The forecasts are produced by analysing the current status and trend of water levels and discharges in various stretches of water and on the basis of models in such a way that early warnings, particularly flood alerts, can be given to the authorities and the population.
1. The products of the hydrological forecasts – a contribution to integrated risk management
The FOEN produces a new forecast every day and uses graphics, maps and bulletins on the hydrological situation in Switzerland to provide information. In flood situations forecasts are updated several times a day.
The model results are issued in the form of graphics without comments showing the measured data (hourly averages) for the last few hours and the forecasts of hourly averages for the next three days.
The hydrological bulletin
A hydrological bulletin is issued every Monday and Thursday. It describes the current hydrological situation, weather developments and hydrological forecasts for the next three days.
Flood alerts to the cantonal authorities
An alert is sent by the FOEN to the cantonal authorities via the National Emergency Operations Centre (NAZ) when the forecasting service expects the water level or the discharge on a watercourse to reach a hazard level of 2 or higher. The alert contains information on the hazard level, the stations or regions affected, the time of peak water level and its height.
Natural hazards bulletin
The national government’s natural hazards bulletin is posted on various platforms in addition to the alert. It is written jointly by the FOEN forecasting service, MeteoSwiss and the WSL Institute for Snow and Avalanche Research SLF and contains information on the current situation, meteorological predictions, hydrology, plus snow conditions and landslides if relevant. It is issued one hour after an alert is sent to the authorities, normally at 12:00 or 18:00.
Weekly forecast bulletin
The weekly forecast bulletin provides advance information about flood alerts from the federal government for the next five days. There are three categories of flood probability:
- Flood alert active (probability of over 70%)
- Flood alert probable (probability between 40%-70%)
- Flood alert possible (probability under 40%)
This bulletin is updated every day at 12 noon.
Contribution to integrated risk management
The FOEN is responsible for warning the authorities and the population of floods. By operating the hydrological forecasting service, the FOEN contributes to integrated risk management before and during an event. The activities of the forecasting service consist of:
- Updating the forecasts once or several times a day
- Updating the weekly forecast bulletin every day
- Issuing the federal natural hazards bulletin jointly with the government agencies affected
- Telephone advice to the cantonal authorities
2. Hydrological forecasts: who for?
Shipping companies, power plants and businesses with a high process water requirement need hydrological forecasts of discharges or water levels for their planning.
If there is a threat of floods, local residents, settlements, industrial plants, roads, railway lines and construction sites in or along the watercourse are at risk. Hydrological forecasts are necessary to allow the authorities responsible for flood protection to take emergency action in time.
The FOEN Hydrological Department produces hydrological forecasts for various stations in the basins of the Rhine, Rhone and soon also the Ticino. In future these forecasts will be provided for all the major Swiss rivers and the main tributaries from other countries.
In view of climate change, low water and drought forecasts will also be of interest in the future. These forecasts will be prepared in conjunction with the National Centre for Climate Services (NCCS).
3. How are the discharge and water level forecasts and alerts produced?
Every morning the forecasting team produces new discharge forecasts, interprets the prognoses and issues the forecasts. The graphic below and the accompanying text describe this process.
Collecting the necessary data in a database:
The FOEN forecasting centre collects all of the data required to produce the forecasts:
- Weather data from the MeteoSwiss SwissMetNet stations and stations in the cantons and neighbouring countries
- Data from precipitation radar to provide qualitative support for assessment of the current weather developments
- Lake and river water levels measured by the monitoring stations operated by the FOEN, the cantons and neighbouring countries
Checking and processing the data and lake outflows:
- The raw data must be checked for completeness and plausibility and corrected as necessary
- Data for entire basin areas must be extrapolated from the local weather data
- It is then decided whether lake outflows using the predefined regulation schedules can be adopted in unmodified form for the forecasting period or whether discussion with the cantons is necessary, particularly in a flood situation.
Generating the forecast:
- The forecasts of water levels and discharges are computed by the hydrological models at hourly increments. The FOEN operates the HBV, WASIM, PREVAH, LARSIM and RS3 models.
Interpretation and publication:
- The forecaster interprets the results from the hydrological forecast models
- They are agreed with other experts if necessary (e.g. MeteoSwiss, cantons, …)
- If appropriate, the alert data is sent to the cantons and the forecast and alert data is posted on the web platforms.
If a flood hazard exists, alerts are sent via the National Emergency Operations Centre (NAZ) to the cantonal authorities. The natural hazards alert bulletin giving further information is also posted on various platforms (see above). The alerts are based on interpretation of the forecasts.
Last modification 05.09.2016