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Alt nuachta3 Meitheamh 2019

Improving the global prediction of river flooding

JRC develops a new method to improve the early detection of floods up to 6 weeks ahead.

To improve and extend the forecasting skills in the Global Flood Awareness System (GloFAS), the new method develops flood thresholds which are range-dependent and thus adaptive to the weather forecasts.

The adaptive thresholds are able to compensate for forecast drifts, important for an earlier flood warning.

Through this research, a key step has been taken in the evolution of the GloFAS and similar systems which may lead to the extension from the current 30-day to a 6-week forecasting.


A 21-year weather forecast-consistent dataset has been used to derive thresholds with global coverage and a forecast range up to six weeks.

These have been compared with thresholds derived from ERA5, a state of the art atmospheric reanalysis used to run the baseline simulation for the years 1986-2017 and to give a best guess of the present hydrological states.

Number of weeks during which constant flood thresholds are consistent with those for streamflow forecasts in the coming 6 weeks.
Number of weeks during which constant flood thresholds are consistent with those for streamflow forecasts in the coming 6 weeks.
© EU 2019


The comparison provides evidence that the adaptive flood thresholds can differ significantly from the constant thresholds, currently in use.

This is caused by the differences in the statistics of extreme precipitation between the ERA5 meteorological reanalysis data and the weather forecasts, and which tend to increase with the forecast lead time.

Range-dependent flood thresholds in two river outlets
Range-dependent flood thresholds in two river outlets
© EU 2019


Evidence shows that the use of constant thresholds for 30-day flood forecasting, as currently used in GloFAS, is statistically correct only in 30% to 40% of the global river network.

However, the range-dependent thresholds of weekly duration improve the flood monitoring and early warning, particularly over longer forecasting horizons.

Global Flood Awareness System

The Global Flood Awareness System (GloFAS), jointly developed by the European Commission and the European Centre for Medium-Range Weather Forecasts (ECMWF), is a global hydrological forecast and monitoring system.
It couples state-of-the art weather forecasts with a hydrological model and provides downstream countries with information on upstream river conditions as well as continental and global overviews.

The system produces daily flood forecasts and monthly seasonal streamflow outlooks. It has been fully operational as a Copernicus Emergency Management Service since April 2018.

Towards operational use

Before the new method can be used in operations, it will first be tested and evaluated to assess the limits of its predictability and compare results with the current operational version of GloFAS.

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Range-dependent thresholds for global flood early warning


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3 Meitheamh 2019