Box 83 Drought in the Amazon

In the dry season of 2005, an intense drought affected the western and central part of the Amazon region, especially Bolivia, Peru and Brazil. In Brazil alone, 280,000 to 300,000 people were affected (see, e.g., Folha, 2006; Socioambiental, 2006). The drought was unusual because it was not caused by an El Niño event, but was linked to a circulation pattern powered by warm seas in the Atlantic - the same phenomenon responsible for the intense Atlantic hurricane season (CPTEC, 2005). There were increased risks to health due to water scarcity, food shortages and smoke from forest fires. Most affected were rural dwellers and riverine traditional subsistence farmers with limited spare resources to mobilise in an emergency. The local and national governments in Brazil provided financial assistance for the provision of safe drinking water, food supplies, medicines and transportation to thousands of people isolated in their communities due to rivers drying up (World Bank, 2005).

also affected. The spatial distribution, intensity and seasonality of meningococcal (epidemic) meningitis appear to be strongly linked to climatic and environmental factors, particularly drought, although the causal mechanism is not clearly understood (Molesworth et al., 2001,2002a, b, 2003). Climate plays an important part in the interannual variability in transmission, including the timing of the seasonal onset of the disease (Molesworth et al., 2001; Sultan et al., 2005). The geographical distribution of meningitis has expanded in West Africa in recent years, which may be attributable to environmental change driven by both changes in land use and regional climate change (Molesworth et al., 2003).

The transmission of some mosquito-borne diseases is affected by drought events. During droughts, mosquito activity is reduced and, as a consequence, the population of nonimmune persons increases. When the drought breaks, there is a much larger proportion of susceptible hosts to become infected, thus potentially increasing transmission (Bouma and Dye, 1997; Woodruff et al., 2002). In other areas, droughts may favour increases in mosquito populations due to reductions in mosquito predators (Chase and Knight, 2003). Other drought-related factors that may result in a short-term increase in the risk for infectious disease outbreaks include stagnation and contamination of drainage canals and small rivers. In the long term, the incidence of mosquito-borne diseases such as malaria decreases because the mosquito vector lacks the necessary humidity and water for breeding. The northern limit of Plasmodium falciparum malaria in Africa is the Sahel, where rainfall is an important limiting factor in disease transmission (Ndiaye et al., 2001). Malaria has decreased in association with long-term decreases in annual rainfall in Senegal and Niger (Mouchet et al., 1996; Julvez et al., 1997). Drought events are also associated with dust storms and respiratory health effects (see Section 8.2.6). Droughts are also associated with water scarcity; the risks of water-washed diseases are addressed in Section 8.2.5.

8.2.4 Food safety

Several studies have confirmed and quantified the effects of high temperatures on common forms of food poisoning, such as salmonellosis (D'Souza et al., 2004; Kovats et al., 2004; Fleury et al., 2006). These studies found an approximately linear increase in reported cases with each degree increase in weekly or monthly temperature. Temperature is much less important for the transmission of Campylobacter (Kovats et al., 2005; Louis et al., 2005; Tam et al., 2006).

Contact between food and pest species, especially flies, rodents and cockroaches, is also temperature-sensitive. Fly activity is largely driven by temperature rather than by biotic factors (Goulson et al., 2005). In temperate countries, warmer weather and milder winters are likely to increase the abundance of flies and other pest species during the summer months, with the pests appearing earlier in spring.

Harmful algal blooms (HABs) (see Chapter 1, Section 1.3.4.2) produce toxins that can cause human diseases, mainly via consumption of contaminated shellfish. Warmer seas may thus contribute to increased cases of human shellfish and reef-fish poisoning (ciguatera) and poleward expansions of these disease distributions (Kohler and Kohler, 1992; Lehane and Lewis, 2000; Hall et al., 2002; Hunter, 2003; Korenberg, 2004). For example, sea-surface temperatures influence the growth of Gambierdiscus spp., which is associated with reports of ciguatera in French Polynesia (Chateau-Degat et al., 2005). No further assessments of the impact of climate change on shellfish poisoning have been carried out since the TAR.

