High-resolution analysis of daily precipitation trends in the central Alps over the last century

In this work we present a homogenized high-resolution data set composed of 200 daily precipitation series spanning the last 90 years, located over an area centred on the Trentino—South Tyrol region (central part of the European Alps), in a transition zone between the climates of the southern and northern slopes of the Alps. We analysed the trends of total precipitation (TP), wet days (WD) and average intensity (PI), as well as trends of the number of events and precipitation amounts belonging to 12 different daily intensity categories. For an easier understanding of geographical patterns, we set up a gridded data set in terms of anomalies, with a spatial resolution of 0.1°. All the statistics were analysed for trend over the entire period spanned by the data and on subperiods of variable length. On regional average, we found a weak decrease in TP (about 1%/decade with respect to the 1971–2000 mean) over the entire studied period (1922–2009), which was statistically significant only in spring. Gridded data show that the decrease is related to a reduction in the number of WD in the eastern part of the study area, and a decrement in PI in the western part, with orography playing a clear role in this differentiation. On a daily scale, trends of the strongest events present scarce spatial coherence and are only locally significant, however the results are highly dependent on the period analysed. Comparisons with previous low-resolution studies on the same area underline the importance of a high-resolution data set in characterizing spatial variability of climatic trends in precipitation.