confront a higher risk of damage by flooding than their counterparts in more humid environments. This is usually because of the longer return periods or rarity of extreme rainfall. However, in a warmer world the frequency of these intense storms in semi-arid and arid regions may increase (Smith, 1996; Smith and Handmer, 1996; Smith et al., 1999). During extreme rainfall events, houses, roads, irrigation systems, and other constructions are destroyed and human settlements in oases are isolated because telecommunication and traffic connections are broken. Because settlements have been adapted to dry conditions, the total numbers of deaths and the total amount of damages caused by drought and other impacts of dry conditions often are smaller than those caused by heavy rainfall.
There are two major types of polar and subpolar settlements: traditional indigenous communities that are based on hunting and gathering activities such as whaling, caribou hunting, and seal hunting and modern “outpost” settlements such as military, mining, and oil camps. The more traditional settlements are economically vulnerable to changes in the regional ecology that might occur as a result of climate change (changes in sea ice, migration routes, or abundance of game species). Although military and mining operations generally would not be concerned with game species, impacts of warming on permafrost areas, sea lanes, and flying weather could significantly improve or reduce the efficiency of resource extraction (Cohen, 1997). Infrastructure in both types of settlements is vulnerable to permafrost melting, desiccation during warming, landslides, and flooding (see Chapter 16).
Traditional settlements of indigenous peoples still exist in (mostly tropical) portions of Africa, Asia and nearby islands, and Latin America. Although these societies engage in subsistence agriculture and some cash activities such as guiding tourists, much of their economy is based on subsistence hunting and gathering. Already under threat from growth in farming, mining, and commercial forestry activities (which may themselves be affected by climate change), under climate change the traditional forest communities would face the additional challenge of changed ecology, which could change the availability of key species and adversely affect the sustainability of these communities.
Agroindustry is considered to be among the more adaptable industries affected by climate change. Brown and Rosenberg (1996) and Brown et al. (1998) were able to show, for example, that growing switchgrass (Panicum virgatum) for biomass is an effective adaptation in the warmer, drier climates expected in central North America under climate change. Chapter 5 also describes agriculture as adaptable and discusses adaptive responses. However, the capacity to adapt varies significantly among regions and among groups of farmers within regions. Adaptability and sustainability of agriculture and agroindustry depend not only on resources such as favorable climate, water, soils, and amount of land but also on the adaptability of whole market chains, which in turn are influenced by wealth levels, technical and financial sophistication, and institutional flexibility and strength (Tweeten, 1995; Nellis, 1996).
Changes in ocean conditions from El Niño episodes have demonstrated that changes such as ocean warming have substantial impacts on the locations and types of marine species available (UNEP, 1989; Meltzoff et al., 1997; Suman, 2001). Fishery-based settlements would be strongly affected as fishermen follow high-valued stocks to other locations, make do with lower valued stocks, or even abandon fishing altogether (see Chapters 6, 10, 14, 15, and 17). Other communities may benefit if high-valued stocks become more accessible.
What often is not appreciated about resource-dependent settlements is the complexity of the economic and social relationships among participants. Changes in the technology of farming, transportation, and communications have integrated farming communities into national and world markets as never before and increasingly have made farming a part-time activity in some parts of the developed world (e.g., Sakamoto, 1996; Sasaki, 1996) and the developing world. The complexity of interactions and the increasing degree of integration offer additional means of adaptation to climate change at the regional level, but these factors also mean that agriculture and agroindustry are being challenged from several directions at once, possibly complicating the impact of climate change alone (see, for example, Chapter 10).
To illustrate some of the complexities involved, in Japan agrarian structures have changed drastically during the past 30 years (Kumagai, 1996). Small farms have evolved through cooperative groups facing environmental requirements, double-cropping, cheaper imports, and high national economic growth (Sakamoto, 1996) into a regional system of farm households, hamlets, traditional villages, villages, and towns (Yoshino, 1997a,b), with significant part-time labor (Sasaki, 1996), and economics of large-scale production in farming, reductions in investment risks costs, diversification within farming, diversification between farming and other activities, and increases in nonfarm income.
Japanese rice-growing illustrates some constraints on adaptation and community sustainability. Inefficient agriculture (ironically) ties the younger generation to the rural community, where they play important roles in making the community active and viable. Provision of modern facilities and infrastructure does not lead to sustainable communities; more important, one must consider residents’ pride or attachment to the community. Realization of a sustainable community requires investments in time, talent, and money for the future of the community (Tabayashi, 1996). Autonomous adaptation here, as elsewhere, might involve numerous social and economic dimensions that involve the entire settlement. It is unlikely to be simple or straightforward and may not result in sustaining every settlement.
