The flood alert map shows the current flood danger level (1 to 5) for all and for the regions in relation to small and medium-sized rivers.

The rivers of national interest are divided into individual stretches of river, each of which has a defined discharge gauging station. The forecast is based on a hydrological model and various weather models. Depending on how the forecasters assess and interpret the models, individual stretches of river and lakes are colour-coded by danger level. If necessary, the FOEN forecasters may request more detailed information on weather developments and the status of snow cover from MeteoSwiss and/or the WSL Institute for Snow and Avalanche Research (SLF).

The FOEN also issues alerts and information when a strong increase in discharge is expected locally on small and medium-sized rivers. In such cases – especially during thunderstorms with heavy rainfall – it is not possible to predict precisely which water bodies will be affected. Therefore, the regions likely to be affected are marked on the flood alert map. There are only three danger levels for small and medium-sized rivers due to the greater uncertainties involved: no or minor danger (green), moderate flood danger (yellow) and high flood danger (red).

Rivers and lakes of Swiss national interest are:

• Rivers and lakes along which high potential for damage exists.
• Main rivers which flow through several cantons or international rivers and lakes bordered by several cantons or forming a frontier with neighbouring countries.
• Rivers which have had their course altered in major historical correction projects with significant involvement by the Confederation, the long-term effects of which are to be evaluated by regular surveys.
• Rivers which are having their course altered under major current flood protection projects with significant involvement by the Confederation, the effects of which are to be assessed by regular surveys.
• Rivers where there are extensive floodplains of national importance.
• Tributaries which have a water and bedload carrying capacity or input (flow rate, bedload supply) which is of crucial importance for the main river system.

The 5 flood danger levels

Hydrological forecasts: Cooperation with expert national and international services