Climate change and hydrology

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 and water-related natural hazards.

The “Climate Change and Hydrology in Switzerland“ (CCHydro) project initiated by the Federal Office of 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.

Effects of climate change on water resources and watercourses

Cover Effects of climate change on water resources and watercourses

Synthesis report on the “Climate Change and Hydrology in Switzerland” (CCHydro) project. 2012

Hydro-CH2018 project “Climate Change and its Consequences on Hydrology in Switzerland”

In order to improve understanding of the hydrological process, 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. It 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-related risks.

Changes in discharge conditions

In the alpine region, the rise in temperature is the most important factor influencing the seasonal changes in discharges: The snowfall limit 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.

Groundwater also affected

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.

More 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.

Retreat of the glaciers

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 (Rhone and Rhine catchment areas, Engadin and Ticino) 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.

Water temperatures and ecology

Rising 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, some diseases 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.

Changes in water temperatures
Changes in water temperatures from 1954 to 2015 in selected Swiss rivers. Rolling averages (over 7 years) are shown as lines and the last four annual means as points or crosses (air).

Local and regional bottlenecks in the water balance

Switzerland is Europe’s water reservoir and will remain so overall for the foreseeable future. In future the climate-related changes in the supply of groundwater and surface waters will increasingly create temporary local and regional bottlenecks which will require water management adjustments. As the future European climate turns warmer and drier, the reservoir function of Switzerland will become even more important.

Further information

Last modification 30.06.2015

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