Natural Disasters
The number and cost of natural
disasters—worldwide and in
North America—have increased
Throughout a long and continuous cycle of response and
recovery, mitigation and preparedness, North Americans
have tried to reduce their risk of and consequences from
disasters. Recent experience, however, suggests that disasters are becoming more frequent and expensive in spite of
advanced technology.
enormously….The cost is rising
not only because of the increased
frequency and severity of natural
disasters, but also because of the
growing tendency of people to
live in high-risk areas.
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The number and cost of natural disasters—worldwide and
in North America—have increased enormously (Changnon
et al. 1997). The list of events is long: the Mississippi flood
of 1993 (Box 9), the Mexico City earthquake of 1985, the
ice storm in eastern Canada and the northeastern United
States in 1998, and such costly and sometimes lethal hurricanes as Camille (1969), Gilbert (1988), Hugo (1989),
Andrew (1992), Pauline (1997), and Floyd (1999). And the
cost is mounting. The single most costly disaster insurance
year on the record was 1998. The cost is rising not only
because of the increased frequency and severity of natural
disasters, but also because of the growing tendency of
people to live in high-risk areas (Changnon et al. 1997).
Government post-disaster aid and property insurance that
covers extreme weather probably contribute to this tendency.
damage, injury, and death from hurricanes, tornadoes, and
particularly from the storm surges they generate can occur
in heavily populated regions. Hurricanes and tornadoes
occur most frequently in the central United States and
Florida (Parfit 1998) (map 15).
Our current understanding of disasters reflects to a much
greater degree the importance of the human pressures that
lead to unsafe conditions. Natural events are the triggers
that create disasters, but the occurrence of disasters is just
as much a function of society as it is of nature (Abley 1998).
Canada, Mexico, and the United States have all suffered
from short-term environmental thinking, which permitted activities that exacerbated the effects of some types of
natural disasters. Widespread deforestation, for example,
removes a watershed’s ability to soak up rainfall, thus causing floods far downstream during heavy rains. Engineering
waterways to make them more navigable creates deeper and
straighter channels, which often allow flash floods to move
faster and in greater volumes, with disastrous effects.
Certainly the El Niño episodes of the last two decades have
been the strongest of the past 120 years. And, as the
Americas are greatly affected by El Niño cycles, it is perhaps reasonable to expect that the storms it influences might
be similarly extreme (D’Agnese 2000). A number of scientists now think that recent climatic changes have already
increased the frequency and severity of some types of natural disasters, such as hurricanes, tornadoes, droughts and
floods, but the extent of this link is not yet known (Etkin
et al. 1998).
Building in riverine floodplains and along hurricane-prone
coasts virtually guarantees extensive property damage in
times of disaster. Nonetheless, if insurance coverage and
comprehensive disaster relief are available, such practices
will continue. Subsidized agriculture, flood insurance, and
the promise of governmental disaster relief have long
encouraged people to settle in the Mississippi floodplain
(Searchinger and Tripp 1993; Rasmussen 1994). In addition to causing human suffering, extreme events can wreak
havoc on ecosystems, triggering a domino effect of further
environmental damage. Droughts, for example, can lead to
dust storms, soil erosion, and forest fires.
Migration is a significant factor associated with disastrous
events. Since hurricane-prone coastal areas increasingly
attract new and expanded settlements, people may live in
high-risk areas because they do not know or care about
the risk of infrequent catastrophic events, because they do
not fully understand the risks, or because poverty or other
societal factors limit their choices. In the United States,
North American governments are beginning to step up programs to better inform the public of natural hazard risks
and to reduce the risk of loss of life, injuries, economic
costs, and destruction of natural and cultural resources.
Land-use planning that designates low-risk uses for areas
that are most vulnerable to natural hazards is an effective
method for mitigating impacts, but the practice is far from
Map 15
Hurricanes and Tornadoes in North America, 1970–96: Frequency and Resultant Loss of Life
Box 9
Connections: The Mississippi Flood
To minimize recurrent flooding and encourage settlement,
a series of levees and dikes were built along the Mississippi
River over many decades. The purpose of the structures
was to confine the river to a more stable channel. Though
seemingly successful during most years, the system has
proved inadequate and even harmful during exceptional
floods. In 1993, for example, property damage and erosion
were more severe than they would have been without the
controls (Searchinger and Tripp 1993).
Number of reported deaths
from hurricanes and tornadoes
1970–96
1–10
11–100
>100
Hawaii
Annual hurricane
landfall probability
less than 5%
5–9.9%
10–15%
Average annual number of
reported tornadoes 1970–96
By cutting the river off from the floodplain, the levees prevented water from spilling over into bordering wetlands.
These wetlands and temporary lakes that formerly acted
as storage areas for excess water were now inaccessible to
the main channel of the river. Flooding tributaries had
nowhere to go but the river proper. In many places, the levees have also destroyed wetlands and their rich web of life.
Among the major policy questions raised by the 1993 disaster was how the United States could shift to more
appropriate uses of flood-prone lands (Changnon 1996;
Bhowmik and Demissie 1996; Rasmussen 1994; Philippi
1996). An interagency review committee set up to address
the long-term future of the Mississippi basin recognized
the need for a more sustainable approach to development
and considered a variety of nonstructural alternatives,
including resettlement projects and wetland restoration
(Rasmussen 1994).
0–9
10–25
26–50
51–100
>100
Source: NG Maps 1998.
Note: No tornado data available for Mexico.
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routine. At a time of growing populations and deregulation, it is harder to stop development in areas that are only
occasionally flood-prone.
Since the frequency and ferocity of natural disasters is likely
to be altered in unclear but significant ways as a result of
future climate change, societies striving for sustainability
must learn to become more flexible. Past experience is one
useful guide that often tends to be overlooked. And precautionary approaches may be able to dramatically mitigate
the severity of future effects. Land use planning that encourages disaster-resistant buildings and transportation
networks in less vulnerable locations is one promising
strategy. Upholding national commitments to reduce greenhouse gas emissions is another. Clear contingency plans,
outlining what to do and how or whether to rebuild after
disaster strikes, are also important. Becoming a more
resilient, nimble, and sustainable region will likely require
unprecedented levels of cooperation among diverse
disciplines and multiple levels of government.
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