River Discharge

Risksvv0

Responsible:Niccolò Calandri

River Discharge

Overview

River discharge measures the volume of water (in m³/s) passing through a river cross-section per unit of time. It is one of the fundamental hydrological indicators for assessing water availability, flood risk, and river drought within and around a study area. This KPI presents the historical time series of river discharge based on data from the Open-Meteo Flood API, fed by the global hydrological model GloFAS (Global Flood Awareness System), developed by ECMWF and the European Commission.

River discharge is an ecologically important indicator: extreme variations (floods or prolonged low-flow periods) directly impact aquatic biodiversity, water quality, groundwater recharge, and the availability of riparian habitats. The historical trend enables identification of seasonal anomalies, extreme events, and structural changes in the hydrological regime linked to climate change.

Calculation Methodology

Data are sourced from the Open-Meteo Flood API (WRD_OPNMF_99), which delivers river discharge forecasts and historical time series with a spatial resolution of 5 km and temporal coverage from 1984 to the present. The underlying model is GloFAS-ERA5 for the historical period and GloFAS v4 for projections.

Calculation pipeline:

Georeferencing — identification of the nearest GloFAS pixel to the centroid of the study polygon (5 km resolution)
Time series extraction — retrieval of daily river discharge values (m³/s) for the full available period
Temporal aggregation — calculation of monthly and annual means for trend visualisation
Normalisation — values are presented both as absolute discharge (m³/s) and as anomaly relative to the reference climatology
Visualisation — the KPI generates a time-series chart; no quality level (A–E) is assigned, as this is a continuous monitoring indicator

Note: This is a visualisation/monitoring KPI: it is not associated with A–E quality ranges, but provides a historical discharge trend chart to support hydrological risk assessment.

Unit: cubic metres per second (m³/s)

Data Sources

Code	Name	Provider	Resolution	Availability
`WRD_OPNMF_99`	Open-Meteo Flood API	Open-Meteo / GloFAS / ECMWF	5 km	1984 — present

Chart Interpretation

The chart shows the historical river discharge trend over time. Key risk indicators are:

Condition	Discharge	Risk
Flood	Well above historical mean	Flood risk
Normal flow	Within 1 standard deviation of the mean	Ordinary conditions
Moderate low flow	50–80% of historical mean	Water stress
Severe low flow	< 50% of historical mean	River drought risk

Technical Notes

The 5 km resolution of the GloFAS model may not accurately represent small watercourses
The value refers to the nearest pixel to the polygon centroid; for large polygons, it may not correspond to the watercourse of interest
The historical series from 1984 enables multi-decadal trend analyses
Open-Meteo data are updated daily with a lag of approximately 5 days
River discharge data must be generated from the KPI itself

References

Alfieri, L., Lorini, V., Hirpa, F.A., Harrigan, S., Zsoter, E., Prudhomme, C., Salamon, P. (2020). "A global streamflow reanalysis for 1980–2018". Journal of Hydrology X, 6, 100049.
Copernicus Emergency Management Service (2024). "GloFAS — Global Flood Awareness System". ECMWF / European Commission. https://global.copernicus.eu/glofas
Open-Meteo (2024). "Flood API documentation". https://open-meteo.com/en/docs/flood-api

Data Sources & References

Sources

WRD_OPNMF_99

Methodology

Data from the Open-Meteo Flood API (WRD_OPNMF_99), 5 km resolution, 1984–present coverage. Hydrological model: GloFAS-ERA5 (historical) and GloFAS v4 (projections), developed by ECMWF and the European Commission. Process: (1) identification of the nearest GloFAS pixel to the polygon centroid; (2) extraction of the daily river discharge time series (m³/s); (3) monthly/annual aggregation; (4) anomaly calculation relative to the reference climatology. Visualisation KPI: no A–E quality levels.

River Discharge

Overview

Calculation Methodology

Calculation pipeline:

Georeferencing — identification of the nearest GloFAS pixel to the centroid of the study polygon (5 km resolution)

Time series extraction — retrieval of daily river discharge values (m³/s) for the full available period

Temporal aggregation — calculation of monthly and annual means for trend visualisation

Normalisation — values are presented both as absolute discharge (m³/s) and as anomaly relative to the reference climatology

Visualisation — the KPI generates a time-series chart; no quality level (A–E) is assigned, as this is a continuous monitoring indicator

Note: This is a visualisation/monitoring KPI: it is not associated with A–E quality ranges, but provides a historical discharge trend chart to support hydrological risk assessment.

Unit: cubic metres per second (m³/s)

Code

Name

Provider

Resolution

Availability

WRD_OPNMF_99

Open-Meteo Flood API

Open-Meteo / GloFAS / ECMWF

5 km

1984 — present

Condition

Discharge

Risk

Flood

Well above historical mean

Flood risk

Normal flow

Within 1 standard deviation of the mean

Ordinary conditions

Moderate low flow

50–80% of historical mean

Water stress

Severe low flow

< 50% of historical mean

River drought risk

Data Sources & References

Sources

WRD_OPNMF_99