A spatially resolved dataset of stable water isotopes in monthly precipitation over Jeju Island, Korea (2000–2003)

Spatially resolved, multi-year observations of stable water isotopes in precipitation remain scarce for high-relief maritime islands. We present a historical dataset of monthly precipitation isotopes collected between September 2000 and December 2003 at 15 stations on Jeju Island, South Korea, spanning elevations of 5–1230 ma.s.l. The dataset contains 462 paired δ ¹⁸ O and δ ² H measurements, deuterium excess ( d -excess =  δ ² H − 8 ×  δ ¹⁸ O), station and sampling metadata, and 488 station-month records of precipitation and air-temperature estimates, including 26 records without corresponding isotope measurements. Missing isotope observations were not imputed. Individual δ ¹⁸ O and δ ² H values range from −13.2 ‰ to −2.0 ‰ and from −93.3 ‰ to −5.8 ‰, respectively, and generally exhibit lower values in summer than during the cool season. Unweighted station means for the common 2002–2003 period yield elevation gradients of −0.146 ± 0.013 ‰ per 100 m for δ ¹⁸ O and −1.043 ± 0.128 ‰ per 100 m for δ ² H, with uncertainties expressed as standard errors. An island–nearshore comparison with isotope-enabled model output provides context for broad seasonal variability. By recovering and openly publishing observations collected more than two decades ago, this dataset preserves a historical baseline for subsequent precipitation-isotope monitoring and hydrological studies on Jeju Island. The data are available at https://doi.org/10.22747/paper_data.20260219.42 (Lee et al., 2026).