Abstract:This paper describes the HISTALP database, consisting of monthly homogenised records of temperature, pressure, precipitation, sunshine and cloudiness for the 'Greater Alpine Region' (GAR,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(43)(44)(45)(46)(47)(48)(49). The longest temperature and air pressure series extend back to 1760, precipitation to 1800, cloudiness to the 1840s and sunshine to the 1880s. A systematic QC procedure has been applied to the series and a high number of inhomogeneities (more than 2500) and outliers (more than 5000) have been detected and removed. The 557 HISTALP series are kept in different data modes: original and homogenised, gap-filled and outlier corrected station mode series, grid-1 series (anomaly fields at 1°× 1°, lat × long) and Coarse Resolution Subregional (CRS) mean series according to an EOF-based regionalisation. The leading climate variability features within the GAR are discussed through selected examples and a concluding linear trend analysis for 100, 50 and 25-year subperiods for the four horizontal and two altitudinal CRSs. Among the key findings of the trend analysis is the parallel centennial decrease/increase of both temperature and air pressure in the 19th/20th century. The 20th century increase (+1.2°C/+1.1 hPa for annual GAR-means) evolved stepwise with a first peak near 1950 and the second increase (1.3°C/0.6hPa per 25 years) starting in the 1970s. Centennial and decadal scale temperature trends were identical for all subregions. Air pressure, sunshine and cloudiness show significant differences between low versus high elevations. A long-term increase of the high-elevation series relative to the low-elevation series is given for sunshine and air pressure. Of special interest is the exceptional high correlation near 0.9 between the series on mean temperature and air pressure difference (high-minus low-elevation). This, further developed via some atmospheric statics and thermodynamics, allows the creation of 'barometric temperature series' without use of the measures of temperature. They support the measured temperature trends in the region. Precipitation shows the most significant regional and seasonal differences with, e.g., remarkable opposite 20th century evolution for NW (9% increase) versus SE (9% decrease). Other long-and short-term features are discussed and indicate the promising potential of the new database for further analyses and applications.

The paper describes the development of a dataset of 192 monthly precipitation series covering the greater alpine region (GAR,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). A few of the time series extend back to 1800. A description is provided of the sometimes laborious processes that were involved in this work: from locating the original sources of the data to homogenizing the records and eliminating as many of the outliers as possible. Locating the records required exhaustive searches of archives currently held in yearbooks and other sources of the states, countries and smaller regional authorities that existed at various times during the last 200 years. Homogeneity of each record was assessed by comparison with neighbouring series, although this becomes difficult when the density of stations reduces in the earliest years. An additional 47 series were used, but the density of the sites in Austria and Switzerland was reduced to maintain an even coverage in space across the whole of the GAR. We are confident of the series back to 1840, but the quality of data before this date must be considered poorer. Of all of the issues involved in homogenizing these data, perhaps the most serious problem is associated with the differences in the height above ground of the precipitation gauges, in particular the general lowering of gauge heights in the late 19th century for all countries, with the exception of Italy. The standard gauge height in the early-to-mid 19th century was 15-30 m above the ground, with gauges being generally sited on rooftops. Adjustments to some series of the order of 30-50% are necessary for compatibility with the near-ground location of gauges during much of the 20th century. Adjustments are sometimes larger in the winter, when catching snowfall presents serious problems. Data from mountain-top observatories have not been included in this compilation (because of the problem of measuring snowfall), so the highest gauge sites are at elevations of 1600-1900 m in high alpine valley locations. Two subsequent papers will analyse the dataset. The first will compare the series with other large-scale precipitation datasets for this region, and the second will describe the major modes of temporal variability of precipitation totals in different seasons and determine coherent regions of spatial variability.

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[1] Temperate deep freshwater lakes are important resources of drinking water and fishing, and regional key recreation areas. Their deep water often hosts highly specialised fauna surviving since glacial times. Theoretical and observational studies suggest a vulnerability of these hydro-ecosystems to reduced mixing and ventilation within the ongoing climatic change. Here we use a numerical thermal lake model, verified over the 20th century, to quantify the transient thermal behaviour of two European lakes in response to the observed 20th-century and predicted 21th-century climate changes. In contrast to Lac d'Annecy (France) which, after adaptation, maintains its modern mixing behaviour, Ammersee (Germany) is expected to undergo a dramatic and persistent lack of mixing starting from $2020, when European air temperatures should be $1°C warmer. The resulting lack of oxygenation will irreversibly destroy the deepwater fauna prevailing since 15 kyrs. [2] The impacts of future climate change on freshwater systems have been investigated using three approaches: (i) synoptic-scale vulnerability assessments based on modern climate/biodiversity relationships [Magnuson et al., 1997;Moore et al., 1997;Stenseth et al., 2002]; (ii) lake-specific observations showing recent changes in ice-cover duration [Magnuson et al., 2000], instrumental lake vertical temperature profiles, mixing behaviour, and eventually ecological consequences Verburg et al., 2003;Quayle et al., 2002;Carvalho and Kirika, 2003;Dabrowski et al., 2004;King et al., 1999;Livingstone, 2003]; (iii) lake-specific steady-state numerical modelling for idealized climatic changes [Blenckner et al., 2002;Peeters et al., 2002]. However, in order to face future potential impact as expected from these studies, regional administrations require quantitative and temporal forecasting for each lake, which can only be provided by dynamical lake-specific modelling .[3] Here we explore the transient thermal behaviour of two European lakes to recent and future climatic changes. Lac d'Annecy (France), and Ammersee (Germany) are both deep pre-alpine lakes, well documented by instrumental meteorological and lake observations. The benthic faunal assemblage preserved in the deep lake sediments indicates that the bottom waters have been regularly ventilated throughout at least the last 15 000 years [von Grafenstein et al., 1999]. These specific lakes were chosen originally because they are representative of the two main types of mid-latitude deep lakes. In deep and fresh lakes, the springsummer surface heating induces the formation of a warm and light water layer (epilimnion), which ''floats'' over the colder and denser hypolimnion. The winter turn-over occurs when the density of the epilimnion is close enough to the density of the hypolimnion to allow wind-driven full mixing and oxygenation of the bottom water [Famer and Carmack, 1982]. Due to the large seasonal cycle of local temperatures and the high water-discharge rates, we consider only the thermodynamic control of temperature on...