The United Nations University (UNU) tool for flood hazard, exposure and vulnerability mapping using SAR remote sensing and open access socio-economic data.

Flood risk mapping is instrumental for flood mitigation, effective risk communication, economic impact assessment, and identifying the justice implications of floods. Lack of risk data often makes is difficult to develop risk maps for many parts of the world, especially in the Global South. The United Nations University Institute for Water, Environment and Health (UNU-INWEH) is developing a flood risk and vulnerability mapping tool for data-scare regions that leverage the recently available open access socio-economic data on population, GDP, relative wealth, and land use together with Sentinel-1 SAR satellite imagery. This tool applies an automatic flood mapping algorithm on the Google Earth Engine to generate flood hazard maps from inundation data time series. The hazard maps are overlaid with spatially represented socio-economic data to develop exposure and vulnerability maps. To showcase the applicability of the developed tool, we produced flood risk maps for the Ganges Brahmaputra and Meghna Basin, one of the world's most flooded, densely populated, and poor regions. Our alarming results reveal that 64% of the basin's population (582 million people) live in areas with medium-very high flood risk with half of them exposed to a high/very high risk of flooding. This has major justice and health implications that threaten a population group that are more vulnerable to the effects of natural disasters given their limited capacity to mitigate and adapt. This case study shows how the developed UNU tool holds promise as a decision support system for delineating flood risk zones in global river basins especially in the data sparse regions by providing a data driven approach to promote equitable flood risk management