Stable isotope ratios of typhoon rains in Fuzhou, Southeast China, during 2013-2017

摘要

Stable isotope ratios (delta H-2 and delta O-18) in precipitation not only show a certain response to climate change at different time scales, but also have strong linkages to extreme weather events such as tropical cyclones (hurricanes/typhoons). Typhoon activity in the coastal region of Southeast China is quite intense, bringing huge amounts of moisture; thus, contributing to extreme rainfall in this region. The existing isotope data in Southeast China is available on a monthly or daily temporal resolution, which is inadequate to study 1-2-day-long typhoon rainfall events at a particular location. In this study, hourly rainfall delta H-2 and delta O-18 data are collected for eight typhoon events from 2013 to 2017 in Fuzhou, Southeast China. The total correlation between delta H-2 and delta O-18 is obtained as delta H-2 = 7.41 delta O-18 + 0.81 (R-2 = 0.96, N = 220). All the eight typhoon events reveal a similar variability pattern in delta(18)Ovalues which can be divided into three stages. More positive delta O-18 values occur in the first and third stages, while the second stage is dominated by most negative delta O-18 values, exhibiting an inverted U-shaped pattern. The positive delta O-18 values during the first and third stages are governed by re-evaporation. The precipitation during the second stage has distinctly lower delta O-18 values than the weighted average delta O-18 of summer precipitation in Fuzhou. Some of these values are slightly lower than those of the water vapor over the Pacific Ocean's surface. No significant relationship is observed between precipitation delta O-18 and temperature as well as the amount of precipitation during the second stage. We hypothesize that the significant O-18-depletion is mainly caused by the 'rain shield effect', which refers to combination of large-scale convection, high condensation efficiency, and recycling of isotopically depleted vapor in rain shield areas leading to very negative delta O-18 values during typhoo