Relative change in the river discharge for flood events that have a probability to occur once every hundred years between the scenario run (2071-2100) and the control run (1961-1990). Simulations with LISFLOOD model driven by HIRHAM – HadAM3H / HadCM3 and IPCC SRES scenario A2. Only rivers with a catchment area of 1000 km 2 or more are shown. Map elaboration by EC JRC/IES.
(Figure 8 in the Green Paper on Adaptation)
How the results have been computed
Flood generation is a highly non-linear process that depends on factors such as the intensity, volume and timing of precipitation, antecedent conditions of the river basin (for example, soil wetness, snow or ice cover), river morphology, land use, and flood control measures (for example, reservoirs and dykes).
We use a hydrological model to simulate the spatial and temporal patterns of water flow in large river basins in Europe. To this end, the model is driven by temperature, precipitation, solar and thermal radiation, humidity and wind speed from a regional climate model, and uses spatial information about the topography, soils and land cover in the river basin. The hydrological model was run using climate for the control period 1961-1990 and for the scenario period 2071-2100 according to the A2 greenhouse gas emission scenario of the IPCC. The map is derived from a comparison of the statistics of flood frequency and magnitude between the control and future period.
What does this map tell us about future floods in Europe?
The map presents, for European rivers with a catchment area larger than 1000 km2, the change in river discharge for a flood event that has a probability to occur once every hundred years. Where rivers are coloured in red, the 100-year flood event will become less severe. Rivers in blue are projected to see 100-year events that are more severe. From this map, it can be seen that, in general, extreme river flows will increase in large parts of Europe, except in northeastern parts of Europe, parts of Germany, as well as in the Lower Danube region. In the Iberian Peninsula, the pattern is mixed, but still several catchments will likely see an increase in extreme river flows, despite that the climate will get much drier and hotter in this region. In northeastern parts of Europe, the peak discharge usually occurs in spring, when the snow pack accumulated during the winter melts away. The decrease in extreme river discharge in these regions is likely due to higher temperatures causing a shorter snow season and less snow accumulation. A similar change can also be seen in some rivers draining from the Alps and the Carpathian Mountains. Sweden, where the pattern is more mixed, will see less snowmelt induced extreme river flows, but due to a large increase in mean precipitation, as well as in extreme precipitation, several regions in Sweden will still see an increase in extreme river flows.
The map is based on one emission scenario (IPCC SRES A2) and one climate model (HIRHAM, Danish Meteorolgical Institute). Hence, uncertainty due to emission scenario or climate model is neglected and the results presented here are conditional on the emission scenario and climate model chain used.