Precipitation extremes (CLIM 004) - Assessment published Nov 2012

Key policy question: What is the trend in the length of dry and wet periods, and in heavy precipitation events across Europe?

Trends in consecutive dry days and consecutive wet days

Note: High confidence in a long-term trend is shown by a black dot (if the 5th to 95th percentile slopes are of the same sign). Boxes which have a thick outline contain at least three stations. Area averaged annual time series of percentage changes and trend lines are shown below each map for one area in northern Europe (blue line, 5.6 to 16.9 °E and 56.2 to 66.2 °N) and one in south-western Europe (red line, 350.6 to 1.9 °E and 36.2 to 43.7 °N).

Data source:

• ENSEMBLES FP6 project provided by ENSEMBLE FP6 project

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Projected changes in 20-year maximum precipitation in summer and winter

Note: Projected changes in 20-year maximum daily precipitation in summer (left) and winter (right) from 1961–1990 to 2071–2100 based on the ensemble mean using a regional climate model (RCM) nested in 6 general circulation model (GCMs). Changes that approximately lie outside of ± 10 % for the ensemble average are significant at the 10 % significance level.

Data source:

• Evaluation and future projections of temperature, precipitation and wind extremes over Europe in an ensemble of regional climate simulations provided by Swedish meteorological and hydrologiska insitute (SMHI)

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Key assessment

Past trends

Observational records do not indicate widespread significant trends in either the number of consecutive wet days (indicating flood risks) or dry days (indicating drought risks) across Europe (Figure 1). Some changes in these variables have been observed across Europe but most of them are not statistically significant due to large natural variability. Interestingly, parts of north-western and north-eastern Europe show significant increasing trends in both the number of wet days and dry days. The proportion of Europe that has experienced extreme or moderate meteorological drought conditions did not change significantly during the 20th century [1]. Summer droughts have also shown no statistically significant trend during the period 1901–2002 [2].

Projections

Model-based projections for the 21st century show a reduction in the contribution of low rainfall days to total annual precipitation, and an increase in the contribution of high rainfall days in most parts of Europe, with the exception of the Iberian Peninsula and Mediterranean regions [3]. The recurrence time of intense precipitation is reduced from 20 years in the 1961–1990 periods to 6–10 years in the 2071–2100 period over northern and eastern central Europe in summer (Figure 2 left) and to 2–4 years in Scandinavia in winter (Figure 2 right) [4].

Extreme precipitation events are likely to become more frequent in Europe [5]. Changes in extreme precipitation depend on the region, with a high confidence of increased extreme precipitation in northern, Atlantic (all seasons) and central Europe (except in summer) [6]. Future projections are inconsistent in southern Europe (all seasons) [7]. The number of consecutive dry days is projected to increase significantly in southern and central Europe, in particular in summer, and to decrease in northern Europe, in particular in winter [8].

 [1] B. Lloyd-Hughes and M. A. Saunders, “A Drought Climatology for Europe,” International Journal of Climatology 22 (2002): 1571–1592, doi:10.1002/joc.846.

[2] A. Robock et al., “Forty-five Years of Observed Soil Moisture in the Ukraine: No Summer Desiccation (yet),” Geophysical Research Letters 32 (2005): L03401, doi:10.1029/2004GL021914.

[3] F Boberg et al., “Improved Confidence in Climate Change Projections of Precipitation Further Evaluated Using Daily Statistics from ENSEMBLES Models,” Climate Dynamics 35 (2009): 1509–1520, doi:10.1007/s00382-009-0683-8.

[4] J. E. Haugen and T. Iversen, “Response in Extremes of Daily Precipitation and Wind from a Downscaled Multi-model Ensemble of Anthropogenic Global Climate Change Scenarios,” Tellus Series A – Dynamic Meteorology and Oceanography 60, no. 3 (2008): 411–426; G Nikulin et al., “Evaluation and Future Projections of Temperature, Precipitation and Wind Extremes over Europe in an Ensemble of Regional Climate Simulations,” Tellus Series A 64 (2011): 41–55, doi:10.1111/j.1600-0870.2010.00466.x; S. I. Seneviratne et al., “Changes in Climate Extremes and Their Impacts on the Natural Physical Environment,” in Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC) (Cambridge: Cambridge University Press, 2012), pp. 109–230, http://ipcc-wg2.gov/SREX/contributors/chapter/chapter-3.

[5] S. Solomon et al., eds., Climate Change 2007: The Physical Science Basis (Cambridge (UK): Cambridge University Press, 2007).

[6] Seneviratne et al., “Changes in Climate Extremes and Their Impacts on the Natural Physical Environment.”

[7] J Sillman and E Roeckner, “Indices of Extreme Events in Projections of Anthropogenic Climate Change,” Climatic Change 86, no. 1 (2008): 83–104, doi:10.1007/s10584-007-9308-6; Boberg et al., “Improved Confidence in Climate Change Projections of Precipitation Further Evaluated Using Daily Statistics from ENSEMBLES Models”; Seneviratne et al., “Changes in Climate Extremes and Their Impacts on the Natural Physical Environment.”

[8] IPCC, Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. Special Report of the Intergovernmental Panel on Climate Change, ed. C. B. Field et al. (Cambridge: Cambridge University Press, 2012), fig. 3.10, http://ipcc-wg2.gov/SREX/report/.