Annual precipitation: the average amount of precipitation that falls in a particular place each year. It is usually expressed in millimeters. On the Central Plateau, total annual precipitation is about 1000 mm. This means that a one-meter deep (= 1000 liters of water per m2) layer of water would cover the region if no runoff or evaporation was present.

Aquifer: permeable body of rock, often with very small cavities (pores), that can store groundwater.

Black water: volumes of polluted water no longer usable as drinking water.

Blue water: unpolluted water that runs off into streams and rivers or resides in lakes and groundwater.

Catchment area: closed hydrologic unit in which the water balance is considered. Every drop of water that falls on this surface flows away under the force of gravity, assuming it does not evaporate or get stored as snow or ice, or in groundwater or lakes. If the discharge of a river is measured at a location (e.g., the Aare River in Bern), the catchment area comprises the area from which rainfall sooner or later runs off.

Discharge: the volume of water that flows through a given cross section per second (in m3 per second).

Discharge regime: describes the average flow variation of a stream or river over time. The discharge regime is closely related to seasonal changes in climate.

Drinking water: clean, potable water that is treated as needed and conducted through public lines to households and other users.

Ecomorphology: οἶκος: house or household, μορφή [morphé]: shape or form and λόγος: the doctrine. Thus, ecomorphology describes the science of the structural nature of a body of water and its shore area, as well as its interactions with plants and animals. Sections of a river are classified depending on the water depth and velocity (e.g., pool, riffle, glide and runner).

Eutrophication: if large amounts of nutrients (often nitrate or phosphate from fertilizer and sewage) enter into a body of water, algae can reproduce very quickly and lower the oxygen content of the water in such a way that biodiversity (especially for fish) decreases. Some of the smaller lakes in intensively used agricultural areas (e.g., Hallwilersee) must be artificially oxygenated to prevent eutrophication.

Evapotranspiration: in the environment, water evaporates to form water vapor (an invisible gas), for example over water bodies such as seas, lakes and rivers. The water that is present in the soil (soil moisture) can also evaporate. In addition, plants “sweat” during photosynthesis, a process known as “transpiration”. This invisible water vapor can re-condensate into water droplets if the air cools sufficiently, forming fog or clouds.

Groundwater: water that is located underground (such as in the aquifers in the karst regions or in the Central Plateau). Most of the water (approximately 80%) is found in karst areas (Alps, Jura Mountains) and at depths between 100 and 1000 meters. Renewable groundwater is the proportion of groundwater that can be sustainably used; that is, without affecting the quantity or quality. This proportion varies by region (on average, 10% of the available groundwater) and depends mainly on the underlying geology and the presence of watercourses.

Gray water (or greywater): slightly polluted water (without fecal contamination) that can be reused directly or indirecty (treatment in short circuits without passing through a purification plant).

Green water: rainwater stored in the soil that is used by plants.

Hydropeaking: Rapid changes in flow below hydropower plants result from peaking operations, where water is typically stored in a reservoir at night and released through turbines to satisfy increased electrical demand during the day. This artificial increase or decrease in discharge is known as “hydropeaking”, and poses a problem for downstream ecosystems due to the rapidly changing volume, flow rate and temperature of the water.

Intensity (of precipitation): precipitation (rain, snow, hail, etc.) can fall with varying levels of strength, from fine drizzle to heavy rain showers or thunderstorms. The intensity of precipitation depends on the type of weather and on the elevation. A unit commonly used to measure the intensity of precipitation is the number of liters of water that falls on one square meter in 10 minutes, one hour, or one day.

Interception: the fraction of precipitation that does not fall directly on the ground, but is caught by vegetation (leaves, branches, trunks) and is therefore either delayed in reaching the ground or directly re-evaporated.

Irrigation canals: historical irrigation canals (“Suonen”) in Canton Valais, the driest region of Switzerland. These canals bring water from mountain streams – in a rather adventurous way – to the dry pastures, fields, vineyards and orchards below.

Moisture sources: areas from which large amounts of water evaporate into the atmosphere and form clouds that later rain out over Switzerland.

Pardé-coefficient: this coefficient is named after a famous French hydrologist and gives a normalized discharge value (ratio of the average monthly discharge to mean annual discharge). The coefficient allows the comparison of flow regimes from different catchment areas.

Precipitation: see annual precipitation or intensity (of precipitation).

Pumped storage power plant: in hydroelectric power plants, there is a difference between diverted flow and storage power plants. Numerous diverted flow power plants are located along our rivers because they are enabled by the river gradient. In contrast, storage power plants are situated below reservoirs (artificial lakes), and work due to the change in height between the dam and the power plant below. If water can be pumped back into the reservoir, the system is called a pumped storage power plant

Reservoir: in the hydrological system, a unit of water can be “removed” from the water cycle for a short (snow cover, soil moisture, groundwater) or long (lakes, groundwater, glaciers) period of time before re-entering the water cycle.

Restoration (or renaturation): Switzerland’s watercourses have been strongly modified (straightened, channeled, culverted), which has affected the natural diversity of flora (e.g., rare plants) and fauna (e.g., fish) in and along rivers. These modifications are often done as flood protection measures. However, it is now known that these measures often increase the risk of flooding because water can travel much faster in a straight channel. Flood protection can be combined with restoration by allowing rivers more space to meander, creating a win-win situation for both humans and nature.

Specific discharge: This volume corresponds to the discharge per unit area of the catchment. It is typically expressed in liters per second and km2.

Surface runoff: the fraction of precipitation that directly enters stream channels as a function of gravity.

Surface water: natural and artificial streams, rivers and lakes.

Variability (of precipitation or runoff): annual precipitation varies from year to year and is therefore usually calculated for a period of 30 years. The variability represents the scatter of the annual precipitation within this period (e.g., the difference between the driest year and the year with the most precipitation). This analysis can also be performed for the discharge of a watercourse.

Virtual water: is the amount of water necessary to produce products abroad (agricultural products, processing of raw materials, etc.) that are then consumed in Switzerland. A distinction is made between green, blue and gray water.

Water balance: Discharge = Precipitation minus Evapotranspiration minus the change in the reservoir. The water balance formula represents a highly simplified description (mean) of the hydrological system of a closed basin.

Water consumption: refers to the quantities of (drinking) water that are evaporated, lost or contaminated (gray water) during consumption.

Watercourses: streams, rivers.

Water supply: Man has no influence on the amount of precipitation that falls in different regions of the world. We are the mercy of nature. A part of the precipitation evaporates and some is cached (e.g., as snow). The rest is the water supply, which flows into streams and rivers and feeds lakes and groundwater.

Water use: is mainly used to describe quantities of water that are used to generate hydroelectric power or for cooling before being returned (clean) to the environment.

Water resources: describe the quantity of water that can be used sustainably and is stored in the meantime (e.g., as rain water, snow and glacier melt, in rivers and streams, or in groundwater).


International Glossary of WMO