Vibrio parahaemolyticus and Vibrio vulnificus are responsible for non-viral infections related to shellfish consumption in the USA, Japan and South-East Asia (Wittmann and Flick, 1995; Tuyet et al., 2002). Abundance is dependent on the salinity and temperature of the coastal water. A large outbreak in 2004 due to the consumption of contaminated oysters (V. parahaemolyticus) was linked to atypically high temperatures in Alaskan coastal waters (McLaughlin et al.,

Another example of the implications that climate change can have for food safety is the methylation of mercury and its subsequent uptake by fish and human beings, as observed in the Faroe Islands (Booth and Zeller, 2005; McMichael et al.,

8.2.5 Water and disease

Climate-change-related alterations in rainfall, surface water availability and water quality could affect the burden of water-related diseases (see Chapter 3). Water-related diseases can be classified by route of transmission, thus distinguishing between water-borne (ingested) and water-washed diseases (caused by lack of hygiene). There are four main considerations to take into account when evaluating the relationship between health outcomes and exposure to changes in rainfall, water availability and quality:

• linkages between water availability, household access to improved water, and the health burden due to diarrhoeal diseases;

• the role of extreme rainfall (intense rainfall or drought) in facilitating water-borne outbreaks of diseases through piped water supplies or surface water;

• effects of temperature and runoff on microbiological and chemical contamination of coastal, recreational and surface waters;

• direct effects of temperature on the incidence of diarrhoeal disease.

Access to safe water remains an extremely important global health issue. More than 2 billion people live in the dry regions of the world and suffer disproportionately from malnutrition, infant mortality and diseases related to contaminated or insufficient water (WHO, 2005). A small and unquantified proportion of this burden can be attributed to climate variability or climate extremes. The effect of water scarcity on food availability and malnutrition is discussed in Section 8.2.3, and the effect of rainfall on outbreaks of mosquito-borne and rodentborne disease is discussed in Section 8.2.8.

Childhood mortality due to diarrhoea in low-income countries, especially in sub-Saharan Africa, remains high despite improvements in care and the use of oral rehydration therapy (Kosek et al., 2003). Children may survive the acute illness but may later die due to persistent diarrhoea or malnutrition. Children in poor rural and urban slum areas are at high risk of diarrhoeal disease mortality and morbidity. Several studies have shown that transmission of enteric pathogens is higher during the rainy season (Nchito et al., 1998; Kang et al., 2001). Drainage and storm water management is important in low-income urban communities, as blocked drains are one of the causes of increased disease transmission (Parkinson and Butler, 2005).

Climate extremes cause both physical and managerial stresses on water supply systems (see Chapters 3 and 7), although well-managed public water supply systems should be able to cope with climate extremes (Nicholls, 2003; Wilby et al., 2005). Reductions in rainfall lead to low river flows, reducing effluent dilution and leading to increased pathogen loading. This could represent an increased challenge to water-treatment plants. During the dry summer of 2003, low flows of rivers in the Netherlands resulted in apparent changes in water quality (Senhorst and Zwolsman, 2005).

Extreme rainfall and runoff events may increase the total microbial load in watercourses and drinking-water reservoirs (Kistemann et al., 2002), although the linkage to cases of human disease is less certain (Schwartz and Levin, 1999; Aramini et al., 2000; Schwartz et al., 2000; Lim et al., 2002). A study in the USA found an association between extreme rainfall events and monthly reports of outbreaks of water-borne disease (Curriero et al., 2001). The seasonal contamination of surface water in early spring in North America and Europe may explain some of the seasonality in sporadic cases of water-borne diseases such as cryptosporidiosis and campylobacteriosis (Clark et al., 2003; Lake et al., 2005). The marked seasonality of cholera outbreaks in the Amazon is associated with low river flow in the dry season (Gerolomo and Penna, 1999), probably due to pathogen concentrations in pools.

