Indicator Assessment

River flow

Indicator Assessment

Prod-ID: IND-103-en

Also known as: CLIM 016

Published 20 Dec 2016 Last modified 18 Nov 2021

11 min read

Topics: Climate change adaptation Water and marine environment

This page was archived on 18 Nov 2021 with reason: No more updates will be done

Available studies suggest that run-off in near-natural rivers during the period 1963–2000 increased in western and northern Europe, in particular in winter, and decreased in southern and parts of eastern Europe, in particular in summer. However, comprehensive observation data on river flows are not available across Europe.
Long-term trends in river flows due to climate change are difficult to detect because of substantial interannual and decadal variability, as well as modifications to natural water flows arising from water abstractions, morphological changes (such as man-made reservoirs) and land-use changes.
Climate change is projected to result in significant changes in the seasonality of river flows across Europe. Summer flows are projected to decrease in most of Europe, including in regions where annual flows are projected to increase. Where precipitation shifts from snow to rain, spring and summer peak flow will shift to earlier in the season.

Fig. 1: Model-based estimate of past change in annual river flows

Note: The pronounced dipole pattern found for the annual flow trends appears to reflect the wetting trend pattern of the winter period (ca. December to April) in the north and northwest and the widespread drying trend pattern from late winter to late summer (ca. February–August) in southern and parts of eastern Europe

Data source:

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Fig. 2: Projected change in seasonal streamflow for twelve rivers

Note: This figure shows the projected change in seasonal streamflow (averaged over seven days) for twelve rivers.

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Past trends

Human interventions in catchments, including water abstractions, river regulation and land-use change, have considerably altered river flow regimes in large parts of Europe, making it difficult to discern any climate-driven changes in river flow data. An inventory of river flows in Europe was produced by combining over 400 time series (from 1962 to 2004) of river catchments with near-natural flow conditions for Europe and an ensemble of eight large-scale hydrological models (for 1963–2000) [i]. According to this inventory, run-off showed positive trends in western and northern Europe and negative trends in southern and parts of eastern Europe (Figure 1). The European pattern of annual run-off trends modelled by the ensemble mean shows a regionally coherent picture. The areas where models disagreed on the trend direction were largely located in areas of weak trends, notably in the transition areas between regions with consistent negative and positive trends. The pattern of changes in regional high flows is very similar to the pattern of changes in annual flows, whereas summer low flows have also decreased in various regions where annual flows have increased. Overall, positive trends in annual stream flow appear to reflect the marked wetting trends of the winter months, whereas negative annual trends result primarily from a widespread decrease in stream flow in spring and summer months, consistent with a decrease in summer low flow in large parts of Europe. The model uncertainties were largest in complex terrain with high spatial variability and in snow-dominated regimes.

The magnitude of the observed seasonal changes clearly raises concerns for water resource management both today and in future decades. To date, however, despite the evidence of changes in the seasonality of flows, there is no conclusive evidence that low river flows have generally become more severe or frequent in Europe during recent decades [ii]. Whereas many studies detect significant hydrological changes in observed datasets, more scientific rigour is needed in the attribution of river flow changes, as these studies often fall short in proving and quantifying the relationship between these changes and potential drivers [iii].

Projections

Annual river flows are projected to decrease in southern and south-eastern Europe and increase in northern and north-eastern Europe [iv]. Changes are projected in the seasonality of river flows, with large differences across Europe. For most parts of Europe, the peak of the average daily flow at the end of the 21st century is projected to occur earlier in the year than currently [v]. In snow-dominated regions, such as the Alps, Scandinavia and parts of the Baltic, the reduction in winter retention as snow, earlier snowmelt and, in some cases, reduced summer precipitation are projected to lead to increases in river flows in winter and reductions in summer [vi]. Reductions of flow can be exacerbated by water abstractions, especially in summer when consumption is highest and input is typically low. These changes result in a further decrease of water availability in summer (see Figure 2) [vii].

[i] K. Stahl et al., ‘Filling the White Space on Maps of European Runoff Trends: Estimates from a Multi-Model Ensemble’,Hydrology and Earth System Sciences 16, no. 7 (11 July 2012): 2035–47, doi:10.5194/hess-16-2035-2012.

[ii] K. Stahl et al., ‘Streamflow Trends in Europe: Evidence from a Dataset of near-Natural Catchments’,Hydrology and Earth System Sciences 14, no. 12 (1 December 2010): 2367–82, doi:10.5194/hess-14-2367-2010; Stahl et al., ‘Filling the White Space on Maps of European Runoff Trends’.

[iii] B. Merz et al., ‘HESS Opinions “More Efforts and Scientific Rigour Are Needed to Attribute Trends in Flood Time Series”’,Hydrology and Earth System Sciences 16, no. 5 (11 May 2012): 1379–87, doi:10.5194/hess-16-1379-2012.

