Isotopic Composition of Precipitation in Small Pannonian Catchments

The Pannonian Basin in Central Europe is facing growing challenges regarding water security and pressures stemming from frequent droughts and floods, intensive agriculture, and the depletion of non-renewable groundwater reserves. To support catchment-scale water resource research, this study presents precipitation isotopic data from two small Pannonian catchments: the Ledava (Slovenia) and the Koppány catchment (Hungary). The dataset comprises monthly meteorological data (precipitation (P), air temperature (T)) together with isotopic data (stable isotopes of hydrogen (δ2H) and oxygen (δ18O), deuterium excess (d-excess), and tritium activity concentration (A)) from Murska Sobota–Rakičan (2015–2024) alongside two shorter isotope records from stations Törökkoppány and Tamási (2022–2024). Data reveal a pronounced annual cycle, reflecting the influence of seasonal temperature on isotopic composition. Tritium concentrations display an opposite seasonal pattern to d-excess with enhanced atmospheric mixing and stratosphere–troposphere exchange during the warm season. Local Meteoric Water Lines (LMWLs) computed for both catchments distinguish a wetter, western isotope-hydroclimatic domain from a drier, more continental one, consistent with a transitional zone across southwestern Transdanubia. Together, these datasets and LMWLs establish a decadal isotopic baseline for climatological and hydrological studies, including groundwater recharge assessment, across the Pannonian Basin.