River flow

Modelled change in annual river flow between 1971-1998 and 1900-1970

Note: The map is based on an ensemble of 12 climate models and validated against observed river flows.

Data source:

• Geophysical Fluid Dynamics Laboratory (GFDL) provided by National Oceanic and Atmospheric Administration (NOAA)

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Projected change in mean seasonal and annual river flow between 2071-2100 and the reference period 1961-1990

Note: Simulations with LISFLOOD driven by HIRHAM HadAM3H/HadCM3 based on IPCC SRES scenario A2.

Data source:

Dankers, R.; Feyen, L., 2008a. Climate change impacts on river flow in Europe (manuscript in preparation).

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Projected change in daily average river flow for four rivers

Note: Projected river flow 2071-2100 (green line) and the observed river flow 1961-1990 (orange line)

Data source:

Dankers, R.; Feyen, L., 2008a. Climate change impacts on river flow in Europe (manuscript in preparation).

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Past trends

In accordance with the observed changes in precipitation and temperature, there is some evidence for climate-induced changes in annual river flow, as well as in the seasonality of flow, in Europe during the 20th century. However, anthropogenic interventions in the catchment, such as groundwater abstraction, irrigation, river regulation, land-use changes and urbanisation, have considerably altered river flow regimes in large parts of Europe, confounding climate change detection studies.
In northern parts of Europe, mean annual river flow has in general increased (Lindstrom and Bergstrom, 2004; Milly et al., 2005). Increases occurred mainly in winter and spring (Hisdal et al., 2007), probably caused by a general temperature increase during recent decades in combination with increased winter precipitation in the northern regions. Significant increases in river flow have also been observed in Scotland at one third of the river gauging stations in the past three decades (Werritty, 2002), as well as in winter and autumn in western Britain, consistent with recent increases in winter rainfall and a positive North Atlantic Oscillation index (Dixon et al., 2006). However, some of these changes could be part of natural variability (Wade et al., 2005). In western and central Europe, annual and monthly mean river flow series appear to have been stationary over the 20th century (Wang et al., 2005). In mountainous regions of central Europe, however, the main identified trends are an increase in annual river flow due to increases in winter, spring and autumn river flow. In summer, both upward and downward trends have been detected (Birsan et al., 2005). In southern parts of Europe, a slightly decreasing trend in annual river flow has been observed (Milly et al., 2005).

Projections

 Annual river flow is projected to decrease in southern and south-eastern Europe and increase in northern and north-eastern Europe (Arnell, 2004; Milly et al., 2005; Alcamo et al., 2007). Strong changes are also projected in the seasonality of river flows, with large differences across Europe. Winter and spring river flows are projected to increase in most parts of Europe, except for the most southern and south-eastern regions. In summer and autumn, river flows are projected to decrease in most of Europe, except for northern and north-eastern regions where autumn flows are projected to increase (Dankers and Feyen, 2008a). In snow-dominated regions, such as the Alps, Scandinavia and the Baltic, the fall in winter retention as snow, earlier snowmelt and reduced summer precipitation will reduce river flows in summer (Andreasson, et al., 2004; Jasper et al., 2004; Barnett et al., 2005), when demand is typically highest.