Higher temperature was found to be strongly associated with increased episodes of diarrhoeal disease in adults and children in Peru (Checkley et al., 2000; Speelmon et al., 2000; Checkley et al., 2004; Lama et al., 2004). Associations between monthly temperature and diarrhoeal episodes have also been reported in the Pacific islands, Australia and Israel (Singh et al., 2001; McMichael et al., 2003b; Vasilev, 2003).

Although there is evidence that the bimodal seasonal pattern of cholera in Bangladesh is correlated with sea-surface temperatures in the Bay of Bengal and with seasonal plankton abundance (a possible environmental reservoir of the cholera pathogen, Vibrio cholerae) (Colwell, 1996; Bouma and Pascual, 2001), winter peaks in disease further inland are not associated with sea-surface temperatures (Bouma and Pascual, 2001). In many countries cholera transmission is primarily associated with poor sanitation. The effect of sea-surface temperatures in cholera transmission has been most studied in the Bay of Bengal (Pascual et al., 2000; Lipp et al., 2002; Rodo et al., 2002; Koelle et al., 2005). In sub-Saharan Africa, cholera outbreaks are often associated with flood events and faecal contamination of the water supplies.

8.2.6 Air quality and disease

Weather at all time scales determines the development, transport, dispersion and deposition of air pollutants, with the passage of fronts, cyclonic and anticyclonic systems and their associated air masses being of particular importance. Airpollution episodes are often associated with stationary or slowly migrating anticyclonic or high pressure systems, which reduce pollution dispersion and diffusion (Schichtel and Husar, 2001; Rao et al., 2003). Airflow along the flanks of anticyclonic systems can transport ozone precursors, creating the conditions for an ozone event (Lennartson and Schwartz, 1999; Scott and Diab, 2000; Yarnal et al., 2001; Tanner and Law, 2002). Certain weather patterns enhance the development of the urban heat island, the intensity of which may be important for secondary chemical reactions within the urban atmosphere, leading to elevated levels of some pollutants (Morris and Simmonds, 2000; Junk et al., 2003; Jonsson et al.,

82.6.1 Ground-level ozone

Ground-level ozone is both naturally occurring and, as the primary constituent of urban smog, is also a secondary pollutant formed through photochemical reactions involving nitrogen oxides and volatile organic compounds in the presence of bright sunshine with high temperatures. In urban areas, transport vehicles are the key sources of nitrogen oxides and volatile organic compounds. Temperature, wind, solar radiation, atmospheric moisture, venting and mixing affect both the emissions of ozone precursors and the production of ozone (Nilsson et al., 2001a, b; Mott et al., 2005). Because ozone formation depends on sunlight, concentrations are typically highest during the summer months, although not all cities have shown seasonality in ozone concentrations (Bates,

2005). Concentrations of ground-level ozone are increasing in most regions (Wu and Chan, 2001; Chen et al., 2004).

Exposure to elevated concentrations of ozone is associated with increased hospital admissions for pneumonia, chronic obstructive pulmonary disease, asthma, allergic rhinitis and other respiratory diseases, and with premature mortality (e.g., Mudway and Kelly, 2000; Gryparis et al., 2004; Bell et al., 2005, 2006; Ito et al., 2005; Levy et al., 2005). Outdoor ozone concentrations, activity patterns and housing characteristics, such as the extent of insulation, are the primary determinants of ozone exposure (Suh et al., 2000; Levy et al., 2005). Although a considerable amount is known about the health effects of ozone in Europe and North America, few studies have been conducted in other regions.

