2016 Volume 46 Issue 2 Pages 123-138
To elucidate the spatial distribution and seasonal variability of stable isotopes in precipitation across Japan, the Isotope Mapping Working Group of the Japanese Association of Hydrological Sciences conducted precipitation sampling during an intensive observation period throughout 2013 (IOP2013). More than 2000 precipitation samples were collected at 56 stations, and their stable water isotopes (δ18O, δD) were measured at Kumamoto University. The time-series of δ18O and d-excess of precipitation showed rapid and significant seasonal variability, affected by precipitation type (i.e., the winter monsoon and Nangan-Low) and by the amount of rainfall during the Baiu rainy season. The monthly mean δ18O and d-excess of IOP2013 were averaged in each of six regions across Japan and compared with previous studies, although the sampling periods varied. The seasonal variability of the monthly δ18O anomaly from the annual mean was not coincident, indicating the deviation depended on the sampling period. Conversely, the seasonal variability of the monthly d-excess was coincident, even though the absolute values were averaged. Based on the results of short-term sampling at each station, the temperature effect was found north to 35°N and also the precipitation amount effect was mostly found south to 37°N. Further observational data will be required to increase the spatial resolution for better understanding of the spatiotemporal variability of stable isotopes in precipitation across Japan.
