A regional scale data–model comparison of modern oxygen stable isotopes in precipitation (Swabian Alb, southwest Germany)

The analysis of isotopic composition (δ¹⁸O and δ²H) in precipitation is a powerful approach for investigating (paleo)climatic processes within the hydrological cycle. Variations in δ¹⁸O and δ²H in precipitation result from successive isotopic fractionation processes during atmospheric transport and are observed across both spatial and temporal scales. While modern isotopic records are extensively documented, e.g., through the IAEA/WMO network, European datasets are largely limited to monthly resolution and remain sparse at the regional scale. This is particularly the case for the Swabian Alb (or Swabian Jura) in southwestern Germany, a karst plateau south of Stuttgart, approximately 220 km long and 40 km wide, with mean elevations around 500 m and peaks reaching 1110 m. The Swabian Alb holds international significance as a UNESCO Global Geopark and includes six caves designated as UNESCO World Heritage sites. The region constitutes a natural divide between two significant European basins: the Rhine and the Danube. The oxygen isotopic composition of meteoric water from the Swabian Alb provides key insights into modern moisture sources and, when preserved in paleoclimate archives such as speleothems, offers valuable information on past atmospheric circulation and hydroclimate.

Here, we compare measured δ¹⁸O and δ²H in meteoric water with simulations of isotope-enabled climate model (ECHAM6-wiso) to investigate spatial and temporal variabilities, and identify climatic factors influencing regional isotopic patterns. We present δ¹⁸O and δ²H records of weekly to monthly sampled rainwater across the Swabian Alb from October 2023 to present-day. We examine simulated and observed interannual changes in precipitation, teleconnections, and seasonality patterns. In addition, we fill a gap by providing daily δ¹⁸O and δ²H values of meteoric water collected at a weather station located in Tübingen.

Investigating variations in modern water isotope records across the Swabian Alb is essential for regional paleoclimate research and allows the validation of isotope-enabled climate models on the local scale. Our results show the first model–data comparison for the Swabian Alb and pave the way towards regional climatic reconstructions e.g., paleoclimate of the last glacial period, when modern humans occupied caves of the Swabian Alb.