The SAR noted that tourism—a major and growing industry in many regions—will be affected by changes in precipitation patterns, severely affecting income-generating activities (IPCC, 1998). The outcome in any particular area depends in part on whether the tourist activity is summer- or winter-oriented and, for the latter, the elevation of the area and the impact of climate on alternative activities and destinations. For example, in spring 1997, when conditions in alternative destinations in the Alps were poor, the number of skiers in the High Atlas in Morrocco increased (Parish and Funnell, 1999). Scotland has been predicted to have less snow cover at its lower elevation ski areas with global warming but may have drier and warmer summers for hill-walking and other summer activities (Harrison et al., 1999) (see regional chapters for other examples).
The impacts of sea-level rise on coastal tourism are compounded by the fact that tourist facility development planning and execution in many cases has been inadequate even for current conditions, leading to environmental problems such as water shortages (Wong, 1998). Furthermore, tourism businesses, which usually are location-specific, have a lower potential than tourists themselves (who have a wide variety of options) to adapt to climate change (Wall, 1998). Small island states may find themselves especially vulnerable to changes in the tourism economy because of their often high economic dependence on tourism, concentration of assets and infrastructure in the coastal zone, and often poor resident population (see Chapter 17).
Whetton et al. (1996) quantified the effects of climate change on snow cover in the Australian Alps, which illustrates the problems of snow-based recreation activities. Under the best-case scenario for 2030, simulated average snow-cover duration and the frequency of more than 60 days cover annually decline at all sites considered. However, this effect is not very marked at higher sites (above 1,700 m). For the worst-case scenario, at higher sites, simulated average snow cover roughly halves by 2030 and approaches zero by 2070. At lower sites, near-zero average values are simulated by 2030.
Riverine and coastal settlements are notable largely for the potential that flooding and especially sea-level rise can have on them; steeplands in many regions are expected to become more vulnerable to landslides. The mechanisms of these effects depend on the settlement being located in harm’s way. River floods can arise from intense local rainfall events or rapid snowmelt, for which long-term probabilities are difficult to forecast (see Chapter 4; Georgakakos et al., 1998). Rapid snowmelt from rain-on-snow events or warm periods in the middle of winter is a potential threat in a warmer world in some heavily settled, snow-fed river systems such as the Rhine in Europe (see Chapter 13), whereas steeplands may suffer more landslides and snow avalanches (e.g., Evans and Clague, 1997). The mechanisms of adaptation are similar: defend against flooding or landslides with increasingly expensive protection structures; retreat from the floodplain and unstable areas to safe ground; or accommodate flooding and landslides in structure design, land-use planning, and evacuation plans (see also Chapters 9, 10, 11, 12, 13, 15, and 17).
The most widespread serious potential impact of climate change on human settlements is believed to be flooding. A growing literature suggests that a very wide variety of settlements in nearly every climate zone may be affected, although specific evidence is still very limited. Riverine and coastal settlements are believed to be particularly at risk, but urban flooding could be a problem anywhere storm drains, water supply, and waste management systems are not designed with enough system capacity or sophistication to avoid being overwhelmed. Urbanization itself explains much of the increase in runoff relative to precipitation in settled areas (Changnon and Demissie, 1996) and contributes to flood-prone situations.
In coastal regions (especially on river deltas and small islands), sea-level rise will be the most fundamental challenge of global warming that human settlements face. Some additional national and regional analyses of coastal vulnerability to sea-level rise have been published since the SAR. Many of these studies are summarized in Chapters 6 and 8 because of the importance of the issue to these sectors. In general, estimates of potential damages continue to increase because of increased movement of people and property into the coastal zone, even though the expected degree of sea-level rise has decreased. Worldwide, depending on the degree of adaptive response, the number of people at risk from annual flooding as a result of a 40-cm sea-level rise and population increase in the coastal zone is expected to increase from today’s level of 10 million to 22–29 million by the 2020s, 50–80 million by 2050s, and 88–241 million by the 2080s (Nicholls et al., 1999). Without sea-level rise, the numbers were projected at 22–23 million in the 2020s, 27–32 million in the 2050s, and 13–36 million in the 2080s. The 40-cm sea-level rise is consistent with the middle of the range currently being projected for 2100 by Working Group I. In 2050, more than 70% (90% by the 2080s) of people in settlements that potentially would be flooded by sea-level rise are likely to be located in a few regions: west Africa, east Africa, the southern Mediterranean, south Asia, and southeast Asia. In terms of relative increase, however, some of the biggest impacts are in the small island states (Nicholls et al., 1999).
