Analysis of hydrological cycle in atmosphere using hydrogen and oxygen stable isotope ratios

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We measured oxygen stable isotope ratios (δ ^<18>O) of surface water in Kii Peninsula, and showed their spatial distribution. As a result, the enriched δ ^<18>O composition of surface waters were distributed in the southeast area and the depleted δ ^<18>O composition of surface waters were distributed in the inland area where the altitude was high (>1000 m). In order to understand the spatial distribution of δ ^<18>O composition of surface water, rainfall characteristics were considered as well as topographic effect. We classified the rainfall characteristics with three zones using a ratio of the total number that means how many times precipitation was simultaneously observed between AMeDAS observation stations: 1)the east and southeast area (zone A), 2)the southwest area (zone B), 3)the northwest area (zone C). From the correlation analysis between δ ^<18>O and topographic data, we can find that the zoning effects on the topographic effect, especially in a meso-scale area. Our observation result shows that the δ ^<18>O composition of surface water was enriched in high precipitation area. This result does not correspond to the isotopic amount effect. We think this reasons that continuous vapor supply from the sea keeps δ ^<18>O composition of rain clouds enriched.