CLIVALP - Climate Variability Studies in the Alpine Region

Long term meteorological observations carried out in the Alps and their surroundings offer a large research potential for climate change studies which has not been utilised in its full capacity yet. During the last decade a number of national and international attempts in the Alpine countries have significantly increased data quality in terms of long-term homogeneity. Therefore the feasibility is given now for the following project aims: to describe climate variability as a whole as an inter-connected system of multiple climate datasets. This will be done on the basis of homogenised long-term instrumental series of a number of climate elements with a time resolution of one month. to analyse special periods with prominent deviations from the long-term average climate in time slices of five to twenty years in a more detailed way, e.g. the 1980ies and 1990ies (too warm), the temperature maximum around 1950, the maritime phase of the 1910s, the continental phase of the 1890ies, the dry period around 1860, the volcano driven cool summers 1813 to 1817, the second main warm period near 1800. to elaborate new circulation indices relevant for the Alps based on homogenised long-term air pressure series from the Alps and four remote regions in the North, the South, the East and the West. to analyse regional differences, spatial representativity, inter-dependencies and circulation driven forcings of the long-term climate elements. to compare Alpine gridpoint-series of high spatial density with existing global datasets (NOAA-NCDC, UEA- CRU). All studies within the proposed project will be based on carefully homogenised long term climate time series of the instrumental period which covers one and a half to two and a half centuries in the study area. The study area covers the Alps and their surroundings (approximately 4 to 18 deg E, 43 to 49 deg N).

The Alpine region offers a unique potential of historical climate data regarding temporal lengths, spatial resolution, and vertical extension. This potential has not been exploited yet, hence CLIVALP - CLimate Variability studies in the ALPine region - took the initiative to make use of it guided by the watchword: "Learning from the Past for the Future". The HISTALP database (Historical Instrumental Climatological Surface Time series for the Alpine region), which has been developed and systematically implied within CLIVALP, has already formed an ideal basis for investigations of climate and its variability and it will certainly continue to satisfy this concern in the future. It is a homogenized, multi-elemental database (72 series of air pressure, 131 of temperature, 192 of precipitation, 55 and 66 of sunshine and cloudiness, respectively) reaching back into the early instrumental period and allowing for a large range of studies concerning Alpine climate. The longest temperature and air pressure series extend back to 1760, precipitation to 1800, cloudiness into the 1840s and sunshine into the 1880s. CLIVALP assessed potential future changes of climate impact parameters via non linear relationships with temperature. Such sensitivity studies were highlighted considering frost frequency as example. A future temperature increase, for instance, of 1 K translates into a decrease of frost days per year, which can be, depending on location and season, as high as 15 days. During winter, for example, low elevated regions from Innviertel along the Danube valley to the Weinviertel and southwards to the Grazer Becken exhibit highest sensitivity values of over six days of frost reduction. In summer the affected regions are along the Alpine chain raising the matter of permafrost etc. More than two centuries of high quality climate data also allowed for the detection of multi-annual to decadal periods showing significant anomalies for a large fraction of records. Such periods, called `outstanding` have an impact on society, agriculture and leave their marks in the scenery as e.g. glacier advances or retreats. Actually, HISTALP data were used to explain glacial changes by the variability of air temperature, precipitation, sunshine, and cloudiness. CLIVALP also contributed to understanding the effect of external forcings on European/Alpine scale climate. This was achieved by combining HISTALP and ensemble simulations, carried out with a coupled General Circulation Model, driven by different external forcings. These high standard and expensive simulations were provided by the GKSS Research Centre, Geesthacht. Based on outstanding periods we analyzed atmospheric circulation of those simulations that satisfyingly reproduced surface temperature conditions. Thereby it was possible to address different circulation modes to different warm and cool phases of outstanding periods. Results are regarded as promising and in agreement with the physical understanding of atmospheric circulation. Due to the larger sample size findings for winter and the year as a whole are found to be as more reliable than those for summer.