Drought is a complex phenomenon and can be defined in many ways. It is globally growing problem that occurs on a time scale from months to years. There are several types of drought. The most known is meteorological drought and the least investigated is groundwater drought. Groundwater drought studies started relatively recently in the last decade. In Slovenia, there are almost no data on groundwater drought.
Groundwater drought can be determined by statistical analysis of groundwater level diagrams in individual observation wells. First method, which was used for analysis, is based on ranking statistics defined by lower deciles indicating low groundwater level. Another approach was based on univariant indices. It is a so-called Standardized Groundwater Index (SGI).
As a case study unconfined Quaternary aquifer of Dravsko-Ptujsko polje was chosen. Accordingly hydrological status of the groundwater deficit for individual observation wells was determined and illustrated on maps and diagrams.
With the analysis of drought periods, on the Dravsko-Ptujsko polje, it turned out that the groundwater deficit between the observation wells appear quite simultaneously, but differ in the intensity and duration of each event. The important conclusion is that the intensity of groundwater drought does not depend on the length of an event. A shorter event can be much more intense than a long lasting event.
Observation wells located on the western rim below Pohorje Mountains have higher amplitude of groundwater fluctuations the others. This has a consequence of more intensive dry periods, with longer duration. On the other hand, the locations in the central and eastern part of the Dravsko polje, have a more damped fluctuation, which leads to less intensive, but more frequent groundwater drought events.