The water balance includes the main components of the water cycle. The FOEN calculates the water balance for Switzerland and its large river basins every year.
The water balance includes the components of the water cycle relevant to a specific analysis area. The components are quantified by simple balance equations. The level of detail is dependent on the size of the basin under consideration. The classic water balance equation is often sufficient for large river basins:
Precipitation = runoff + evaporation +/- storage changes
More detailed consideration may be appropriate for smaller basins. As an example, evaporation is divided into interception evaporation, evaporation and transpiration or runoff into surface runoff, interflow and baseflow.
Swiss water balance
The FOEN calculates the water balance for political Switzerland and for the large river basins every year. The boundaries of the political entities often differ from the natural boundaries of the catchment areas. Where this is the case, the major feeders into the basin must be determined separately.
Comparison with the long-term average
The data for each separate year is only informative if it can be compared with the long-term average. Periods called standard periods are used for comparison in both meteorology and hydrology. The current standard period is from 1981 to 2010.
In addition to the data processed annually, the water balance analysis includes the water reserves. They refer to the total water volume stored. This represents a potential reserve and includes existing water resources which are stored but are not necessarily technically, ecologically, economically or legally usable.
The water reserves of Switzerland are approximately 340 km3. In the case of the lakes, this figure only includes the Swiss portion of Lake Constance and Lake Geneva.
|Natural lakes > 100 million m3, Swiss portion||130|
Last modification 19.06.2020