Impact of climate change on the water balance

Climate change affects the entire water cycle. Surface and underground waters are equally exposed to changes in water quantity and quality. This has direct repercussions on hydropower, water supplies, urban drainage, navigation, agriculture, ecology and water-induced natural hazards.

Links befindet sich schneebedecktes Gras mit kahlen Bäumen. Rechts fliesst ein Fluss durch eine sonnige Winterlandschaft.

The “Climate Change and Hydrology in Switzerland” (CCHydro) project initiated by the Federal Office for the Environment (FOEN) examined the repercussions of climate change on the Swiss water balance. For the first time, scientifically reliable information could be given on the changes in the Swiss water balance by the end of the 21st century.

EHS_Module_D

Auswirkungen der Klimaänderung auf Wasserressourcen und Gewässer (PDF, 4 MB, 25.10.2018)

Synthesebericht zum Projekt "Klimaänderung und Hydrologie in der Schweiz" (CCHydro)

In order to improve understanding of the hydrological process and update the knowledge base, the project “Climate Change and its Consequences on Hydrology in Switzerland” (Hydro-CH2018) was initiated. It represents one of the core topics of the newly formed Swiss Government network National Centre for Climate Services (NCCS).

New hydrological scenarios will be created on the basis of the updated 2018 climate scenarios. These will focus mainly on the areas of extreme events (floods and low water), natural and man-made reservoirs as well as surface water temperatures and ecology. Climate services for water will also be developed and made available. They give scientifically-based information and data on the past, present and future water balance. They will help authorities, policy makers, businesses and society to reduce climate-induced risks. 

Discharge regime

In the alpine region, the rise in temperature is the most important factor influencing the seasonal changes in discharges: The snow line is rising and winter snow reserves and glacier volumes and areas are shrinking.

The seasonal discharge distribution (regime) will change throughout almost the whole of Switzerland. Discharges will increase considerably in many regions in winter but will decrease in summer. Regimes that are largely unknown today will occur, with a seasonal maximum discharge in winter and a very low minimum in August. The overall total annual discharges in Switzerland will change relatively little in the near future (to 2035) and will even increase temporarily in glaciated regions. In the more distant future (2085), total discharges will generally decrease slightly.

Regionen mit ähnlichen Veränderungen der saisonalen Abflussverhältnisse auf Grund des Klimawandels. Es werden die Mittelwerte der beiden Zeitfenster 2020 – 2049 und 2070 – 2099 betrachtet. Die Berechnungen gehen vom Szenario mit mittleren Emissionen SRES-A1B aus. Alle Regionen zeigen eine Zunahme der Abflüsse im Winter und eine Abnahme im Sommer, wobei Zeitpunkt und Ausmass der Veränderungen je nach Region variieren. Besonders betroffen ist der Alpenraum (Blautöne), weniger stark betroffen sind das Mittelland, der Jura, die Voralpen sowie die sehr hoch gelegenen Gebiete im südlichen Wallis (hellbraun). (Quelle: Köplin et al. 2012; Rössler et al. 2014)

Cryosphere

By the end of this century the area of glaciation in the Swiss Alps will have been reduced even further. Glaciers will only be found in the high-elevation regions of the Bernese and Valais Alps. Depending on the model and climate scenario used, a loss of 60 to 80% of the current Swiss glacier area can be assumed.

By the end of the century the greatest volume of ice will be located in the Rhone basin (Valais), where some 80% of the Swiss glacier volume is currently found. In contrast, the Rhine basin will lose all its glaciers apart from a few stretches of ice in the Bernese Oberland. The Engadine and Ticino will be totally ice free by the end of the century.
 

Changes in the water volumes stored in Swiss glaciers (Engadin & Ticino, Rhine and Rhone catchment areas) since the end of the Little Ice Age. The values since the end of the Little Ice Age are estimated (with 20% to 30% uncertainty) and simulated until 2100.

