Spatio-temporal variability and trends of drought indices over lombardy plain (Northern Italy) from meteorological station records (1951–2017)

A 30-arc second resolution gridded dataset of 1951–2017 monthly series of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) for a portion of Po Plain in Lombardy region (northern Italy) is presented. The series were derived from an archive of homogenized and quality-checked meteorological station observations covering the study area and its surroundings, which were interpolated onto regular grid by means of an anomaly-based procedure. A significant negative trend in mean regional SPI series was depicted for summer (-0.14 decade-1) while stronger decreases were found for SPEI in spring, summer and year (-0.14,-0.22 and-0.17 decade-1, respectively). The greatest drying tendencies occur in the southern and western parts of domain where summer index trends reached-0.23 and-0.30 decade-1, respectively. The more negative trends of SPEI than SPI can be probably explained by the increasing role of evapotranspiration over recent decades triggered by arising temperature. The assessment of spatio-temporal variability of drought features (frequency, duration and severity) pointed out increasing tendencies in all cases, especially in the western portion of the region.