Increase in intense precipitation in the Alps over the last century

Precipitation trends in the Alps have been studied by a team of researchers [[from the Institute of Environmental Geosciences (IGE/OSUG, CNRS / IRD / UGA / Grenoble INP), the National Center for Meteorological Research (CNRM, CNRS / Météo-France) and the University of Liege (Belgium)], by comparing the outputs of the regional atmospheric model MAR with local meteorological observations over the period 1903-2010.}.

The increase in precipitation with altitude has been estimated, on average over the Alps, at 38% km-1 in winter and 33% km-1 in summer, with, however, strong spatial disparities. A marked decrease in precipitation was found in the plains south of the Alps, reaching -20 to -50% over the period 1903-2010, a drying up due to a decrease in the number of rainy days in spring and summer. In the mountains in the north-western part of the Alps, an increase of 20 to 40% in winter precipitation was recorded over the period 1903-2010. This positive trend is modulated by strong decadal variability, which has generated a negative trend since the 1960s. The average annual maximum daily precipitation over the period 1903-2010 varies between 30 and 100 mm per day over the Alpine arc. This index, often used for the study of extreme rainfall, has intensified by 20 to 40% over the period 1903-2010 in most parts of the Alps. These results show that series with a minimum duration of 50 to 80 years are necessary to calculate trends emerging from the high interannual variability of this index. In addition, an acceleration of the increase in intense precipitation over the last decades is observed.

MAR simulation (background map) and local observations (MeteoSwiss data) of the average annual maximum rainfall over the period 1971-2008 (a) and its trend over the period 1903-2010 (b). Contour lines (500 m apart) are shown as thin black lines and national boundaries as bold dashed lines.

This work confirms that the study of climate and the identification of climatic events likely to have strong socio-environmental impacts require meteorological data covering long periods.

This study is part of TRAJECTORIES, a project aimed at studying socio-environmental trajectories in the Alps.

Local Scientific Contact

Martin Menegoz->http://pp.ige-grenoble.fr/pageperso/menegozm/], IGE / OSUG

Article initially published by the INSU CNRS.