A water isotope approach to assessing moisture recycling in the island-based precipitation of Taiwan:A case study in the western Pacific

摘要

This study employs a dual-isotope (δ~(18)O and δD), three-end-member linear mixing model to semiquantitatively assess vapor contributions of advection, transpiration, and evaporation to precipitation, and to compare the extent of moisture recycling (including transpiration and evaporation) among areas of various topographic types in Taiwan, an island located in the western Pacific. The three topographic types examined are the mountainous regions, foothill regions (as represented by two reservoir stations), and coastal plains. Results indicate that the moisture fractions from advection and evapotranspiration in mountain precipitations are about 63% and 37%, respectively, and those in precipitation of plain and foothill regions are about 69% and 31%, respectively. Moreover, transpiration accounts for most of the recycling moisture while evaporation offers minor contribution. Since the transpiration fraction of recycling moisture is higher in forest mountain area than in plain/foothill region, topographic type is the major factor affecting the extent of transpiration. Nevertheless, the two reservoirs examined in this study do not offer significant contribution of recycling moisture to local precipitation. In addition to topographic type, temperature and rainfall may be two other factors controlling the extent of transpiration; transpiration would be promoted in greater rainfall regions but reduced in higher temperature areas. Additionally, about 25% of precipitation in plain/foothill region is of relocated moisture from evapotranspiration induced from forest mountains. It should be noted that this isotope-based approach has its limitations and should be applied with caution.