8.2.6.2 Effects of weather on concentrations of other air pollutants

Concentrations of air pollutants in general, and fine particulate matter (PM) in particular, may change in response to climate change because their formation depends, in part, on temperature and humidity. Air-pollution concentrations are the result of interactions between variations in the physical and dynamic properties of the atmosphere on time-scales from hours to days, atmospheric circulation features, wind, topography and energy use (McGregor, 1999; Hartley and Robinson, 2000; Pal Arya, 2000). Some air pollutants demonstrate weather-related seasonal cycles (Alvarez et al., 2000; Kassomenos et al., 2001; Hazenkamp-von Arx et al., 2003; Nagendra and Khare, 2003; Eiguren-Fernandez et al., 2004). Some locations, such as Mexico City and Los Angeles, are predisposed to poor air quality because local weather patterns are conducive to chemical reactions leading to the transformation of emissions, and because the topography restricts the dispersion of pollutants (Rappengluck et al., 2000; Kossmann and Sturman, 2004).

Evidence for the health impacts of PM is stronger than that for ozone. PM is known to affect morbidity and mortality (e.g., Ibald-Mulli et al., 2002; Pope et al., 2002; Kappos et al., 2004; Dominici et al., 2006), so increasing concentrations would have significant negative health impacts.

8.2.63 Air pollutants from forest fires

In some regions, changes in temperature and precipitation are projected to increase the frequency and severity of fire events (see Chapter 5). Forest and bush fires cause burns, damage from smoke inhalation and other injuries. Large fires are also accompanied by an increased number of patients seeking emergency services (Hoyt and Gerhart, 2004). Toxic gaseous and particulate air pollutants are released into the atmosphere, which can significantly contribute to acute and chronic illnesses of the respiratory system, particularly in children, including pneumonia, upper respiratory diseases, asthma and chronic obstructive pulmonary diseases (WHO, 2002a; Bowman and Johnston, 2005; Moore et al., 2006). For example, the 1997 Indonesia fires increased hospital admissions and mortality from cardiovascular and respiratory diseases, and negatively affected activities of daily living in South-East Asia (Sastry, 2002; Frankenberg et al., 2005; Mott et al., 2005). Pollutants from forest fires can affect air quality for thousands of kilometres (Sapkota et al., 2005).

8.2.6.4 Long-range transport of air pollutants

Changes in wind patterns and increased desertification may increase the long-range transport of air pollutants. Under certain atmospheric circulation conditions, the transport of pollutants, including aerosols, carbon monoxide, ozone, desert dust, mould spores and pesticides, may occur over large distances and over time-scales typically of 4-6 days, which can lead to adverse health impacts (Gangoiti et al., 2001; Stohl et al., 2001; Buchanan et al., 2002; Chan et al., 2002; Martin et al., 2002; Ryall et al., 2002; Ansmann et al., 2003; He et al., 2003; Helmis et al., 2003; Moore et al., 2003; Shinn et al., 2003; Unsworth et al., 2003; Kato et al., 2004; Liang et al., 2004; Tu et al., 2004). Sources of such pollutants include biomass burning, as well as industrial and mobile sources (Murano et al., 2000; Koe et al., 2001; Jaffe et al., 2003, 2004; Moore et al., 2003).

Windblown dust originating in desert regions of Africa, Mongolia, Central Asia and China can affect air quality and population health in remote areas. When compared with nondust weather conditions, dust can carry large concentrations of respirable particles, trace elements that can affect human health, fungal spores and bacteria (Claiborn et al., 2000; Fan et al., 2002; Shinn et al., 2003; Cook et al., 2005; Prospero et al., 2005; Xie et al., 2005; Kellogg and Griffin, 2006). However, recent studies have not found statistically significant associations between Asian dust storms and hospital admissions in Canada and Taiwan (Chen and Tang, 2005; Yang et al., 2005a; Bennett et al., 2006). Evidence suggests that local mortality, particularly from cardiovascular and respiratory diseases, is increased in the days following a dust storm (Kwon et al., 2002; Chen et al.,

