The isotope data set incorporates individual tree growth and triple isotope (carbon, oxygen and hydrogen) data from eight Fagus sylvatica L. (beech) trees located in Hardwald (Basel, Switzerland) where beech exhibited drought-induced premature leaf discoloration and shedding in summer 2018 (early browning). The trees were selected for tree increment coring from the dataset published in Frei et al. (2022) and Wohlgemuth et al. (2020). The tree-ring data was analyzed and published in Neycken et al. (in preparation). More detailed information about the tree selection and sample preparation can be found in the respective publications.