Assessment of parallel precipitation measurements networks in Piedmont, Italy

Long historical climate records usually contain non-climatic changes that can influence the observed behaviour of meteorological variables. The availability of parallel measurements offers an ideal occasion to study these discontinuities as they record the same climate. The transition from manual to automatic measurements has been analysed in this study. The dataset has been obtained from two independent climate networks in the Piedmont region, in Northwest Italy. From this dataset, 17 pairs of stations with up to 17 years of overlapping have been identified. On average the overlapping period is 12 years with 8760 daily data matched for a pair of stations. This dataset has proven valuable because it has made it possible to study a set of independently managed pairs of standard-quality stations, while most previous studies in this field analysed data from well-maintained instruments with the same operator, often at meteorological offices. The transition between two networks has highlighted important differences in the amount of precipitation and in the number of rainy days. On average, the automatic network has measured 12% less precipitation and has recorded 9% more rainy days (8 days) per year than the manual network. Both of these differences produce a spurious change in the precipitation of the analysed area, thus showing the importance of having a homogeneous dataset to identify real climate variations.