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1. The Effects of ENSO on Human Well-Being
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1. The Effect of ENSO
on Human Well-Being
The ENSO phenomenon has some substantial effects on world climate; it is associated with risk changes of weather-related disasters such as hurricanes and tropical storms (typhoons), floods and droughts, forest and bush fires, as well as increasing the risk of certain vector-borne diseases such as malaria. Also, long-term climate change may affect the frequency and intensity of weather events associated with the El Niño phenomenon. As such, studies of ENSO can highlight signs of early disaster warning to improve disaster and disease outbreak preparedness in the future[i].
ENSO – which comprises of two parts: (1) changes in sea surface temperatures in the Pacific Ocean (El Niño) and (2) changes in atmospheric pressure across the Pacific basin (Southern Oscillation) – is associated with extreme weather events such as floods and drought in countries surrounding the Pacific and in other parts of the world through distant connections. Changes in precipitation, temperature and hurricane activity caused by the ENSO phenomenon all invariably impact the effect of El Niño on human health[ii].
Studies have shown a relationship between the El Niño cycle and changes in the risk of diseases transmitted by mosquitoes such as malaria and dengue, which are both sensitive to climate and weather variations.
The El Niño ‘disaster cycle’
Studies have identified associations between ENSO and drought-related disasters. For instance, the frequency of a drought-related disaster is twice as high in the year following an El Niño (year +1) compared with other years[iii]. Also, the ENSO cycle has a strong relationship with the annual rate of persons affected by natural disasters[iv].
Figure 2.1 shows the total number of persons affected by natural disasters and El Niño years; an increase in the number of persons affected is closely associated with El Niño years[v]. Figure 2.2 illustrates the El Niño cycle – disaster risk is usually low before an El Niño and high during or after the occurrence of an El Niño (years 0, +1)[vi]. Figure 2.3, based on USAID disaster data, illustrates which countries are more likely to suffer a drought-related disaster following the onset of El Niño (year +1)[vii].
The conclusion of these various findings is that El Niño, while not certainly responsible for any individual extreme event, increases the possibility of extreme climate events occurring. However, regional and local factors can either mitigate or amplify the influences of ENSO events as ENSO-related anomalies are more often than not localized.
ENSO – which comprises of two parts: (1) changes in sea surface temperatures in the Pacific Ocean (El Niño) and (2) changes in atmospheric pressure across the Pacific basin (Southern Oscillation) – is associated with extreme weather events such as floods and drought in countries surrounding the Pacific and in other parts of the world through distant connections. Changes in precipitation, temperature and hurricane activity caused by the ENSO phenomenon all invariably impact the effect of El Niño on human health[ii].
Studies have shown a relationship between the El Niño cycle and changes in the risk of diseases transmitted by mosquitoes such as malaria and dengue, which are both sensitive to climate and weather variations.
The El Niño ‘disaster cycle’
Studies have identified associations between ENSO and drought-related disasters. For instance, the frequency of a drought-related disaster is twice as high in the year following an El Niño (year +1) compared with other years[iii]. Also, the ENSO cycle has a strong relationship with the annual rate of persons affected by natural disasters[iv].
Figure 2.1 shows the total number of persons affected by natural disasters and El Niño years; an increase in the number of persons affected is closely associated with El Niño years[v]. Figure 2.2 illustrates the El Niño cycle – disaster risk is usually low before an El Niño and high during or after the occurrence of an El Niño (years 0, +1)[vi]. Figure 2.3, based on USAID disaster data, illustrates which countries are more likely to suffer a drought-related disaster following the onset of El Niño (year +1)[vii].
The conclusion of these various findings is that El Niño, while not certainly responsible for any individual extreme event, increases the possibility of extreme climate events occurring. However, regional and local factors can either mitigate or amplify the influences of ENSO events as ENSO-related anomalies are more often than not localized.
Drought and Famine
Rates of people affected by either drought or famine account for about half of all disaster victims worldwide[viii]. In arid regions where precipitation patterns are either highly seasonal or variable, food production is often susceptible to the ENSO cycle due to its association with drought in numerous vulnerable regions simultaneously. Although food shortages and famine are caused by complex social and environmental issues, climate variability is nevertheless still a significant factor.
Rates of people affected by either drought or famine account for about half of all disaster victims worldwide[viii]. In arid regions where precipitation patterns are either highly seasonal or variable, food production is often susceptible to the ENSO cycle due to its association with drought in numerous vulnerable regions simultaneously. Although food shortages and famine are caused by complex social and environmental issues, climate variability is nevertheless still a significant factor.
Hurricanes and Tropical Storms
Originating between 5°N and 20°S of the equator, tropical cyclones (also known as typhoons in the Pacific and hurricanes in the Caribbean) are severe tropical storms whose impacts are mostly due to flooding associated with the “storm surge” when the cyclone makes landfall[ix]. ENSO cycles affect tropical cyclones in the following ways:
Originating between 5°N and 20°S of the equator, tropical cyclones (also known as typhoons in the Pacific and hurricanes in the Caribbean) are severe tropical storms whose impacts are mostly due to flooding associated with the “storm surge” when the cyclone makes landfall[ix]. ENSO cycles affect tropical cyclones in the following ways:
During an El Niño (year +1)
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During a La Niña (year +1)
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Health Impacts of El Niño
Apart from extreme weather phenomena, non-catastrophic weather can also have significant impacts on human health. For instance, outbreaks of malaria are closely-linked to rainfall events and the subsequent abundance of mosquitoes. The seasonality of many diseases also highlights the relationships between weather, climate and disease which may be distributed or transmitted by cold-blooded insect vectors such as mosquitoes.
Disease carrying insect vectors which breed in water depend heavily on the availability of surface water; evidence has linked the abundance of mosquitoes to heavy rainfall events and the insects become responsible for the transmission of malaria and other viral diseases such as dengue and yellow fever.
Temperature fluctuations also impact the transmission of vector-borne diseases. Increases in temperature reduce both the intrinsic incubation period of the pathogen (e.g. malaria parasite, dengue fever virus) and the amount of need required for vectors to become infectious. Temperature increases also accelerate vector life cycles or allow vectors to spread to previously unreachable areas due to the cold temperatures before. Temperatures may also have an impact on human behaviour and movement with regards to disease exposure[x].
Apart from extreme weather phenomena, non-catastrophic weather can also have significant impacts on human health. For instance, outbreaks of malaria are closely-linked to rainfall events and the subsequent abundance of mosquitoes. The seasonality of many diseases also highlights the relationships between weather, climate and disease which may be distributed or transmitted by cold-blooded insect vectors such as mosquitoes.
Disease carrying insect vectors which breed in water depend heavily on the availability of surface water; evidence has linked the abundance of mosquitoes to heavy rainfall events and the insects become responsible for the transmission of malaria and other viral diseases such as dengue and yellow fever.
Temperature fluctuations also impact the transmission of vector-borne diseases. Increases in temperature reduce both the intrinsic incubation period of the pathogen (e.g. malaria parasite, dengue fever virus) and the amount of need required for vectors to become infectious. Temperature increases also accelerate vector life cycles or allow vectors to spread to previously unreachable areas due to the cold temperatures before. Temperatures may also have an impact on human behaviour and movement with regards to disease exposure[x].