Excess risk in infant mortality among populations living in flood prone areas in Bangladesh: A cluster-matched cohort study over three decades, 1988-2017

The Ganges-Brahmaputra-Meghna river basin, running through Tibet, Nepal, Bhutan, Bangladesh and northern India, is home to more than 618 million people. Annual monsoons bring extensive flooding to the basin, with floods predicted to be more frequent and extreme due to climate change. Yet, evidence regarding the long-term impacts of floods on children’s health is lacking. In this analysis, we used high-resolution maps of recent large floods in Bangladesh to identify flood prone areas over the country. We then used propensity score techniques to identify, among 58,945 mothers interviewed in six DHS population-based surveys throughout Bangladesh, matched cohorts of exposed and unexposed mothers and leverage data on 150,081 births to estimate that living in flood prone areas was associated with an excess risk in infant mortality of 5.9 [2.8;8.9] additional deaths per 1000 births compared to living in non-flood prone areas over the 30-year period between 1988 and 2017. Finally, drawing on national-scale, high-resolution estimates of flood risk and population distribution, we estimated an excess of 170,136 [80,742;256,645] infant deaths over the past 30 years were attributable to living in flood-prone areas in Bangladesh, with marked heterogeneity in attributable burden by subdistrict and heterogeneity in excess risk over time, with a risk difference of 9.2 [2.9;15.5], 1.5 [-2.6;5.7] and 8.9 [3.7;14.2] per 1000 births for the 1988–1997; 1998–2007 and 2008–2017 decades respectively. Our approach demonstrates the importance of measuring longer-term health impacts from floods and provides a generalizable example for how to study climate-related exposures and long-term health effects.