RAINFALL-TOPOGRAPHY EFFECT ON SPATIAL DISTRIBUTION OF STABLE ISOTOPE RATIOS OF SURFACE WATER IN KII PENINSULA

Abstract

We measured oxygen stable isotope ratios (δ¹⁸O) of surface water in Kii Peninsula, and showed their spatial distribution. As a result, the enriched δ¹⁸O composition of surface waters were distributed in the southeast area and the depleted δ¹⁸O 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 δ¹⁸O 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 δ¹⁸O and topographic data, we can find that the zoning effects on the topographic effect, especially ina meso-scale area. Our observation result shows that the δ¹⁸O composition of surface water was enriched in highprecipitation area. This result does not correspond to the isotopic amount effect. We think this reasons that continuous vapor supply from the sea keeps δ¹⁸O composition of rain clouds enriched.