[iv] Rodrigo Rojas et al., ‘Assessment of Future Flood Hazard in Europe Using a Large Ensemble of Bias Corrected Regional Climate Simulations’,Journal of Geophysical Research 117 (2012): D17109, doi:10.1029/2012JD017461; L. Alfieri et al., ‘Global Warming Increases the Frequency of River Floods in Europe’,Hydrology and Earth System Sciences 19, no. 5 (11 May 2015): 2247–60, doi:10.5194/hess-19-2247-2015.

[v] Michelle T. H. van Vliet et al., ‘Global River Discharge and Water Temperature under Climate Change’,Global Environmental Change 23, no. 2 (April 2013): 450–64, doi:10.1016/j.gloenvcha.2012.11.002; G. Forzieri et al., ‘Ensemble Projections of Future Streamflow Droughts in Europe’,Hydrology and Earth System Sciences 18, no. 1 (9 January 2014): 85–108, doi:10.5194/hess-18-85-2014.

[vi] Alfieri et al., ‘Global Warming Increases the Frequency of River Floods in Europe’.

[vii] Forzieri et al., ‘Ensemble Projections of Future Streamflow Droughts in Europe’.

Supporting information

Indicator definition

Model-based estimate of past change in annual river flows

Projected change in seasonal river flow for 12 rivers

Units

percentage change (%)
cubic metres per second (m³/s)

Rationale

Justification for indicator selection

Annual average river flows are one of the elements that affect freshwater availability in a river basin, in addition to groundwater sources, lakes or artificial water storage facilities. Variations in river flows are determined mainly by the seasonality of precipitation and temperature, as well as by catchment characteristics such as geology, soil and land cover. Changes in temperature and precipitation patterns due to climate change modify the annual water budget of river basins and the timing and seasonality of river flows. The consequent changes in water availability may adversely affect ecosystems and several socio-economic sectors, including abstraction for drinking water, agriculture, industry, energy production and navigation. Extreme dry periods with low river flow events can have considerable economic, societal and environmental impacts.

Scientific references

IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
IPCC, 2014: Europe. Kovats, R.S., R. Valentini, L.M. Bouwer, E. Georgopoulou, D. Jacob, E. Martin, M. Rounsevell, and J.-F. Soussana, 2014: Europe. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1267-1326.

Policy context and targets

Context description

In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe.

One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.

Further objectives include Promoting adaptation in key vulnerablesectors through climate-proofing EU sector policies and Promoting action by Member States. Most EU Member States have already adopted national adaptation strategies and many have also prepared action plans on climate change adaptation. The EC also supports adaptation in cities through the Covenant of Mayors for Climate and Energy initiative.

In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.

In November 2013, the European Parliament and the European Council adopted the 7^th EU Environment Action Programme (7^th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7^th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7^th EAP refer to climate change adaptation.

Targets

No targets have been specified.

Methodology

Methodology for indicator calculation

An inventory of river flows in Europe was produced by combining over 400 time series (from 1962 to 2004) of river catchments with near-natural flow conditions for Europe and an ensemble of eight large-scale hydrological models.

The projected river flow is based on a set of 12 climate simulations from the ENSEMBLES project, covering the period up to 2100. The effects of potential changes in future water consumption were included using the WaterGAP3 model.

Methodology for gap filling

Not applicable

Methodology references

Stahl et al. (2012): 'Filling the white space on maps of European runoff trends: estimates from a multi-model ensemble. Stahl, K., Tallaksen, L. M., Hannaford, J. and van Lanen, H. A. J., 2012, 'Filling the white space on maps of European runoff trends: estimates from a multi-model ensemble', Hydrology and Earth System Sciences 16(7), 2035–2047 (DOI: 10.5194/hess-16-2035-2012).
Forzieri et al. (2014): 'Ensemble projections of future streamflow droughts in Europe. Forzieri, G., Feyen, L., Rojas, R., Flörke, M., Wimmer, F. and Bianchi, A., 2014, 'Ensemble projections of future streamflow droughts in Europe', Hydrology and Earth System Sciences 18(1), 85–108 (DOI: 10.5194/hess-18-85-2014).

Uncertainties

Methodology uncertainty

Not applicable

Data sets uncertainty

River flow and water level data are influenced by rainfall run-off and by hydromorphological changes of the river bed, e.g. through river engineering. Furthermore, homogeneous time series are generally shorter than those for meteorological data. Therefore, substantially more time may be required before statistically significant changes in hydrological variables can be observed, especially with respect to extreme and exceptional events (floods and droughts).

Rationale uncertainty

No uncertainty has been specified

Data sources

Filling the white space on maps of European runoff trends: estimates from a multi-model ensemble
provided by University of Freiburg
Ensemble projections of future streamflow droughts in Europe
provided by

Permalinks

Older versions

Geographic coverage

Temporal coverage

For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/river-flow-3/assessment or scan the QR code.

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