Evaporative effects on day-to-day precipitation isotope variability in East Asia

Abstract Isotopes in precipitation are valuable for tracking water cycles and material transport. Given increasing demand for dynamic models that simulate isotopic variations on daily or shorter timescales, this study aims to enhance an isoscape model with day-to-day variability by incorporating detailed evaporative isotopic processes. Here, we conduct hourly simulations using four reanalysis datasets (JRA-3Q, JRA-55, ERA5, and MERRA-2) for the period from 1996 to 2003. The daily- and event-based outputs are validated using observed isotopic data from maritime (Kanto Plain), intermediate (North China Plain), and continental (Mongolian Plateau) climate regions. The simulations generally captured the observed variations, with the highest accuracy in the Kanto Plain (root-mean-square error = 1.61‰ for δ 18 O). However, the accuracy is relatively low in the other two areas due to strong influences of uncertainties in soil and groundwater isotopes on precipitation isoscapes. The reproducibility of the d-excess is lower than that of the δ values, with raindrop evaporation having a heavy influence. These findings demonstrate that interdiurnal isotopic variation in precipitation is strongly influenced by both atmospheric water vapor transport/condensation and evaporation from the Earth’s surface and raindrops. Thus, better parameterizations of isotopic fractionation during evaporation would improve the reproducibility of precipitation isoscapes with day-to-day variability.