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| Titel |
Historical droughts in Mediterranean regions during the last 500 years: a data/model approach |
| VerfasserIn |
S. Brewer, S. Alleaume, J. Guiot, A. Nicault |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 3, no. 2 ; Nr. 3, no. 2 (2007-06-22), S.355-366 |
| Datensatznummer |
250000904
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| Publikation (Nr.) |
 copernicus.org/cp-3-355-2007.pdf |
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| Zusammenfassung |
| We present here a new method for comparing the output of General Circulation Models (GCMs)
with proxy-based reconstructions, using time series of reconstructed and simulated climate
parameters. The method uses k-means clustering to allow comparison between different periods
that have similar spatial patterns, and a fuzzy logic-based distance measure in order to take
reconstruction errors into account. The method has been used to test two coupled ocean-atmosphere
GCMs over the Mediterranean region for the last 500 years, using an index of drought stress, the
Palmer Drought Severity Index. The results showed that, whilst no model exactly
simulated the reconstructed changes, all simulations were an improvement over using the mean
climate, and a good match was found after 1650 with a model run that took into account changes in
volcanic forcing, solar irradiance, and greenhouse gases. A more detailed investigation of the
output of this model showed the existence of a set of atmospheric circulation patterns linked to the
patterns of drought stress: 1) a blocking pattern over northern Europe linked to dry conditions in the
south prior to the Little Ice Age (LIA) and during the 20th century; 2) a NAO-positive like pattern
with increased westerlies during the LIA; 3) a NAO-negative like period shown in the model
prior to the LIA, but that occurs most frequently in the data during the LIA. The results of the
comparison show the improvement in simulated climate as various forcings are included and
help to understand the atmospheric changes that are linked to the observed reconstructed climate changes. |
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