How reliable are modeled precipitation isoscapes over a high-relief mountainous region?

Precipitation isotope maps over mountains are critical for water resource assessment, yet isoscape modeling has been minimally investigated for complex terrain with high relief. Here we show that multiannual (2011–2015) mean precipitation isoscapes across the Japanese Alps region can be represented by simple multiple-regression models with strong goodness of fit (R2 = 0.928 for δ2H and 0.944 for δ18O). Reliability of the models was further confirmed by agreement with previously reported independent data throughout a wider range of elevation (7–3,730 m asl). Modeled precipitation isoscapes were consistent with observations of soil water (20 sites) and river water (50 sites) when considering evaporative enrichment and unclosed water balance. Uncertainties of modeled δ values for precipitation were greater in lowlands near the coast than over the mountains. Unexpectedly, spatially uniform isotopic lapse rates (–11.66‰ km–1 for δ2H and –1.724‰ km–1 for δ18O), which are divorced from continental effects, gave substantially good approximation on a regional (e.g., a few hundred kilometers) scale. This allows for convenient and reliable modeling of precipitation isoscapes over mountainous regions for hydrological/ecological/interdisciplinary applications.