Water Policy Brief, Issue 40, June 2018 - Dams and malaria in Africa: Time for action
Malaria transmission – associated with morbidity, mortality and constraining economic development – has been reduced by more than 40% in Africa in the twenty-first century. Large dams, essential to achieving Africa’s development goals, have nonetheless created a set of local conditions that have defied the broader twenty-first century progress. Dams typically increase the presence of small pools of water in which mosquitoes breed, resulting in proliferation of adult Anopheles mosquitoes; the vectors of malaria transmission. Overall, the annual impact of large dams on malaria in Africa is conservatively estimated at more than 1.1 million cases. In the absence of other changes, this cumulative impact is projected to exceed 2 million cases by the 2050s as a result of climate change and population growth. While there is a clear need to better mitigate these infrastructure-driven malaria cases, several tools and approaches for combatting the disease in the vicinity of reservoirs are currently not widely utilized. Predicting the malaria-enhancing effect of alternative dam options – now possible – can enable selection of disease-conscious development paths. Targeted manipulation of reservoir water levels at critical times holds potential to reduce malaria transmission. Ultimately, a range of options for reducing the adverse impacts of water resources development remain to be put into practice in Africa – resulting in avoidable disease burden.
Contribution of large dams to the malaria burden in Africa. More than 1.1 million malaria cases each year can be attributed to the presence of large dams in Africa. By the 2050s, this could exceed 2 million cases.
Impacts of dams on malaria are variable. Certain dams significantly increase malaria transmission, while other dams may produce minimal impact on transmission. Local conditions such as climate and topography at a dam site influence the degree to which a dam intensifies malaria.
Diversity of dams’ impacts presents opportunities. Expanded understanding of factors that affect the severity of a dam’s malariaenhancing effect can be used to consider impacts at alternative future sites. The slope of a reservoir’s seasonally-submerged area, for example, and climate at a reservoir site each influence the degree of malaria increase that a dam will produce. Consideration of differential impacts at different potential dam sites can enable selection of development options with fewer disease externalities.
Alternative dam operating regimes hold potential to contribute to reduced disease burden. Investigations into possible dam operation designed to disrupt Anopheles mosquito development around the Koka Reservoir, Ethiopia, suggest there is potential for malaria reduction with minimal disruption to conventional operating objectives (hydropower, irrigation). Around the Kariba Reservoir, shared between Zimbabwe and Zambia, understanding of malaria impacts of water levels may enable consideration of more circumspect management approaches.
Failure to pursue implementation of potential malaria control measures contributes to unnecessary disease burden. Valuable, impactful measures for controlling malaria are currently not being implemented. Given recent progress toward malaria control in Africa, dams increasingly reflect nodes of enhanced transmission