8.2.7 Aeroallergens and disease

Climate change has caused an earlier onset of the spring pollen season in the Northern Hemisphere (see Chapter 1, Section 1.3.7.4; D'Amato et al., 2002; Weber, 2002; Beggs, 2004). It is reasonable to conclude that allergenic diseases caused by pollen, such as allergic rhinitis, have experienced some concomitant change in seasonality (Emberlin et al., 2002; Burr et al., 2003). There is limited evidence that the length of the pollen season has also increased for some species. Although there are suggestions that the abundance of a few species of air-borne pollens has increased due to climate change, it is unclear whether the allergenic content of these pollen types has changed (pollen content remaining the same or increasing would imply increased exposure) (Huynen and Menne, 2003; Beggs and Bambrick,

2005). Few studies show patterns of increasing exposure for allergenic mould spores or bacteria (Corden et al., 2003; Harrison et al., 2005). Changes in the spatial distribution of natural vegetation, such as the introduction of new aeroallergens into an area, increases sensitisation (Voltolini et al., 2000; Asero, 2002). The introduction of new invasive plant species with highly allergenic pollen, in particular ragweed (Ambrosia artemisiifolia), presents important health risks; ragweed is spreading in several parts of the world (Rybnicek and Jaeger, 2001; Huynen and Menne, 2003; Taramarcaz et al., 2005; Cecchi et al., 2006). Several laboratory studies show that increasing CO2 concentrations and temperatures increase ragweed pollen production and prolong the ragweed pollen season (Wan et al., 2002; Wayne et al., 2002; Singer et al., 2005; Ziska et al., 2005; Rogers et al., 2006a) and increase some plant metabolites that can affect human health (Ziska et al., 2005; Mohan et al., 2006).

8.2.8 Vector-borne, rodent-borne and other infectious diseases

Vector-borne diseases (VBD) are infections transmitted by the bite of infected arthropod species, such as mosquitoes, ticks, triatomine bugs, sandflies and blackflies. VBDs are among the most well-studied of the diseases associated with climate change, due to their widespread occurrence and sensitivity to climatic factors. There is some evidence of climate-change-related shifts in the distribution of tick vectors of disease, of some (non-malarial) mosquito vectors in Europe and North America, and in the phenology of bird reservoirs of pathogens (see Chapter 1 and Box 8.4).

Northern or altitudinal shifts in tick distribution have been observed in Sweden (Lindgren and Talleklint, 2000; Lindgren and Gustafson, 2001) and Canada (Barker and Lindsay, 2000), and altitudinal shifts have been observed in the Czech Republic (Daniel et al., 2004). Geographical changes in tick-borne infections have been observed in Denmark (Skarphedinsson et al., 2005). Climate change alone is unlikely to explain recent increases in the incidence of tick-borne diseases in Europe or North America. There is considerable spatial heterogeneity in the degree of increase of tick-borne encephalitis, for example, within regions of Europe likely to have experienced similar levels of climate change (Patz, 2002; Randolph, 2004; Sumilo et al., 2006). Other explanations cannot be ruled out, e.g., human impacts on the landscape, increasing both the habitat and wildlife hosts of ticks, and changes in human behaviour that may increase human contact with infected ticks (Randolph, 2001).

In north-eastern North America, there is evidence of recent micro-evolutionary (genetic) responses of the mosquito species Wyeomyia smithii to increased average land surface temperatures and earlier arrival of spring in the past two decades (Bradshaw and Holzapfel, 2001). Although not a vector of human disease, this species is closely related to important arbovirus vector species that may be undergoing similar evolutionary changes.

Cutaneous leishmaniasis has been reported in dogs (reservoir hosts) further north in Europe, although the possibility of previous under-reporting cannot be excluded (Lindgren and Naucke, 2006). Changes in the geographical distribution of the sandfly vector have been reported in southern Europe (Aransay et al., 2004; Afonso et al., 2005). However, no study has investigated the causes of these changes. The re-emergence of kala-azar (visceral leishmaniasis) in cities of the semi-arid Brazilian north-eastern region in the early 1980s and 1990s was caused by rural-urban migration of subsistence farmers who had lost their crops due to prolonged droughts (Franke et al., 2002; Confalonieri, 2003).

8.2.8.1 Dengue

Dengue is the world's most important vector-borne viral disease. Several studies have reported associations between

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