Run analysis of potential evapotranspiration and soil moisture  for investigating flash droughts in Sicily

Flash droughts develop and intensify rapidly under the influence of abnormally high temperatures, wind speed, radiation and declining of the normal precipitation rate. The changing of Potential evapotranspiration (PET) and soil moisture is considered as key early warning and development of flash drought indicators.In this study, we first analyse spatio-temporal trends of the PET at monthly, seasonal, and annual temporal scales in Sicily.  PET is estimated by the Penman-Monteith method based on a network of 46 meteorological stations, at daily metrological data. The Mann Kendall test and Sen’s slope analysis are applied to identify the significance of PET trends in the region. Result showed increasing trends for most of the months and the region. For instance, August had the highest increasing PET monthly trend, with a maximum of 1.73 mm per year and the highest increasing annual trend was 10.68 mm per year. Findings of this analysis provide preliminary insights on how climate change can influence PET.Then, we carry out a preliminary investigation of flash droughts based on a joint analysis of potential evapotranspiration and soil moisture. In particular, based both on the network of meteorological stations and reanalysis data  of soil moisture at hourly resolution, daily  potential evapotranspiration (PET) and soil estimations at different soil depths are analysed with the method of runs. Considering different thresholds, the runs of PET and soil moisture are compared to characterize flash drought periods and to understand the relation between the two variables. Results indicate a significant link between the variables, and thus a potential for developing flash drought monitoring tools.  Keywords: Flash drought, Potential evapotranspiration (PET), Spatiotemporal, Trend, Sicily