GROUNDWATER TEMPERATURE IN SLOVENIA SINCE 2015

Abstract

The groundwater temperature in the intergranular aquifers of Slovenia generally ranges between 8 and 15°C and has been increasing over time, both annually and seasonally. The lowest groundwater temperatures are characteristic of the Kranjsko and Sorško polje aquifers, as well as the Tržiška Bistrica aquifer, while the highest are found in the Čateško, Vrtojbensko, and Ljubljansko polje aquifers. The monthly average groundwater temperatures from the 2015–2023 observation period show different degrees of variability in the aquifers. Higher variability is typical of shallower aquifers exposed to seasonal air temperature changes, while lower variability is found in deeper aquifers. Seasonal fluctuations in groundwater temperature are smoothed and delayed compared to air temperatures, with the amplitude of variation decreasing with depth. We identified distinct regimes of groundwater temperature fluctuation. One regime includes monitoring sites in deeper aquifers of the Ljubljana Basin, Vrtojbensko, Dravsko, and Krško polje. Another regime comprises shallower aquifers across the country. A separate thermal regime is observed at sites hydraulically connected to surface waters.