Impact-based flood early warning in Lao PDR and Cambodia

Floods are among the most destructive natural hazards globally, with Southeast Asia being particularly vulnerable due to socioeconomic and geographical factors. Climate change exacerbates this vulnerability, increasing the frequency and intensity of flooding events and heightening the risks to millions of people and critical infrastructures. To address these challenges, disaster risk management is transitioning from traditional hazard-based to impact-based forecasting (IBF), which focuses on predicting the consequences of flood events. IBF emphasizes actionable insights, such as the number of people affected or disruptions to essential services, enabling more targeted early actions and decision-making.

This work shows the development and implementation of an operational impact-based flood forecasting and early warning system for five pilot river basins in Cambodia and Lao People's Democratic Republic (PDR). The system integrates the use of the Continuum distributed hydrological model (see Alfieri et al., 2024) calibrated with dedicated discharge measurements, 30 m resolution inundation maps generated for seven constant probabilities of occurrence with the REFLEX model (Arcorace et al., 2024), and a risk assessment model implemented for seven asset categories including direct economic damage on built-up, population affected, crop land affected, grazing land affected, roads affected, education facilities and health facilities affected. The system is updated twice daily with four different global and limited area numerical weather predictions (NWP), enabling forecasting of flood impacts up to five days ahead of their occurrence and thus assisting hydro-meteorological forecasters and disaster managers in their daily monitoring.

A key feature of this system is a co-production platform for generating standardized warning bulletins, allowing rapid dissemination of actionable information. This automation significantly reduces the time required for decision-making and prioritization during emergencies, enhancing disaster response capabilities. By aligning with international initiatives like the Sendai Framework and the Early Warnings for All, this system represents a critical advancement in flood risk management, promoting resilience and minimizing disaster impacts in Southeast Asia.