[A-HW22] Hydrological Cycle and Water Environment

[AHW22-15] Factors controlling seasonal variation of stable isotopes in precipitation across Japan

*Takayki Uesugi¹, Kimpei Ichiyanagi¹, Masahiro Tanoue², Kei Yoshimura² (1.Kumamoto University, 2.Then University of Tokyo)

Keywords:stable isotopes in precipitation, the Baiu rainy season, precipitation amount effect

This study tried to estimate factors controlling stable isotopes in precipitation across Japan by using observation and model simulation. Observation of stable isotopes in precipitation were conducted by the Isotope Mapping Working Group of Japanese Association of Hydrological Sciences (IMWG/JAHS) throughout 2013. Also, stable isotopes in precipitation and water vapor were simulated by using a regional spectral model incorporated water isotopes (IsoRSM) with a horizontal resolution of 30km. In order to validate the simulation results, simulated monthly anomaly of δ¹⁸O from the annual mean values at 78 stations were averaged depend on the 7 climate regions and compared with observation. The correlation coefficients of them were over 0.70 with statistically significance.

Spatial distributions of observed δ¹⁸O in precipitation across Japan show clear latitude effect in spring, fall and winter seasons, but that did not show in summer season. And, observed monthly δ¹⁸O in precipitation of June were lower than those for adjacent months in 6 climate regions except Northern Japan region. As a result of the IsoRSM simulation, spatial distribution of monthly δ¹⁸O in water vapor across Japan from June to September ranged from -22 to -20 permil and did not show the latitude effect. In the Baiu rainy season of 2013, precipitation amount was high in regions south of the Northern Japan region. It is suggested that monthly δ¹⁸O in precipitation was depleted by the amount effect in these regions. On the other hand, monthly δ¹⁸O in precipitation from June to September show the temperature effect in the Northern Japan region.