Long-Term Alpine Precipitation Reconstruction (LAPrec): A Gridded Monthly Data Set Dating Back to 1871

Spatial climate data sets that extend back in time over many decades are an important resource for climate monitoring. The long-term consistency of such data sets is, however, compromised by changes in the measurement systems over time. In this paper, we introduce a data set of monthly precipitation on a 5-km grid over the European Alps that extends back to the late 19th century. In deriving the "long-term Alpine precipitation reconstruction" (LAPrec), special care is taken of variations in the station network, in order for the data set to satisfy high standards in long-term consistency. LAPrec builds on a reconstruction method that integrates the available information in two portions: The first is a set of high-quality homogenized station series, taken from the HISTALP data archive, covering the entire period almost continuously. The second is a high-resolution gridded precipitation analysis, taken from the "Alpine Precipitation Grid Data Set," constructed from thousands of rain-gauges but covering a few decades only. We demonstrate how the reconstruction approach successfully introduces mesoscale structures that are not resolved by the available long-term station series, more plausibly so than a predecessor data set using conventional interpolation. We also illustrate that LAPrec reveals long-term precipitation trends that are spatially more consistent and more detailed than the trends in popular climate monitoring data sets. Over the period 1871-2017 a statistically significant increase is found in winter over the northern parts of the Alps (1%-2% per 10 years). LAPrec is available in two versions (back until 1871 and 1901 respectively) from the Copernicus climate data store. Data sets extending back in time over many decades are an important resource for climate monitoring. In this paper, we introduce a data set on a regular grid of monthly precipitation over the European Alps that extends back to 1871. In deriving the "long-term Alpine precipitation reconstruction" (LAPrec), special care is taken to keep the station network constant and make use of high-quality homogenized time series, in order for the data set to be as consistent as possible over time. LAPrec builds on two sources of information: The first is a set of high-quality station series from the HISTALP data archive, covering the entire period almost continuously. The second is a high-resolution gridded precipitation analysis, the "Alpine Precipitation Grid Data Set," constructed from thousands of rain-gauges but covering a few decades only. We demonstrate how this approach successfully introduces details that are not resolved by the available long-term station series. We also illustrate that LAPrec reveals long-term precipitation trends that are spatially more consistent and detailed than the trends in popular climate monitoring data sets. Over the period 1871-2017 a statistically significant increase in winter precipitation is found over the northern parts of the Alps. LAPrec is available from the Copernicus climate data store. Long-term spatial analyses of precipitation in the European Alps since 1871For applications such as climate monitoring and trend analysis, the data set meets high standards in long-term consistency and homogeneityLong-term Alpine precipitation reconstruction detects a significant trend in winter precipitation over the northern part of the Alps in the period starting from 1871