8.2.2 Wind, storms and floods

Floods are low-probability, high-impact events that can overwhelm physical infrastructure, human resilience and social organisation. Floods are the most frequent natural weather disaster (EM-DAT, 2006). Floods result from the interaction of rainfall, surface runoff, evaporation, wind, sea level and local topography. In inland areas, flood regimes vary substantially depending on catchment size, topography and climate. Water management practices, urbanisation, intensified land use and forestry can substantially alter the risks of floods (EEA, 2005). Windstorms are often associated with floods.

Major storm and flood disasters have occurred in the last two decades. In 2003, 130 million people were affected by floods in China (EM-DAT, 2006). In 1999, 30,000 died from storms followed by floods and landslides in Venezuela. In 2000/2001, 1,813 died in floods in Mozambique (IFRC, 2002; Guha-Sapir et al., 2004). Improved structural and non-structural measures, particularly improved warnings, have decreased mortality from floods and storm surges in the last 30 years (EEA, 2005); however, the impact of weather disasters in terms of social and health effects is still considerable and is unequally distributed (see Box 8.2). Flood health impacts range from deaths, injuries, infectious diseases and toxic contamination, to mental health problems (Greenough et al., 2001; Ahern et al., 2005).

In terms of deaths and populations affected, floods and tropical cyclones have the greatest impact in South Asia and Latin America (Guha-Sapir et al., 2004; Schultz et al., 2005). Deaths recorded in disaster databases are from drowning and severe injuries. Deaths from unsafe or unhealthy conditions following the extreme event are also a health consequence, but such information is rarely included in disaster statistics (Combs et al., 1998; Jonkman and Kelman, 2005). Drowning by storm surge is the major killer in coastal storms where there are large numbers of deaths. An assessment of surges in the past 100 years found that major events were confined to a limited number of regions, with many events occurring in the Bay of Bengal, particularly Bangladesh (Nicholls, 2003).

Populations with poor sanitation infrastructure and high burdens of infectious disease often experience increased rates of diarrhoeal diseases after flood events. Increases in cholera (Sur et al., 2000; Gabastou et al., 2002), cryptosporidiosis (Katsumata et al., 1998) and typhoid fever (Vollaard et al., 2004) have been reported in low- and middle-income countries. Flood-related increases in diarrhoeal disease have also been reported in India (Mondal et al., 2001), Brazil (Heller et al., 2003) and Bangladesh (Kunii et al., 2002; Schwartz et al., 2006). The floods in Mozambique in 2001 were estimated to have caused over 8,000 additional cases and 447 deaths from diarrhoeal disease in the following months (Cairncross and Alvarinho, 2006).

The risk of infectious disease following flooding in high-income countries is generally low, although increases in respiratory and diarrhoeal diseases have been reported after floods (Miettinen et al., 2001; Reacher et al., 2004; Wade et al., 2004). An important exception was the impact of Hurricanes Katrina and Rita in the USA in 2005, where contamination of water supplies with faecal bacteria led to many cases of diarrhoeal illness and some deaths (CDC, 2005; Manuel, 2006).

Flooding may lead to contamination of waters with dangerous chemicals, heavy metals or other hazardous substances, from storage or from chemicals already in the environment (e.g., pesticides). Chemical contamination following Hurricane Katrina in the USA included oil spills from refineries and storage tanks, pesticides, metals and hazardous waste (Manuel, 2006). Concentrations of most contaminants were within acceptable short-term levels, except for lead and volatile organic compounds (VOCs) in some areas (Pardue et al., 2005). There are also health risks associated with long-term contamination of soil and sediment (Manuel, 2006); however, there is little published evidence demonstrating a causal effect of chemical contamination on the pattern of morbidity and mortality following flooding events (Euripidou and Murray, 2004; Ahern et al., 2005). Increases in population density and accelerating industrial development in areas subject to natural disasters increase the probability of future disasters and the potential for mass human exposure to hazardous materials released during disasters (Young et al., 2004).

There is increasing evidence of the importance of mental disorders as an impact of disasters (Mollica et al., 2004; Ahern et al., 2005). Prolonged impairment resulting from common mental disorders (anxiety and depression) may be considerable. Studies in both low- and high-income countries indicate that the mental-health aspect of flood-related impacts has been insufficiently investigated (Ko et al., 1999; Ohl and Tapsell, 2000; Bokszczanin, 2002; Tapsell et al., 2002; Assan-arigkornchai et al., 2004; Norris et al., 2004; North et al., 2004; Ahern et al., 2005; Kohn et al., 2005; Maltais et al., 2005). A systematic review of post-traumatic stress disorder in high-income countries found a small but significant effect following disasters (Galea et al., 2005). There is also evidence of medium- to long-term impacts on behavioural disorders in young children (Durkin et al., 1993; Becht et al., 1998; Bokszczanin, 2000, 2002).

Vulnerability to weather disasters depends on the attributes of the person at risk (including where they live, age, income, education and disability) and on broader social and environmental factors (level of disaster preparedness, health sector responses and environmental degradation) (Blaikie et al., 1994; Menne, 2000; Olmos, 2001; Adger et al., 2005; Few and Matthies, 2006). Poorer communities, particularly slum dwellers, are more likely to live in flood-prone areas. In the USA, lower-income groups were most affected by Hurricane Katrina, and low-income schools had twice the risk of being flooded compared with the reference group (Guidry and Margolis, 2005).

High-density populations in low-lying coastal regions experience a high health burden from weather disasters, such as settlements along the North Sea coast in north-west Europe, the Seychelles, parts of Micronesia, the Gulf Coast of the USA and Mexico, the Nile Delta, the Gulf of Guinea, and the Bay of Bengal (see Chapter 6). Environmentally degraded areas are particularly vulnerable to tropical cyclones and coastal flooding under current climate conditions.