Swiss water balance

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 

Die Komponenten des Wasserkreislaufs
The components of the water cycle.

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.

Data (mm / year) for Swiss water balance for the calendar year 2016 and in brackets in italics for the 1981–2010 standard period. The graphic shows political (grey) and hydrological (light grey) Switzerland.

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.

Natural water balance for the whole of Switzerland and important large catchment areas for 2016 and the standard period 1981–2010 (mm / year). P: precipitation; R: runoff; E: evaporation; dS: storage change.

Water reserves

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 le-gally usable. According to the FOEN, of the total groundwater volume of some 150 km3, about 10% (ca. 18 km3) is replenished annually and can be sustainably used.

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.

Description km3 
Natural lakes > 100 million m3, Swiss portion 130 
Glaciers 57 
Groundwater 150 


Water reserves of Switzerland (Source: BAFU, VAW [Laboratory of Hydraulics, Hydrology and Glaciology])

Further informations

Last modification 12.09.2018

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