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Global Assessment Report on Disaster Risk Reduction 2011
Revealing Risk, Redefining Development
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1.3 Reducing disaster risk


The main opportunities for reducing risk lie in reducing vulnerability. This means addressing the underlying risk drivers by strengthening risk governance capacities. Extensive risks are largely shaped by these drivers. In contrast, intensive risks are more heavily determined by the location, severity and frequency of the associated hazard, meaning that there are limits to vulnerability reduction.

Governments cannot influence the severity of droughts, earthquakes, tsunamis and tropical cyclones, except in the case of weather-related hazards through international action to mitigate climate change. Similarly, the exposure of people and assets is largely fixed by the location of historical investments in infrastructure, urban and economic development, as well as by social and cultural attachment to places, or by geographical constraints such as on small islands. If hazard severity and exposure cannot be reduced, the main opportunities for reducing risk lie in reducing vulnerability.

Extensive risks are largely shaped by underlying risk drivers and can thus be more easily reduced by a strengthening of risk governance capacities. In contrast, intensive risks are more heavily determined by the location, severity and frequency of the associated hazard, meaning that there are limits to vulnerability reduction.

In the case of tropical cyclones, for example, the variation in mortality appears to be affected by a combination of three factors: the severity of the cyclone, the number of people exposed and GDP per capita, the latter being a reasonable proxy indicator of a country’s vulnerability. As Table 1.1 shows, GDP per capita explains 91 percent of the variance in mortality risk with Category 1 cyclones, but only 37.1 percent with powerful Category 4 cyclones. In contrast, the numbers of people exposed explains only 9 percent of the risk variance with Category 1 cyclones, but 62.9 percent with Category 4 cyclones. The implication is that if a country reduces its vulnerability, it can significantly reduce the mortality risk associated with Category 1 cyclones. Reducing the risk associated with Category 4 cyclones, however, particularly when accompanied by storm surges in low-lying coastal areas, is far more challenging.

Table 1.1 Contribution of cyclone severity, exposure and vulnerability parameters to tropical cyclone risk

Risk factors Correlation Category 1 Category 2 Category 3 Category 4
Population exposure to tropical cyclones Positive 9.0% 46.4% 45.1% 62.9%
GDP per capita Negative 91.0% 53.6% 46.3% 37.1%
Distance to city Positive Not significant Not significant 8.6% Not significant
  Total 100% 100% 100% 100%

Tropical cyclone severity is measured on the Saffir-Simpson scale in five Categories. Category 5 cyclones occur very infrequently but are the most destructive, while Category 1 cyclones are more frequent but less severe.
(Source: UNEP/GRID-Europe, 2010)

This does not imply that intensive risk cannot be reduced. All intensive risk is underpinned by vulnerability to some degree. As highlighted by the impact of Category 5 cyclone Yasi in Australia in February 2011, sound disaster management can go a long way to minimize mortality, even in the case of very severe cyclones. However, reducing vulnerability to very severe hazards may have unacceptably high costs and trade-offs. In the Cayman Islands, for example, building regulations specify resistance to a Category 3 cyclone. Increasing standards to withstand Category 4 or 5 cyclones would lead to an exponential increase in the cost of building, making the country less attractive for investment.

In practice, these trade-offs are often already reflected in codes and regulations. Many building codes specify protection against earthquakes that occur once every 475 years but not those which occur less frequently, and national insurance regulators may limit catastrophe insurance to risks with a return period of less than 1,500 years. Different countries value the trade-offs in different ways, however. The Netherlands, for example, has constructed its dykes to resist a 10,000-year storm surge (ECA, 2009

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ECA (Economics of Climate Adaptation). 2009. Shaping climate adaptation: A framework for decision-making. New York, USA: McKinsey & Company.
Available at http://www.mckinsey.com/App_Media/Images/Page_Images/Offices/SocialSector/PDF/ECA_Shaping_Climate%20Resilent_Development.pdf.
), but in most low- and middle-income countries, such investments are not affordable even if they were technically feasible and politically important.

In the case of destructive tsunamis as the examples of Lisbon and Callao illustrated, vulnerability may be almost binary: meaning that all people exposed to the hazard are vulnerable, irrespective of income and capacities. In the case of large cities exposed to tsunamis that may reach the shoreline in a matter of minutes,3  the effectiveness of early warning is relative. Even if civil engineering works that could protect a city against tsunamis were technically possible, it is doubtful whether the costs of their construction and maintenance would make economic sense given long return periods (World Bank, 2010a

x

World Bank. 2010a. Africa development indicators. Washington DC, USA: The World Bank.
.
).

It is not only the severity of hazards such as these that makes intensive risks more difficult to reduce. It is also the unexpectedness of events for which there may be no historical precedent, at least in living memory, and for which societies are thus not prepared. All other factors being equal, earthquake mortality for example, is lower in countries that experience more earthquakes, and is higher where earthquakes occur only infrequently (Keefer et al., 2010

x

Keefer, P., Neumayer, E. and Plumper, T. 2010. Earthquake propensity and the politics of mortality prevention. Policy Research Working Paper 4952. Washington DC, USA: The World Bank.
.
). In the absence of frequent major earthquakes, governments are less likely to find political incentives to invest in disaster risk management. If a major earthquake does occur, the absence of such investment leads to higher actual mortality.



3 Notwithstanding this affirmation, in tsunami-exposed Pagang, Indonesia, building artificial hills has been proposed, called Tsunami Evacuation Raised Earth Parks (TEREPs), that would allow the vertical evacuation of people in the case of a tsunami warning (GeoHazards International, 2010

x

GeoHazards International. 2010. Tsunami preparedness: Feasibility study of vertical evacuation structures in Sumatra. Online database. Palo Alto, USA: GeoHazards International.
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). However, the effectiveness of this approach has yet to be proved in practice.

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