A national scale assessment of direct and indirect flood impacts and social flood risk in India

Traditional approaches to impact assessment for weather-related hazards focus upon the direct impacts from those hazards, such as those due to physical contact with floodwaters. Examples include loss of life or injury due to drowning or accidents during flooding, or damage to buildings and infrastructure. Indirect impacts from flooding occur outside the inundated area, often as a result of disruption caused by direct impacts. Examples of indirect impacts include economic losses from business interruptions, reduced productivity, and repair costs, health impacts such as outbreaks of waterborne diseases or mental health issues, supply chain disruptions, affecting food, fuel, and essential goods. 

Impact-based forecasting and warning systems typically only assess direct impacts, however extreme weather events can affect far more people and assets than those directly exposed to the hazard.  

Building on a traditional assessment of direct impacts of the flood hazard, an assessment for India of the indirect impacts was carried out following a method developed for Denmark, by Prall et al. (2024). Hazard data was collected from the Copernicus fluvial flood maps. Exposure was calculated using WorldPop population datasets. Vulnerability was determined using the Indian 2011 census. Indirect impacts were calculated using data on critical infrastructure and applying an estimate of the impacted population. Assessments assume that impacts to critical infrastructure are weighted evenly, although the method allows for specific weightings to be applied.

Using 2011 census data, we determined social flood risk, where this reflects the potential adverse impact of flooding on people and communities, based on the interaction between flood hazard and social vulnerability. Social flood risk includes indicators that increase resilience (e.g. literacy, neighbourhood social capital) and those indicators that decrease resilience (e.g. age, wealth, disability, language). Social flood risk was then applied at the resolution of the Copernicus flood map grid cells (100 metres) and then aggregated to a district level.

The assessment of direct and indirect risks, together with the social flood risk, allows disaster risk reduction experts and practitioners to better understand more fully the populations and assets exposed to extreme weather events as well providing valuable insights into population resilience.

Our research has shown how a national scale assessment of direct and indirect impacts can be developed for India. Ultimately, such methods could be used as part of operational impact-based forecasting and warning systems, to more accurately predict the wider impacts, and thus improve preparedness and response to weather-related hazards.

This work builds on international collaboration through the Weather and Climate Science for Service Partnership (WCSSP) India programme, a UK–India programme advancing impact-based forecasting for high-impact weather in multi-risk and cascading hazard contexts.