A validation of ADO drought indices SPI and SPEI in Slovenia

Drought indices are essential for tracking and warning of the possible drought related effects, impacts and outcomes (WMO and GWP, 2016). The use of a specific drought index in this manner requires a prior assessment of the index performance in detecting and monitoring different types of drought. Agricultural drought affects plants and crops, sometimes resulting in extensive crop failure. As agricultural drought is particularly relevant for the Alpine region and the Slovenian case study area, we investigated the ability of SPI and SPEI to detect agricultural drought through validation against annual yield data for several crops and types of grassland, averaged to statistical regions (NUTS3 level). Prior to evaluating indices against yield data, we evaluated SPI and SPEI values calculated from ERA5 reanalyses against SPI and SPEI values calculated from ground observations at representative meteorological stations in Slovenia in order to learn whether the indices calculated in the Alpine domain are relevant on a national level.