Daily precipitation variability in the southern Alps since the late 19th century

We analysed a data set of 18 homogenized daily precipitation series from the southern European Alps, covering approximately the last 150 years. Previously available data from stations in Northern Italy have been extended considerably by recent digitization work, and, for the first time, they have been combined with daily data from Swiss stations on a centennial scale. Precipitation frequency in the southern Alps decreased significantly over the period 1890–2017. We show that this trend is related to a step-like reduction in cyclonic weather types over central Europe that occurred around 1940. This decrease is an example of the large variability that affects precipitation in the region over many different time scales. In particular, strong trends on a decadal scale are related to the Atlantic Multidecadal Oscillation and the North Atlantic Oscillation, although the influence of the latter is present only in the recent decades. Trends in heavy precipitation indices do not show a coherent pattern across the study area. We find a significant increase in heavy precipitation in Switzerland, while a decrease affects the southeastern subset in spring.