Contrasting seasonal changes in total and intense precipitation in the European Alps from 1903 to 2010
<p>Changes in precipitation over the European Alps are investigated with the regional climate model MAR (Modèle Atmosphérique Régional) applied with a 7 km resolution over the period 1903–2010 using the reanalysis ERA-20C as forcing. A comparison with several observational datasets...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://hess.copernicus.org/articles/24/5355/2020/hess-24-5355-2020.pdf |
| Summary: | <p>Changes in precipitation over the European Alps are investigated with the
regional climate model MAR (Modèle Atmosphérique Régional) applied with a 7 km resolution over the period 1903–2010 using the reanalysis ERA-20C as forcing. A comparison with several observational datasets demonstrates that the model is able to reproduce the climatology as well as both the interannual variability and the seasonal cycle of precipitation over the European Alps. The relatively high resolution allows us to estimate precipitation at high elevations. The vertical gradient of precipitation simulated by MAR over the European Alps reaches 33% km<span class="inline-formula"><sup>−1</sup></span> (1.21 mm d<span class="inline-formula"><sup>−1</sup></span> km<span class="inline-formula"><sup>−1</sup></span>) in summer and 38 % km<span class="inline-formula"><sup>−1</sup></span> (1.15 mm d<span class="inline-formula"><sup>−1</sup></span> km<span class="inline-formula"><sup>−1</sup></span>) in winter, on average, over 1971–2008 and shows a large spatial variability. A significant (<span class="inline-formula"><i>p</i></span> value <span class="inline-formula"><</span> 0.05) increase in mean winter precipitation is simulated in the northwestern Alps over 1903–2010, with changes typically reaching 20 % to 40 % per century.
This increase is mainly explained by a stronger simple daily intensity index (SDII) and is associated with less-frequent but longer wet spells. A general drying is found in summer over the same period, exceeding 20 % to 30 % per century in the western plains and 40 % to 50 % per century in the southern plains surrounding the Alps but remaining much smaller (<span class="inline-formula"><10</span> %) and not significant above 1500 m a.s.l. Below this level, the summer drying is explained by a reduction in the number of wet days, reaching 20 % per century over the northwestern part of the Alps and 30 % to 50 % per century in the southern part of the Alps. It is associated with shorter but more-frequent wet spells. The centennial trends are modulated over the last decades, with the drying occurring in the plains in winter also affecting high-altitude areas during this season and with a positive trend of autumn precipitation occurring only over the last decades all over the Alps. Maximum daily precipitation index (Rx1day) takes its highest values in autumn in both the western and the eastern parts of the southern Alps, locally reaching 50 to 70 mm d<span class="inline-formula"><sup>−1</sup></span> on average over 1903–2010. Centennial maxima up to 250 to 300 mm d<span class="inline-formula"><sup>−1</sup></span> are simulated in the southern Alps, in France and Italy, as well as in the Ticino valley in
Switzerland. Over 1903–2010, seasonal Rx1day shows a general and significant increase at the annual timescale and also during the four seasons, reaching local values between 20 % and 40 % per century over large parts of the Alps and the Apennines. Trends of Rx1day are significant (<span class="inline-formula"><i>p</i></span> value <span class="inline-formula"><</span> 0.05) only when considering long time series, typically 50 to 80 years depending on the area considered. Some of these trends are nonetheless significant when computed over 1970–2010, suggesting a recent acceleration of the increase in extreme precipitation, whereas earlier periods with strong precipitation also occurred, in particular during the 1950s and 1960s.</p> |
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| ISSN: | 1027-5606 1607-7938 |