Drought variability and trend over the Lombardy plain from meteorological station records

The spatial and temporal variability of droughts over the period 1951–2017 for a portion of Lombardy plain (Northern Italy) was reconstructed starting from a quality-checked and ho-mogenized database of long precipitation and temperature station records covering the study region. The monthly meteorological series were interpolated over the period 1951–2017 onto a 30-arc second resolution grid covering the area by means of an anomaly-based procedure and the gridded fields were used to extract for each cell the series of two standardized drought indices: Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI). SPI and SPEI trend analyses were performed on annual and seasonal scales at both regional and grid-point levels. Theil-Sen test on SPI values highlight-ed a significant drying tendency (Mann-Kendall p-value < 0.05) for summer only (-0.14 dec-ade-1), while SPEI series exhibited a more negative summer trend (-0.22 decade-1) and signif-icant reductions also in spring and annual values (-0.14 and -0.17 decade-1, respectively), suggesting an increase of evapotranspiration rates driven by higher temperature. Moreover, the trend analyses at grid cell level highlighted a greater negative and significant tendency for the western and southern part of the domain. Similar outcomes were obtained by as-sessing the temporal evolution of drought features over the decades in terms of frequency, duration and severity.