Mean discharge of the Etsch/Adige river

Background information

Average runoff is mainly influenced by precipitation. If it falls as snow, it contributes to runoff through snowmelt or stores the water in glaciers for the long term. Evaporation and crop transpiration remove water from the soil and water bodies and release it into the atmosphere. We influence the amount of water in a river by using it for drinking, industrial use and agricultural irrigation. If the watercourse is managed with reservoirs for hydroelectric power generation, this also changes the flow.

Description of the results

The discharge of a river varies greatly from year to year because it is influenced by precipitation. In the hydrological year 2000/2001, for example, a very high average discharge was recorded because large amounts of precipitation fell in the form of snow, particularly in the autumn of 2000, and this led to increased water flows during the snowmelt period in the spring of 2001. However, reliable trends can only be derived from long-term observations. In general, temperatures have risen sharply in recent decades, but average precipitation has not, although its variability has. Nevertheless, no trend can be discerned in the annual course of the average discharge of the Etsch/Adige river at the Branzoll/Bronzolo gauge, which represents almost the whole of South Tyrol. However, if the year is divided into summer and winter periods, clear seasonal trends become apparent.

In the summer half of the year, the trend is downward, with a decrease in runoff over 10 years of 2.9 m³/s, which is 1.5% less runoff over 10 years, but which is not statistically significant. It is likely that higher winter temperatures mean that less precipitation is stored as ice and snow and instead runs off directly as rain. This results in less ice and snow melting in summer. In addition, runoff is reduced in the summer months due to evaporation and irrigation as a result of higher temperatures and lower water volumes. If average runoff decreases and water temperature increases in summer, water quality and freshwater habitats may be adversely affected (1).

On the other hand, runoff in the winter half of the year has increased statistically significantly by 4.6 m³/s over 10 years, this corresponds to an increase in runoff of 5.4%. On average, the annual data show a tendency towards a decrease in precipitation. More precipitation falls as rain in winter and less as snow, with an increase in variability. Wet winters are interspersed with very dry winters, such as the extremely low precipitation in the winter of 2021 to 2022.

Precipitation in the Alpine region is shifting due to climate change. Higher temperatures could mean more water evaporates, less snow falls, snow melts earlier and glaciers shrink. This will lead to a change in the river regime, with reduced flows, especially in summer (2).

Method

The mean discharge is calculated in cubic meters per second (m³/s) and is derived from the measurement of the water level and velocity at different depths in the river.

In South Tyrol there are about 50 gauging stations for mean discharge. The Branzoll/Bronzolo gauge on the Etsch/Adige river was chosen for the mean discharge indicator because of its long-term data series and location. It is provided by the Civil Protection Agency of the Autonomous Province of Bolzano and records a very large proportion of the water flowing out of South Tyrol (3).

Sectors affected

• Agriculture

• Water management

• Flora and Fauna

• Renewable Energy

Related indicators

Further research at Eurac Research

·      AlpWater Institut für alpine Umwelt: https://www.eurac.edu/en/institutes-centers/institute-for-alpine-environment/projects/alpwater

·      EcoHydro Institut für alpine Umwelt: https://www.eurac.edu/en/institutes-centers/institute-for-alpine-environment/projects/ecohydro

·      ALFFA Institut für alpine Umwelt: https://www.eurac.edu/de/institutes-centers/institut-fuer-alpine-umwelt/projects/alffa 

·      ADO „Observatorium für Dürre in den Alpen“ Institut für Erdbeobachtung https://www.alpine-space.org/projects/ado/en/home

·      NEXOGENESIS Institut für Erdbeobachtung https://www.eurac.edu/de/institutes-centers/institut-fuer-erdbeobachtung/projects/nexogenesis

·      Eurac Research Magazine: https://www.eurac.edu/de/magazine/wenig-schnee-wenig-regen-und-zu-viel-warme

References

1.     Van Vliet Michelle T. H., Franssen Wietse H. P., Yearsley John R., Ludwig Fulco, Haddeland Ingjerd, Lettenmaier Dennis P., Kabat Pavel, 2013: Global river discharge and water temperature under climate change. Global Environmental Change 23:450-464 http://dx.doi.org/10.1016/j.gloenvcha.2012.11.002

2.     Mallucci S., Majone B., Bellin A., 2019: Detection and attribution of hydrological changes in a large Alpine river basin. Journal of Hydrology 575:1214-1229 https://doi.org/10.1016/j.jhydrol.2019.06.020

3.     Terzi, S., Sušnik, J., Schneiderbauer, S., Torresan, S.,  Critto, A., 2021. Stochastic system dynamics modelling for climate change water scarcity assessment of a reservoir in the Italian Alps. Nat Hazard Earth Sys 21, 3519–3537. https://doi.org/10.5194/nhess-21-3519-2021

Contact

Eurac Research: Giacomo Bertoldi, Institute for Alpine Environment

Data provided by: Amt für Hydrologie und Stauanlagen of the Autonomous Provice of Bolzano