EEAR-Clim: a high-density observational dataset of daily precipitation and air temperature for the Extended European Alpine Region

The Extended European Alpine Region (EEAR) exhibits a well-established and very high density network of in situ weather stations, hardly attained in other mountainous regions of the world. However, the strong fragmentation of the area into national and regional administrations and the diversity of data sources have hampered the full exploitation of the available data for climate research. Here, we present EEAR-Clim, a new observational dataset gathering in situ daily measurements of air temperature and precipitation from a variety of meteorological and hydrological services covering the whole EEAR. The data collected include time series from recordings of diverse lengths up to 2020, with the longest records spanning up to 200 years. The overall observational network encompasses about 9000 in situ weather stations, significantly enhancing data coverage at high elevations compared to existing datasets and achieving an average spatial density of one station per 6.8 km2 over the 1991–2020 period, the most covered by measurements. Data collected from many sources were tested for quality to ensure the internal, temporal, and spatial consistency of time series, including outlier removal. Data homogeneity was assessed through a cross-comparison of the break points detected by three methods that are well established in the literature, namely Climatol, ACMANT, and the RH test. Quantile matching was applied to adjust inhomogeneous periods in time series. Overall, about 4 % of data were flagged as unreliable, and about 20 % of air temperature time series were corrected for one or more inhomogeneous periods. In the case of precipitation time series, fewer break points were detected, confirming the well-known challenge of properly identifying inhomogeneities in noisy data. The high quality, homogeneity, unprecedented spatial density, and completeness of data and the inclusion of the most recent records are important add-on improvements compared to other observational products available for the EEAR. The dataset (https://doi.org/10.5281/zenodo.10951609, Bongiovanni et al., 2024) aims to serve as a powerful tool to better understand climate change and climatic variability over the European Alps.