Diarrhoea remains a leading cause of mortality among children under five years of age, with over 99% of deaths occurring in low- and middle-income countries. Poor water quality, inadequate sanitation, poverty, undernutrition, and limited healthcare access contribute to this lingering problem, along with emerging environmental stressors driven by climate change. We analysed long-term spatial relationships between environmental, socioeconomic, and maternal/child factors using Demographic and Health Surveys and WorldClim data across eight South and Southeast Asian countries (n = 66,545 clusters; 3,143,811 child-level observations). We employed boosted regression trees to assess variable importance across five thematic phases: socio-economic, maternal, child, climate, and combined. We selected variables based on biological plausibility, collinearity checks, and completeness. We addressed uncertainty through multiple imputation and stochastic resampling, and we evaluated model performance using cross-validation. The main predictors of diarrhoea incidence included annual temperature variability, precipitation in the wettest month, maternal education, and household size. Higher annual temperature range (30-40 C) was associated with a ~ 39% increase in diarrhoea probability, while lower precipitation in the wettest month (< 600 mm) increased risk by ~ 29%, highlighting the role of drier conditions. We found that maternal education < 8 years increased diarrhoea probability by ~ 18%, and household sizes exceeding six members increased it by ~ 9%. Our findings emphasise the need for climate-resilient public-health policies that integrate social and environmental determinants of diarrhoea. Targeted interventions including improved maternal education, water and sanitation infrastructure, and resource management in densely populated households are necessary to mitigate diarrhoea risk in vulnerable regions under changing climate conditions.

The authors have declared no competing interest.

Funded jointly by The Kids Research Institute Australia.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

We obtained ethics approval from the Flinders University Human Research Ethics Committee (HEG8026-2).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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All relevant R code and data for the analyses and results available at doi:10.5281/zenodo.13864715. The Demographic Health Survey (DHS) data used in this study is available upon request from the DHS Program, subject to approval by the data custodians. Detailed information on how to request access can be found on their official website: https://dhsprogram.com/data/. The environmental data utilized in the analysis is freely accessible from WorldClim, a global climate database. It can be downloaded directly from their website: https://www.worldclim.org/data/index.html#google_vignette.

https://dhsprogram.com/data/

https://www.worldclim.org/data/index.html#google_vignette