There are multiple pressures on human settlements that interact with climate
change. The discussion in this chapter shows that these other effects are more
important in the short run; climate is a potential player in the long run. For
example, urban population in the least-developed countries currently is growing
at about 5% yr-1, compared with 0.3% yr-1 in highly industrialized
Providing for this rapidly urbanizing population will be much higher on most
countries’ agendas than longer term issues with climate change.
Other environmental problems will tend to interact with climate change, adversely
affecting human settlements. For example, 25–90% of domestic energy supply in
the developing world is met by biomass resources, especially in small urban
centers (Barnes et al., 1998). In some countries, 11–20% of all deforestation
may be attributable to charcoal production (Ribot, 1993), much of it to meet
urban needs. If biomass growth is slowed via climate change effects, the impacts
on biomass may be compounded.
Deforestation and cultivation of marginal lands can compound the effects of
extreme events. For example, floods resulting from Hurricane Mitch, though not
caused by climate change, illustrate the fact that poor watershed management
can contribute to flooding and landslides—which, in turn, causes loss of life
and destroys infrastructure and the means of livelihood. Mitch cost Honduras
80% and Nicaragua 49% of one year’s GDP (FAO, 1999). Poor watershed management
and technical failures has contributed to loss of life in landslides in Sri
Lanka, Peru, Brazil, several European countries, and the United States (Katupotha,
Urban water resources already are in extremely short supply in 19 Middle Eastern
and African countries (IPCC, 1998) and in cities in many parts of the world,
where as many as 60% of poorer residents may not have access to reliable water
supplies (Foronda, 1998). Poor urban water management may be responsible for
losses through leakage of 20–50% in cities in the developing world and even
in some cities in the industrialized world (WRI, 1996). If climate change makes
water more scarce—by increasing demand (even in regions that currently are not
particularly short of water, such as Great Britain—see Arnell, 1998) or by reducing
supply (reduced surface runoff, exacerbation of water quality problems as a
result of warmer temperatures and reduced flows, or salinization of coastal
aquifers resulting from sea-level rise)—water supply problems would be exacerbated.
Liquid waste disposal is a significant problem in urban areas as diverse as
Chimbote, Peru (Foronda, 1998); Buenos Aires, Argentina (Pirez, 1998); Cotonou,
Benin (Dedehouanou, 1998); and Chicago, USA (Changnon and Glantz, 1996). There
are two ways in which climate could interact with this problem: reductions in
supplies of water with which wastes are diluted and the impact of more severe
flooding episodes that overtop sewer systems and treatment plants (Walsh and
Pittock, 1998). Where most inhabitants rely on pit latrines and wells, flooding
spreads excreta from pit latrines everywhere and contaminates wells (Boko, 1991,
1993, 1994). Land-use changes associated with urbanization also have reduced
the absorptive capacity of many river basins, increasing the ratio of runoff
to precipitation and making flooding more likely (Changnon and Demissie, 1996).
Large urban areas, especially in the developed world, depend on extended “linkage
systems” for their viability (Timmerman and White, 1997; Rosenzweig and Solecki,
2000). They depend on imports from the local area, region, nation, and even
the world for everything from raw material and food, to product and waste exports
and communications. These linkage systems often are vulnerable to severe storms,
floods, and other severe weather events. Management, redundancy, and robustness
of these interlocking systems is a top priority for developed world settlements
especially, but increasingly so for the developing world (Timmerman and White,
7.6.1. Key Vulnerabilities
Key climate-related sensitivities in urban areas of the world include water
supply and the effects of extreme events (primarily flooding) on infrastructure
in river floodplains and coastal zones. These areas should be considered sensitive
to climate change. To the extent that sensitive settlements coincide with conditions
of poverty and lack of technical infrastructure, these settlements also will
be particularly vulnerable to climate change.
7.6.2. Potential for Nonlinear Interactions and Synergistic
Because of their role as centers for administration and commerce, urban areas
integrate all of the environmental effects that visit a society and to some
extent buffer their human occupants from natural environmental fluctuations.
However, these urban areas still may be affected by several stresses that interact
with each other in a nonlinear fashion (Rosenzweig and Solecki, 2000; Wilbanks
and Wilkinson, 2001). Whatever cash economy there is in a country tends to reside
in its biggest cities, and trade routes also focus on these areas. These are
two very important coping mechanisms. Thus, for example, climate-related food
shortages are more likely to be experienced in urban areas as an increase in
migrants from the countryside or loss of business in agriculture-related business
rather than as famine per se.
Once populations are housed in urban settlements, there are other potential
interactions among climate effects that lead to nonlinear impacts on them. Flooding
events that are beyond the designed capacity of settlement infrastructure are
a case in point, especially in cases in which systems already may be degraded.
Urban flooding can overwhelm sewage treatment systems, thereby increasing the
risk of disease at the same time that water treatment systems are compromised,
health services are disrupted, disease vector species are driven into close
contact with people, and people are exposed to the elements because of lost
housing. Outbreaks of epidemics are always a risk under such circumstances,
whereas the breakdown of any single one of the affected systems might be merely
inconvenient. Although all of these effects and mechanisms are well understood,
however, it is not possible to predict impacts quantitatively at this time.
Table 7-3 shows the primary synergistic effects
between climate-related factors that may affect human settlements and the primary
types of settlements or industries affected. Each cell identifies a synergistic
effect between the climate impact featured in the row and another effect shown
in the column. For example, climate-related impacts of flooding, landslides,
and fire are compounded when they occur in settlements that also might be crowded
by migration. Likewise, flooding in particular exacerbates water pollution and
human health impacts and probably would compound problems in obtaining drinking
water and transportation. In addition, the agricultural base and energy supplies
could be affected in regions that already are water-deficient.
Air and water pollution effects of climate change would be worse if the health
of human populations already is compromised (e.g., asthma attacks may be more
severe or prolonged in a weakened population). Charlot-Valdieu et al. (1999)
argue for reducing some stresses in a multiple-stress context to handle other
stresses in a more sustainable manner.
Access to energy, clean water, sanitation, and selected other resources is
essential to maintain human settlements and the health of the populations within.
Flooding, landslides, or fire resulting from extreme weather could compound
the shortage of resources by destroying critical infrastructure (floods in Honduras
in 1998 and Mozambique in 2000 are examples of the phenomenon under current
climate) and, in the case of water, polluting the sources. Similarly, water
pollution reduces the effective water supply by making some sources unusable.