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

Abstract

Stable isotope ratios (δ2H and δ18O) 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 δ2H and δ18O data are collected for eight typhoon events from 2013 to 2017 in Fuzhou, Southeast China. The total correlation between δ2H and δ18O is obtained as δ2H = 7.41 δ18O + 0.81 (R2 = 0.96, N = 220). All the eight typhoon events reveal a similar variability pattern in δ18O values which can be divided into three stages. More positive δ18O values occur in the first and third stages, while the second stage is dominated by most negative δ18O values, exhibiting an inverted U-shaped pattern. The positive δ18O values during the first and third stages are governed by re-evaporation. The precipitation during the second stage has distinctly lower δ18O values than the weighted average δ18O 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 δ18O and temperature as well as the amount of precipitation during the second stage. We hypothesize that the significant 18O-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 δ18O values during typhoon system. These findings suggest the use of stable isotope ratios as important tracers of typhoon water.