Regional-scale analysis of extreme precipitation from short and fragmented records

Rain gauge is the oldest and most accurate instrument for rainfall measurement, able to provide long series ofreliable data. However, rain gauge records are often plagued by gaps, spatio-temporal discontinuities and in-homogeneities that could affect their suitability for a statistical assessment of the characteristics of extremerainfall. Furthermore, the need to discard the shorter series for obtaining robust estimates leads to ignore asignificant amount of information which can be essential, especially when large return periods estimates aresought. This work describes a robust statistical framework for dealing with uneven and fragmented rainfallrecords on a regional spatial domain. The proposed technique, named“patched kriging”allows one to exploit allthe information available from the recorded series, independently of their length, to provide extreme rainfallestimates in ungauged areas. The methodology involves the sequential application of the ordinary krigingequations, producing a homogeneous dataset of synthetic series with uniform lengths. In this way, the errorsinherent to any regional statistical estimation can be easily represented in the spatial domain and, possibly,corrected. Furthermore, the homogeneity of the obtained series, provides robustness toward local artefactsduring the parameter-estimation phase. The application to a case study in the north-western Italy demonstratesthe potential of the methodology and provides a significant base for discussing its advantages over previoustechniques.