Major impacts of climate change on human health are likely to occur via changes in the magnitude and frequency of extreme events (see Table 3-10), which trigger a natural disaster or emergency. In developed countries, emergency preparedness has decreased the total number of tropical cyclone-related deaths (see Section 7.2.2). However, in developed countries, studies indicate an increasing trend in the number and impacts (deaths, injuries, economic losses) of all types of natural disasters (IFRC, 1998; Munich Re, 1999). Some of the interannual variability in rates of persons affected by disasters may be associated with El Niño (Bouma et al., 1997a). The average annual number of people killed by natural disasters between 1972 and 1996 was about 123,000. By far the largest number of people affected (i.e., in need of shelter or medical care) are in Asia, and one study reveals that Africa suffers 60% of all disaster-related deaths (Loretti and Tegegn, 1996).

Populations in developing countries are much more affected by extreme events. Relative to low socioeconomic conditions, the impact of weather-related disasters in poor countries may be 20-30 times larger than in industrialized countries. For example, floods and drought associated with the El Niño event of 1982-1983 led to losses of about 10% in gross national product (GNP) in countries such as Bolivia, Chile, Ecuador, and Peru (50% of their annual public revenue) (Jovel, 1989).

Disasters occur when climate hazards and population vulnerability converge. Factors that affect vulnerability to disasters are shown in Figure 9-1. The increase in population vulnerability to extreme weather is primarily caused by the combination of population growth, poverty, and environmental degradation (Alexander, 1993). Concentration of people and property in high-risk areas (e.g., floodplains and coastal zones) also has increased. Degradation of the local environment also may contribute to vulnerability (see Chapter 7).

The health impacts of natural disasters include (Noji, 1997):

• Physical injury.
• Decreases in nutritional status, especially in children.
• Increases in respiratory and diarrheal diseases resulting from crowding of survivors, often with limited shelter and access to potable water
• Impacts on mental health, which in some cases may be long-lasting
• Increased risk of water-related diseases as a result of disruption of water supply or sewage systems
• Release and dissemination of dangerous chemicals from storage sites and waste disposal sites into floodwaters.

Extreme weather events cause death and injury directly. However, substantial indirect health impacts also occur because of damage to the local infrastructure and population displacement (see also Section 9.10). Following disasters, fatalities and injuries can occur as residents return to clean up damage and debris (Philen et al., 1992). Bereavement, property loss, and social disruption may increase the risk of depression and mental health problems (WHO, 1992). For example, cases of post-traumatic stress disorder were reported in the United States up to 2 years after Hurricane Andrew (Norris et al., 1999).

Floods are associated with particular dangers to human populations (Menne et al., 1999). Climate change may increase the risk of river and coastal flooding (see Chapters 4 and 6). The health impacts of floods may be divided into the immediate, medium, and long terms. Immediate effects are largely death and injuries caused by drowning and being swept against hard objects. Medium-term effects include increases in communicable diseases such as those caused by ingestion of contaminated water (e.g., cholera, hepatitis A), contact with contaminated water (e.g., leptospirosis—see Section 9.7.9.1), or respiratory diseases resulting from overcrowding in shelters. A study in populations displaced by catastrophic floods in Bangladesh in 1988 found that diarrhea was the most common illness, followed by respiratory infection. Watery diarrhea was the most common cause of death for all age groups under 45 (Siddique et al., 1991). In rural Bangladesh and Khartoum, Sudan, the proportion of severely malnourished children increased after flooding (Woodruff et al., 1990; Choudhury and Bhuiya, 1993). Also, in the aftermath of flooding, molds and fungi may grow on interior surfaces, providing a potent stimulus to allergic persons (American Academy of Pediatrics, 1998).

In China, floods experienced over the past few years have been particularly severe. In 1996, official national statistics showed 200 million people affected by flooding: There were more than 3,000 deaths, and 363,800 people were injured; 3.7 million houses were destroyed, and 18 million houses were damaged. Direct economic loses exceeded US$12 billion (IFRC 1997). In 1998, official national statistics showed 200 million people affected by flooding, more than 3,000 deaths, and 4 million houses damaged; direct economic losses exceeded US$20 billion (National Climate Centre of China, 1998). Nevertheless, the vulnerability of the Chinese population has been reduced by a combination of better preparedness, including sophisticated warning systems, and relief efforts. In the longer term, reforestation may reduce the risk of flooding in these regions.

In developed countries, physical and disease risks from flooding are greatly reduced by a well-maintained flood control and sanitation infrastructure and public health measures, such as monitoring and surveillance activities to detect and control outbreaks of infectious disease. However, the experience of the central European floods of 1997, when more than 100 people died, showed that even in industrialized countries floods can have a major impact on health and welfare. In Poland, 6,000 km2 were flooded, and 160,000 people were evacuated from their homes. The cost of the damage was estimated at US$3 billion [2.7% of 1996 gross domestic product (GDP)]. In the Czech Republic, 50,000 people were evacuated and damage was estimated at US$1.8 billion (3.7% of GDP) (IFRC, 1998). There was an increase in cases of leptospirosis in the Czech Republic (Kriz et al., 1998). Floods also have an important impact on mental health in the affected community (WHO, 1992; Menne et al., 1999). Increases in suicide, alcoholism, and psychological and behavioral disorders, particularly among children, were reported following floods in Poland in 1997 (IFRC 1998).

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