River Flood Impact Forecasting to Support Humanitarian Anticipatory Action

Millions of people worldwide are affected by river floods each year. To facilitate early action, humanitarian organisations have adopted anticipatory action frameworks that link pre-agreed activities and their funding with forecasted peak river flow thresholds. However, the scale of humanitarian needs is primarily determined by flood impacts rather than hazard magnitude alone, limiting the effectiveness of streamflow-based triggers.

In the Humanitarian Action Challenges project we work closely with our humanitarian partners, UN OCHA and the Netherlands Red Cross, to engage with national Red Cross societies and key stakeholders in Ethiopia, Nigeria, and Uganda. The goal of the project is to move beyond streamflow thresholds alone to additionally provide impact forecasts, such as estimates of affected populations, in order to improve anticipatory action of humanitarian organisations. 

As a first step, and to assess the feasibility of this approach, we analyse past river flood events in Ethiopia, Nigeria, and Uganda. We combine flood extents derived from Global Flood Awareness System (GloFAS) discharge forecasts and JRC hazard maps with geospatial data on population exposure and vulnerability using the open-source risk assessment platform CLIMADA. Modelled affected populations are compared with reported impacts using an event severity ranking. No systematic bias is observed, with both over- and underestimation across events. Rankings are highly sensitive to the inclusion of flood protection standards from the FLOPROS dataset. Comparisons with remotely sensed flood extents and analyses of model drivers highlight key limitations and sources of uncertainty for trigger calibration. These preliminary insights support the development of impact forecasts and the design of impact-based triggers for anticipatory action by humanitarian partners.