A spatially resolved 39-month dataset of precipitation water isotopes over Jeju volcanic island, Korea

Abstract. Spatially and temporally resolved observations of precipitation water isotopes are essential for quantifying groundwater recharge, constraining hydroclimate variability, and calibrating paleoclimate proxies, yet such datasets remain scarce for monsoon-influenced volcanic islands characterized by steep topography and strong maritime and continental interactions. Here, we present a spatially resolved 39-month dataset (September 2000 to December 2003) of precipitation water isotopes (δ¹⁸O, δD, and d-excess) collected from 15 monitoring stations across Jeju volcanic island, South Korea, spanning elevations from 10 to 1,500 m above sea level. The dataset comprises 462 precipitation samples and captures pronounced seasonal variability together with island-wide spatial gradients. Monthly mean isotope values exhibit a distinct monsoon-driven seasonal cycle, with isotopic depletion during summer and enrichment during winter, which is well represented by sinusoidal fitting for δ¹⁸O and δD. Spatial analyses reveal a clear altitude effect, with mean lapse rates of −0.15 ‰ per 100 m for δ¹⁸O and −1.1 ‰ per 100 m for δD, while d-excess displays weaker elevation dependence but pronounced seasonal sensitivity to moisture source humidity and evaporation conditions. This dataset provides a robust observational basis for developing high-resolution regional isoscapes, estimating groundwater recharge elevations, and serving as benchmark input and validation data for isotope-enabled climate and hydrological models. All data are openly available with comprehensive metadata, enabling direct reuse in hydrological, climatological, and paleoclimate studies across monsoon-affected volcanic island environments.