Although a 1-m sea-level rise is not considered likely before 2100, it often is used to calibrate many damage estimates. For example, a macroscopic analysis of coastal vulnerability, areas, population, and amount of assets at risk from sea-level rise and storm surges for Japan shows about 861 km2 of land currently is below the high-water level, with 2 million people and 54 trillion Japanese yen in assets. A 1-m sea-level rise would expand the area at risk 2.7 times, to 2,339 km2, and increase population and assets at risk to 4.1 million and 109 trillion Japanese yen, respectively (Mimura et al., 1998). El-Raey (1997) identifies potential impacts on Egypt: 2 million persons and 214,000 jobs affected, US$35 billion in land value, property, and tourism income lost for a 50-cm sea-level rise. For a 100-cm rise, Zeidler (1997) identifies potential land losses of US$30 billion, plus US$18 billion at risk of flooding and as much as US$6 billion of “full protection” in Poland. (See also Nicholls et al., 1999, for potential damages to settlements on the world’s coasts; Adger, 1999, specifically for damages to human settlements in Vietnam; Weerakkody, 1997, for Sri Lanka; and Liu, 1997, for China.)
If sea-level changes occur slowly, economically rational decisions could be made to protect only property that is worth more than its protection costs. With foresight, settlements can be planned to avoid much of the potential cost of protection, given that between 50 and 100 years are expected to pass before a 1-m sea-level rise would be expected. Yohe and Neumann (1997) offer a method by which this planning might be applied. This method can reduce the costs of protection by more than an order of magnitude. Yohe et al. (1996) estimate discounted (at 3% yr-1) cumulative U.S. national protection costs plus property abandonment costs for a 1-m sea-level rise by the end of the 21st century at US$5–6 billion, as opposed to previous estimates of $73–111 billion (Smith and Tirpak, 1989). Sea-level rise exacerbates beach erosion, changes sedimentation patterns, increases river floors in estaurine zones, and inundates wetlands and tidal flats. Groundwater salinization also is a serious problem in coastal zones and many small islands, where recharge does not keep up with usage even under current conditions (Liu, 1997). Higher sea levels are projected to further reduce the size of coastal fresh aquifers and exacerbate the problem. Directly, it causes drinking water quality problems for people in settlements; indirectly, it may limit agriculture in coastal zones (e.g., Dakar, Senegal—Timmerman and White, 1997). Groundwater pumping makes matters worse in many coastal zones by contributing to serious land subsidence. Examples of human settlements affected range from modern European cities (Venice) to large coastal settlements in developing countries (Alexandria, Tianjin, Jakarta, and Bangkok) (Timmerman and White, 1997; Nicholls et al., 1999).
Vulnerabilities of settlements in coastal regions to higher sea levels are compounded by severe wind damage and storm surge caused by tropical cyclones and extra-tropical cyclones. The possibility of increasingly frequent (in some regions) or more intense tropical cyclones also cannot be rejected (see Chapter 3). Even if cyclones do not increase in intensity or frequency, with sea-level rise they would be expected to be an increasingly severe problem in low-lying coastal regions (e.g., for settlements along the North Sea coast in northwest Europe, the Seychelles, parts of Micronesia, the Gulf Coast of the United States and Mexico, the Nile Delta, the Gulf of Guinea, and the Bay of Bengal—specific vulnerable regions are identified in the FAR, SAR, RICC, and regional chapters of this report). Infrastructure hardening costs can be high if a decision were made to protect everything: The costs of protecting port facilities and coastal structures, raising wharves and quays, and reconstructing water gates and pumping stations for a 1-m sea-level rise in 39 prefectures in Japan has been estimated at 22 trillion Japanese yen (US$194 billion), or about 7% of annual GDP (Mimura and Harasawa, 2000). In cases in which neither retreat nor defense is feasible, flooding can be accommodated through infrastructure that is designed to reduce damage and evacuation planning to reduce loss of life. Bangladesh, for example, provides hardened storm shelters (Choudhury, 1998).
When extreme weather disasters happen in these regions as a result of tropical or extra-tropical cyclones, the total costs of damages become very large and, where insured, often cause serious problems for insurance carriers (see Chapter 8). The United States’ direct annual insured and uninsured costs for tropical cyclones (hurricanes), adjusting for inflation, averaged $1.6 billion (1995 US$) from 1950 to 1989 and $6.2 billion from 1989 to 1995 (Hebert et al., 1996). Estimates of worldwide annual direct costs have been placed at $10–15 billion annually (Pielke, 1997). Increased losses in the United States and elsewhere have occurred during a period in which the number and intensity of tropical cyclones actually was declining (Landsea et al., 1996; Pielke and Landsea, 1998). Thus, any future climate change-induced increase in tropical cyclone frequency or intensity remains a matter of great concern to insurers and coastal facilities planners. A single US$50 billion storm is not considered unlikely (Pielke and Landsea, 1998).
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