Stable Isotope Ratios Of Typhoon Rains In Fuzhou,Southeast China,during 2013–2017

As an important part of the global water cycle,stable isotopes in modern precipitation contain rich climatic and environmental information.Stable hydrogen and oxygen isotopes(?²H and?¹⁸O)in precipitation have been widely used in studies pertaining to the hydrological cycle and climatology.Stable isotope ratios 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.Typhoon precipitation is conspicuous in southeastern China,but little is known about the characteristics of the stable isotopes in these heavy rainfall events.It is thus highly need to study the variation and controlling factors of the stable isotopes in extreme precipitation events.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?²H and?¹⁸O data are collected for eight typhoon events from 2013–2017 in Fuzhou,Southeast China.The major objectives are?1?to investigate the intra-event variability of precipitation stable isotopes during typhoon events;?2?to examine the influence of meteorological parameters at the sampling site on precipitation stable isotopes;and?3?to explore the factors impacting significant¹⁸O-depletion in the rain during typhoon events.The ?²H and?¹⁸O values of all typhoon precipitation samples vary greatly from-10‰to-122‰and from-2.6‰to-17‰,respectively The total correlation between?²H and?¹⁸O is obtained as?²H=7.41×?¹⁸O+0.81?R²=0.96,N=220?.Both the slope and intercept are slightly smaller than those of the GMWL(?²H=8×?¹⁸O+10)and the LMWL(?²H=8.84×?¹⁸O+16.94,R²=0.96,N=48).The effect of re-evaporation before and after typhoon landfall leads to smaller slope and intercept of the MWL of typhoon precipitation in Fuzhou compared to the corresponding values of the GMWL and LMWL.All the eight typhoon events reveal a similar variability pattern in?¹⁸O values which can be divided into three stages.More positive?¹⁸O values occur in the first and third stages?-2.6‰to-9.9‰;-3.3‰to-10.7‰?,while the second stage is dominated by most negative?¹⁸O values?-6.3‰to-17‰?,exhibiting an inverted U-shaped pattern.The positive?¹⁸O values during the first and third stages are governed by re-evaporation.The precipitation during the second stage has distinctly lower?¹⁸O values than the weighted average?¹⁸O of summer precipitation in Fuzhou.Some of these values are slightly lower than those of the water vapor in clouds over the Pacific Ocean's surface.No significant relationship is observed between precipitation?¹⁸O and temperature as well as the amount of precipitation during the second stage.Based on the correlation analysis between?¹⁸O and meteorological parameters,it is observed that stable isotopes of typhoon precipitation are not controlled by local meteorological variables on the ground.In addition,our results indicate that change in moisture sources may exert a negligible influence on the?¹⁸O.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?¹⁸O values during typhoon system.These findings suggest the use of stable isotope ratios as important tracers of typhoon water.