Flash floods are among the world’s deadliest natural hazards. They cause more than 5 000 deaths annually and have severe social, economic and environmental impacts. Flash floods account for approximately 85% of all floods and have the highest mortality rate among all categories of flooding. Flash floods are sudden and short, with a time frame of less than six hours between the observable causative event and the flood itself, which tends to have a high peak discharge. Flash floods have enough power to change the course of rivers, bury houses in mud, and sweep away or destroy whatever stands in their path. They are complex hydrometeorological events that are hard to predict. Therefore, preparing for them requires expertise in hydrology and meteorology combined with knowledge of local conditions.
Flash Flood Guidance System with Global Coverage
When Hurricane Mitch struck Central America in 1998, it caused more than 11 000 casualties and destroyed hundreds of thousands of homes. Flash floods, floods, landslides and mudslides brought on by heavy rainfall destroyed entire villages, and the majority of the countries’ crops and infrastructure were destroyed. Total damages amounted to more than US$ 5 billion.
In the wake of these catastrophic events, the U.S. Agency for International Development’s (USAID) Office of Foreign Disaster Assistance (OFDA) initiated a project to coordinate the development of an early warning system for flash floods in the region. In 2001, the Hydrologic Research Center, in collaboration with U.S. National Oceanic and Atmospheric Administration (NOAA), began the development of the regional Flash Flood Guidance System (FFGS) to generate flash flood warnings. Then in 2007 World Meteorological Congress approved the implementation of FFGS worldwide through projects developed jointly by the WMO in collaboration with NOAA, the Hydrologic Research Center, and USAID/OFDA.
Today, FFGS is providing early warnings in over 60 countries to some three billion people – 40% of the world’s population – as a result of 13 regional and 2 national FFGS projects. And more projects are under development worldwide. Environment and Climate Change Canada is funding the implementation of FFGS as part of the ongoing Building Resilience to High-Impact Hydrometeorological Events through Strengthening Multi-Hazard Early Warning Systems in Small Island Developing States and Southeast Asia project. The CREWS Initiative’s Seamless Operational Forecast Systems and Technical Assistance for Capacity Building in West Africa project, launched in 2019, is developing FFGS in three countries in that region.
Objectives of the System
FFGS was developed to improve the capacity of National Meteorological and Hydrological Services (NMHSs) to issue flash flood warnings and alerts in order to mitigate the adverse impacts of hydrometeorological hazards. The FFGS enhances collaboration between national meteorological and hydrological services, disaster management agencies and other stakeholders and implements state-of-the-art hydrometeorological forecasting models and technology. It provides extensive training to the hydrologists, meteorologists and disaster managers. Since flash floods often cross-national boundaries, regional FFGS projects and cooperation are essential: thus FFGS fosters national, regional and global development and collaboration.
Flash Flood Guidance System’ Objectives
FFGS has been developed as a tool to provide meteorological and hydrological forecasters with both real-time information and diagnostic products to improve their capacity to produce and issue timely and accurate flash flood warnings. Since the implementation of FFGS, most of the countries using it have had access for the first time to products that enable them to issue flash flood warnings and provide response-agencies with the ability to mobilize rapidly.
FFGS products include:
- Quality-controlled precipitation estimates gathered from radar and satellites
- Rainfall measurements from rain-gauges
- Average soil-moisture and flash flood guidance
- Prognostic products such as quantitative precipitation forecasts from Numerical Weather Prediction models
- Snow products that provide data on snow coverage, snow melt and snow water equivalent;
- and risk- and threat-assessment products related to flash floods.
Special FFGS modules and components are available to assess landslide threats, flash flood events in urban areas and riverine routing. The world's urban population is expected to increase from 55% in 2018 (some 4.2 billion people) to 68% by 2050. With this significant rise in concentrated population centres, it is essential that cities around the world invest in reducing flash flood risks.
Landslide Threat Index showing the likelihood of landslide occurrence in Central America (left) and Flash Flood Guidance System Products (right).
Flash Flood Guidance SystemTechnical Components.
Training of hydrologists, meteorologists and disaster managers is an integral part of implementing FFGS and critical for establishing sustainable, local capabilities within the participating NMHSs. Since its implementation started a decade ago, more than 400 meteorological and hydrological forecasters have received extensive FFGS training. An international FFGS Global Workshop, hosted by the Turkish State Meteorological Organization in November 2019 in Antalya, Turkey, gathered 169 experts from 59 countries to share experiences, showcase accomplishments, determine challenges, identify service gaps and establish recommended practices. Their goal was to augment the sustainability of FFGS.
Participants recognized that the implementation of FFGS over the last decade had led to a significant reduction in the loss of life and property. They called upon national governments to recognize FFGS as an effective means of safeguarding their countries from flash floods – particularly as the global population increases, urban areas grow, and societies continue to encroach upon regions prone to flash floods. The need for flash flood early warning systems is paramount.
The Antalya Statement details the main findings of the workshop and outlines recommendations for implementing FFGS in the future. It highlights that further investments are needed in emerging science and technology in order to strengthen and sustain FFGS. Efforts also have to be directed towards: Improving governance; improving training and capabilities; increasing visibility of the role and benefits of FFGS; and mobilizing additional resources. To help ensure FFGS’ sustainability, participants recommended that technical issues be better addressed. Among their recommendations were calls to adopt a more formal, inclusive, research-to-operations process and to make it easier to access and distribute digital data from automated rain gauges to the Flash Flood Guidance System.
Integration into multi-hazard system
Fiji FFGS MapServer interface showing flash flood risk product including vulnerability of infrastructure.
FFGS has used data from WMO Severe Weather Forecasting Project as an input to create flash flood risk and threat products wherever geographically alignment made it possible. Work is already underway to improve FFGS’ predictive capabilities by providing more accurate forecasts with longer lead times – both are critical for disaster risk reduction.
Based on these positive results, the 2019 World Meteorological Congress decided to integrate three projects – FFGS, Severe Weather Forecasting Project, and Coastal Inundation Forecasting Initiative – into the larger Multi-Hazard Early Warning System. Thereby, it will create a system that integrates coastal flooding, flash flooding, and severe weather prediction capabilities. In accordance with that decision, the Hydrological Coordination Panel recommended the preparation of a strategic outline to ensure a smooth integration of the three projects and the support of sub-projects by relevant experts.
The FFGS MapServer interface already provides meteorological and hydrological forecasters with the ability to overlay FFGS products with Geographic Information System (GIS) data, including: Demographic data, vulnerability maps, evacuation facilities, infrastructure, and educational and health facilities. By providing hydrometeorological and disaster management agencies with information about the vulnerabilities of infrastructure, NMHSs could help minimize the adverse impacts of weather-related disasters and reduce fatalities, damage and loss.
Scientists expect the frequency and severity of flash floods to increase due primarily to climate change, population growth and land-use changes. Development and implementation of FFGS is, therefore, more crucial than ever to protect communities, safeguard economies and save countless lives. Together, FFGS partners, participating countries and regions will continue to mitigate the impacts of flash floods by enhancing early warning capabilities.
Milica Dordevic, WMO Secretariat
Petra Mutic, WMO Secretariat
Hwirin Kim, WMO Secretariat