Snow is an important water resource in Switzerland. In alpine regions snow melt is the principal component of the discharge for a third of the year (March to June). The snow cover responds very sensitively to changes in temperature and precipitation, making it a good indicator of changes in climate. Due to the increase in temperature, a higher proportion of the precipitation is already falling as rain rather than snow, particularly at lower levels. Snow melt is also occurring earlier in the season due to the higher temperatures. This is shortening the period of snow cover and reducing the quantity of water stored temporarily in the snow. This trend will further intensify by the end of the century.

Extreme events

A warming atmosphere can hold more water vapour, leading to a greater potential for heavy precipitation. Due to rising temperatures, more precipitation also falls as rain rather than snow (particularly in spring and autumn in alpine and prealpine catchments and also in summer in very high elevation regions). Therefore an increase in the frequency and intensity of medium and large flood events and an extension of the potential flood period in spring and late autumn can be expected. It is not known how the atmospheric circulation and therefore the frequency of weather conditions triggering floods will develop due to climate change.

At the same time, the increase in hot and dry summers, more frequent and longer lasting low water periods can be expected, especially in late summer.
 

Emme
© Esther Scheidegger, BAFU

Soil moisture and evaporation

The CH2018 climate projections anticipate hotter and drier summers with longer and more frequent droughts for Switzerland. More water can also evaporate at higher temperatures. All these factors will lead to a reduction in soil moisture in summer. Whether or not more water will actually be lost to evaporation in a future climate will depend on how much is still available in the soil to evaporate and what the water requirement of vegetation will be. Adaptations in agriculture and forestry (e.g. climate compatible crops, irrigation) will also be necessary in Switzerland.

Nahaufnahme einer sumpfigen Wiese.
© BAFU

Water temperature, quality and ecology

Increasing air temperatures, the introduction of warm water from building cooling and wastewater treatment systems and the lack of shade-giving bank vegetation have allowed the water temperatures of many surface waters to rise significantly over recent decades.

Higher water temperatures result in less dissolved oxygen in the water. Bioactivity also increases causing oxygen demand to increase. In addition, diseases which are a health hazard for aquatic organisms spread more widely in warmer water. Lower water levels in the summer months will cause further increases in water temperature and endanger the survival of some organisms. Furthermore, if discharges are low, wastewater is less well diluted and water quality suffers. 

publikation-entwicklung-wassertemperatur-2017-de.PNG
Changes in water temperatures from 1954 to 2017 in selected Swiss rivers. Rolling averages (over 7 years) are shown as lines and the last four annual means as points or crosses (air).

Groundwater

The aquifers of the Jura, the Central Plateau and the Prealps are recharged by rain and snow melt. It can be assumed that they will fill in winter and will empty in spring due to the snow melt deficit. Groundwater recharge in alpine river valley gravels will also reduce in line with the decreased snow and glacier melt in summer. During the more frequent and longer periods of drought forecast by the climate scenarios, groundwater exfiltration into the rivers is likely to increase. Changes in groundwater recharge will affect groundwater temperature as well as its quantity. A rise in groundwater temperature will therefore be observed in the aquifers fed by river water infiltration, and also in urban areas, e.g. due to heat input from building cooling systems. Rising groundwater temperatures may lead to an increase in microbial activity and a fall in the oxygen concentration and in extreme cases iron and manganese precipitation.

Spiegelung eines Baumes im Grundwasser in Bad Zurzach.
© BAFU

Sediment transport

An increase in heavy precipitation, thawing of the permafrost and melting of glaciers may lead to more erosion, landslides and rockfalls. More material will then be available in the water for sediment transport. Higher sediment transport changes the discharge characteristics and channel morphology. This can have negative consequences for flood protection, restrict the output of hydropower plants and harm the water ecology.

Hochwasser am 24.08.2005 im Lütschental aus der Vogelperspektive.
© BAFU

Further information

Last modification 08.11.2018

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Hydrology Division

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Priority themes: Hydrological principles of climate change

The core topic of the NCCS Hydro-CH2018 focusses on the water resources and their future development. The objective is to supply the necessary fundamental hydrological principles for adaptation.

https://www.nccs.admin.ch/content/nccs/en/home/sektoren/wasserwirtschaft/auswirkungen-auf-den-wasserhaushalt.html