Invited Perspective: Climate Changes the Effectiveness of Water, Sanitation, and Hygiene Interventions

There is growing evidence that climate change is reshaping the global distribution of infectious diseases, including diarrheal diseases,¹ a leading killer of young children.² Interventions are urgently needed that can reduce diarrheal diseases in a changing climate. However, changing climate conditions can also alter the effectiveness of key water, sanitation, and hygiene (WASH) interventions commonly used to prevent diarrheal diseases. For example, drought can reduce the availability of safe drinking water, heavy rainfall can flood latrines and mobilize pathogens, and extreme weather events can destroy water and sanitation infrastructure.^3–5 Climate change may also alter safe drinking water use and handwashing behaviors in low resource settings.^6,7

There remain large gaps in our understanding of how well current WASH interventions will prevent diarrheal diseases under future climate conditions. The science here is challenging—it involves interactions between multiple climate conditions that may affect the survival and spread of enteric pathogens, and an intervention (or set of interventions) designed to reduce exposure and, ultimately, disease outcomes. In many cases, risk varies over time, owing, in part, to variability in climate, adding further complexity and creating the potential for intervention impacts to vary temporally. Ideally, interventions can dampen risk generally and provide protection during windows of peak risk.

In a research article in this issue of Environmental Health Perspectives, Nguyen et al.⁸ reevaluated the impact of a randomized controlled trial of WASH interventions to reduce diarrheal illness in young children in Bangladesh,⁹ evaluating whether the effect of these interventions varied based on recent weather conditions. The authors made smart use of the fact that participants were asked to self-report diarrheal illness in children at different points in the year, pairing these outcomes with climate data. They found that WASH interventions were most effective during the rainy season, shortly after heavy rainfall, and when temperatures were high. Conversely, the effectiveness of the interventions were low, and possibly null, during cooler, drier periods.

This study provides direct evidence that the effectiveness of WASH in preventing diarrheal illness can vary with climate. WASH interventions provided maximum protection during periods of highest risk. In control households, diarrhea prevalence was highest during hot, wet periods; in intervention households, diarrhea prevalence did not increase with rainfall, and the relationship between diarrhea prevalence and temperature was dampened. It remains to be seen how these findings generalize to other contexts. The prevalence of diarrhea in the study population (5.7% prevalence in controls) was markedly lower than in a parallel study in Kenya (27.1% prevalence in controls).¹⁰ In regions with higher burden of diarrheal diseases or a different mix of pathogens, the ways in which climate alters the effectiveness of similar WASH interventions may differ.

Research is needed to clarify which interventions will reduce the risk of diarrheal diseases under different climate scenarios and contexts. This requires at least two complementary pursuits. First, we need to identify the climate conditions that govern windows of peak enteric infection risk. This is a multidimensional problem, given that an array of climate conditions can influence the incidence of diarrheal diseases, from short-term weather to interannual climate phenomena.^4,11 In addition, we now recognize that combinations of climate conditions can influence the spread of enteric pathogens. For example, rainfall following dry periods can deliver a pulse of pathogens to surface water, leading to increased incidence of diarrheal diseases.¹² Analytical approaches that evaluate the contributions of multiple climate conditions and interactions between these conditions to diarrheal diseases are needed.

Second, we need to evaluate the extent to which the effectiveness of WASH interventions varies in relation to climate conditions. Nguyen et al. provide a template for such research.⁸ Their work bears replicating in different regions where the level of exposure to enteric pathogens, pathogen composition, and climate conditions may differ, as well as across different WASH interventions. The growing availability of publicly available in situ and modeled climate data products at fine spatial resolution opens the possibility of such research. Rigorous studies will consider an array of both climate conditions and WASH interventions while accounting for multiple hypothesis testing.

Similarly, it is critical to consider climate variability when evaluating the effectiveness of WASH interventions. Studies of the impact of WASH on diarrheal outcomes risk spurious conclusions if they ignore climate. Those that do consider climate have the added benefit of deepening our mechanistic understanding of the role of climate on diarrheal disease dynamics and WASH effectiveness.

Global climate change is altering local climate, from extended drought to wetter conditions to heighted risks of extreme weather, creating opportunities for increased spread of enteric pathogens. Ideally, we will confront these changes with a set of interventions that are robust to climate change and can provide protection during high-risk time windows. Doing so will require an evidence base that can define how and when the effects of these interventions change in response to climate.

Refers to https://doi.org/10.1289/EHP13807

Conclusions and opinions are those of the individual authors and do not necessarily reflect the policies or views of EHP Publishing or the National Institute of Environmental Health Sciences.