Potential future changes in the characteristics of daily precipitation in Europe simulated by the HIRHAM regional climate model |
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| Authors: | Wilhelm May |
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| Institution: | (1) Danish Climate Centre, Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark |
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| Abstract: | In this study the potential future changes in various aspects of daily precipitation events over Europe as a consequence of
the anticipated future increase in the atmospheric greenhouse gas concentrations are investigated. This is done by comparing
two 3-member ensembles of simulations with the HIRHAM regional climate model for the period 1961–1990 and 2071–2100, respectively.
Daily precipitation events are characterized by their frequency and intensity, and heavy precipitation events are described
via 30-year return levels of daily precipitation. Further, extended periods with and without rainfall (wet and dry spells)
are studied, considering their frequency and length as well as the average and extreme amounts of precipitation accumulated
during wet spells, the latter again described via 30-year return levels. The simulations show marked changes in the characteristics
of daily precipitation in Europe due to the anticipated greenhouse warming. In winter, for instance, the frequency of wet
days is enhanced over most of the European continent except for the region on the Norwegian west coast and the Mediterranean
region. The changes in the intensity and the 30-year return level of daily precipitation are characterized by a similar pattern
except for central Europe with a tendency of decreased 30-year return levels and increased precipitation intensity. In summer,
on the other hand, the frequency of wet days is decreased over most of Europe except for northern Scandinavia and the Baltic
Sea region. In contrast, the precipitation intensity and the 30-year return level of daily precipitation are increased over
entire Scandinavia, central and eastern Europe. The changes in the 30-year return level of daily precipitation are generally
stronger than the corresponding changes in the precipitation intensity but can have opposite signs in some regions. Also the
distribution of wet days is changed in the future. During summer, for instance, both the frequency and the length of dry spells
are substantially increased over most of the European continent except for the Iberian Peninsula. The frequency and the length
of wet spells, on the other hand, are generally reduced during summer and increased during winter, again, with the exception
of the Iberian Peninsula. The future changes in the frequency of wet days in winter are related to a change in the large-scale
flow over the North Atlantic and a corresponding shift of the North Atlantic storm track. The reduction in the frequency of
wet days in summer is related to a northward extension of the dry subtropical region in the future, with a reduction of the
convective activity because of the large-scale sinking motion in the downward branch of the Hadley cell. Because the atmosphere
contains more moisture in the warmer future climate, the amount of precipitation associated with individual low-pressure systems
or with individual convective events is increased, leading to a general increase in the intensity of individual precipitation
events. Only in regions, where all the moisture evaporates from the ground already in spring, the intensity of precipitation
events is reduced in summer. |
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