Worldwide, about 800 million people lack access to an improved water source. In its most basic form, an improved water supply is a well or protected spring that protects water from outside contamination. Lack of access to clean water helps explain why15% of all deaths of children under 5 worldwide are caused by diarrheal diseases. While many factors are involved, water quality and quantity can both be impacted by weather, and thus climate change is likely to adversely affect this disease burden. This is because residents of developing countries lack the adaptive capacity to cope with seasonal precipitation and temperature variations which will likely increase in much of the world as a result of climate change. Increased rainfall can flush pathogens into unprotected water supplies while decreased rainfall can make water less accessible although such effects vary in magnitude and even direction between climates.
To test this hypothesis, Alexander et al (2013), investigated the effect of weather on diarrheal disease rates in Botswana. Researchers correlated 30 years of monthly diarrheal disease reports from Botswanan health facilities with a number of climate variables including rainfall, temperature and vapor pressure. They found a distinct bimodal cyclical pattern to diarrheal disease rates with peaks during the wet and dry seasons. Of the two peaks, the highest diarrheal disease rates occurred in the dry season and were 20% higher than the yearly mean. The authors speculate that the dry season peak could be due to a number of factors including changes in water quality or quantity, poor sanitation, increased water intake (and hence increased pathogen intake), the sharing of water transfer devices, food spoilage or increases in fly activity. They also found that rainfall, minimum temperature and vapor pressure were able to explain up to 58% of diarrhea case variability highlighting the importance of those variables. The authors theorize that vapor pressure might influence the survival of diarrheal pathogens although the mechanisms are unclear given that the relationship is species specific and can be either negative or positive.
These results contradict previous studies that found diarrheal diseases to be the highest during the wet season. The authors hypothesize this could be due to the arid nature of Botswana’s climate and the increase of fly activity during the dry hot season. Also in contrast to some previous studies, they found that minimum temperatures were the only temperature parameter to be positively associated with diarrheal disease rates. This could be due to the minimum temperature’s significant seasonal variation in this region although the researchers were unclear about the mechanisms. Overall, the authors suggest that the climate drivers of diarrheal disease are spatially focused and that high-resolution studies are the best way to elucidate climate-diarrhea relationships.
Although the study did not explicitly predict diarrhea rates under future climate scenarios, the regional climate is expected to get 2.5-3% hotter and 5-15% drier in the coming decades. Given that the authors found diarrhea rates to be highest during the dry season, it is likely that diarrhea rates will increase significantly in Botswana in the coming decades.
Alexander, K. A., Carzolio, M., Goodin, D., & Vance, E. (2013). Climate change is likely to worsen the public health threat of diarrheal disease in Botswana. International journal of environmental research and public health,10(4), 1202-1230.