Precipitation extremes in Europe (CLIM 004) - Assessment published Sep 2008

Key policy question: .

Changes in the contribution of heavy rainfall to total precipitation 1961-2006

Note: The map shows changes in the contribution of heavy rainfall to total precipitation

Data source:

Dataportal at KNMI and ENSEMBLES gridded dataset

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Percentage of Europe experiencing moderate drought conditions during the 20th century

Note: Expressed as standardized precipitation indices (SPI) for time scales of 12 months

Data source:

Lloyd-Hughes, B. and Saunders, M. A., 2002. A drought climatology for Europe. International Journal of Climatology 22: 1571-1592.

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Simulated land average maximum 5-day total precipitation for different European regions (1860-2100)

Note: The 20th century (black), models simulations for IPCC SRES intermediate A1B (orange) and low B1 (green) emission scenarios

Data source:

Sillmann, J. and Roeckner, E., 2008. Indices for extreme events in projections of anthropogenic climate change. Climatic Change 86 (12): 83-104.

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Simulated land average maximum number of consecutive dry days for different European regions (1860-2100)

Note: The 20th century (black), models simulations for IPCC SRES intermediate A1B (orange) and low B1 (green) emission scenarios

Data source:

Sillmann, J. and Roeckner, E., 2008. Indices for extreme events in projections of anthropogenic climate change. Climatic Change 86 (12): 83-104.

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Key assessment

Past trends

The number of extreme precipitation events has increased over most of the European land area, linked to warming and increases of atmospheric water vapour. For Europe as a whole, also the intensity of extreme precipitation such as heavy rain has increased in the past 30 years, even for areas with a decrease in mean precipitation, such as central Europe and the Mediterranean. In particular, the contribution of heavy rain to total precipitation has increased (Figure 1).
The proportion of Europe that has experienced extreme and/or moderate meteorological drought conditions did not change significantly during the 20th century (Figure 2) (Lloyd-Hughes and Saunders, 2002). Some drying trends were observed over central and eastern Europe, and western Russia. Similar, some trends were observed in winter/spring. Summer droughts showed no statistically significant trends in the period 1901-2002 (Robock et al., 2005; van der Schrier et al., 2006).

Projections

For Europe as whole it is likely (66 % probability) that heavy precipitation events will continue to become more frequent (IPCC, 2007a). In summer, the frequency of wet days is projected to decrease, but the intensity of extreme rain showers may increase. In addition, the frequency of several-day precipitation episodes is projected to increase. Geographically, there is considerable regional differentiation in the projections. Extreme precipitation events are projected to increase by 17 % in northern and 13 % in central Europe during the 21st century, with no changes projected in southern Europe (for the ECHAM 4 climate model, A1B scenario, Figure 3, Sillmann and Roeckner, 2008).
The combination of higher temperatures and reduced mean summer precipitation is expected to enhance the frequency and intensity of droughts across Europe. This can be illustrated, for example, by the projected number of consecutive dry days, defined as days with precipitation below 1 mm (Figure 4). In southern Europe, the maximum number of these days is projected to increase substantially during the 21st century. The longest dry period within a year may be prolonged here by one month at the end of 21st century. In central Europe, prolongation of longest dry period is by one week, and no prolongation is projected for northern Europe. Thus regions in Europe that are now dry are projected to become even more vulnerable.