Variations Of Stable Isotope In Daily Precipitation And The Response To The ENSO Phases In Chongqing,southwest,China

The assessing and managing the risks of global climate change have been recognized as the major issues worldwide.The Working Group II Contribution to The Fifth Assessment Report of The Inter-governmental Panel on Climate Change considers that climate change refers to a change in the state of the climate that can be identified.In the Northern Hemisphere,1983–2012 was likely the warmest 30-year period of the last 1400 years.Climate change is causing permafrost warming and thawing.In addition,impacts from recent climate-related extremes,such as the atmosphere and ocean have warmed,the amounts of snow and ice have diminished,sea level has risen,and the concentrations of greenhouse gases have increased heat and waves,droughts,floods,cyclones,and wildfires,reveal significant vulnerability and exposure of some ecosystems and many human systems to current climate variability.ENSO phases are the dominant feature of climate variability with global climatic impacts and exert a significant impacts on weather and climate in the Pacific Rim region though the changes in Walker circulation.Isotope(?¹⁸O and ?D values)ratios in precipitation have been central to understanding changes in global climate and paleoclimate reconstruction as record in ice,coral,speleothems,lake varves and long-lived plants.The isotopic signature of precipitation provides valuable information about various processes associated with equilibrium and kinetic isotopic fractionation,such as atmospheric circulation patterns,evaporation and condensation processes,moisture source regions,transport trajectory and secondary evaporation during the rainfall droping from a cloud,therefore it can be used to make inferences about temperature and precipitation.This study investigates the relationship between ?¹⁸O in daily precipitation and large-scale atmospheric circulation over Chongqing,southwest China,especially those patterns associated with ITCZ convection and watervapor source.Stable isotopic variations in daily precipitation(?¹⁸O,?D and deuterium excess)of 129 samples data collected from April 2015 to September 2016 and their relationship with precipitation,temperature,as well as reanalysis data analysis based on the National Centers for Environmental Prediction-National Center for Atmospheric Research?NCEP/NCAR?of the National Oceanic and Atmospheric Administration?NOAA?was conducted.Stable isotope in precipitation is component for the understanding of changes in global climate and paleoclimate reconstruction.The slope and intercept of LMWL are related to the humidity during primary evaporation in vapor source region,as well as the temperature during the secondary evaporation as rainfall from the cloud?not Rayleigh distillation?.Deuterium excess values?d-excess?are influenced by meteorological conditions in original area of watervapor,evaporation during the vapor transportation and condensation and moisture recycling in local region.The results suggested that variations of ?¹⁸O in precipitation in Chongqing exhibit a significant seasonal variability,?¹⁸O values range from-13.11‰ to+1.81‰,While ?D varies between-96.31‰ and+28.70‰.The Local Meteoric Water Line?LMWL??D=8.25?¹⁸O+12.23,?R2=0.98,n=129?is found to be indistinguishable from the Global Meteoric Water Line?GMWL?.The slope in this case approaches the value of 8 with a little higher intercept than the GMWL.However it's not significantly different,which indicates closer association with GMWL and a water vapor moisture origin,all the plots from precipitation samples close to LMWL.In order to analyze the signifinance of the variations,the samples were separated between the monsoon?May to September?and pre-monsoon?October to April?seasons.The water line in the monsoon period can be described: ?D=8.28?¹⁸O+12.15,?R2=0.98,n=99?.The water line of precipitation during pre-monsoon seasons take the form: ?D=7.28?¹⁸O+10.05,?R2=0.90,n=30?.The pre-monsoon rainfall events seem to suggest an isotopic fractionation pattern induced by a non-equilibrium secondary evaporation during the process of falling rain.Additionly,there is a weak negative correlation between daily rainfall ?¹⁸O values with daily rainfall amount,as well as surface air temperature on inter-annual scale,?¹⁸O=-0.06P-4.19,?R2=0.12,n=30,P<0.001??¹⁸O=-0.28T+1.12,?R2=0.08,n=129,P<0.001?.The investigation showed that the relatively higher ¹⁸O-depletion inmonsoon rainfall is not related necessary to its amount,but rather to moisture source regions by the HYSPLIT model and vector wind,the moisture originates over the Bay of Bengal and South China sea in summer.We separated the summer monsoon seasons into 5 distinct stages based on the temporal variations of ?¹⁸O values.Stage 1 covered with the remain high ?¹⁸O values in May and early June.Stage 2 begin with the sudden decrease in ?¹⁸O.Stage 3 included the minimum values period,the dates of ?¹⁸O minimum values in 2015 and 2016 were 8 August and 30 June,respectively.Stage 4was characterized by relatively high precipitation ?¹⁸O.Whereas in stage 5,?¹⁸O remained relatively low and marked the return of ?¹⁸O values to the enriched state.On average,a spatial comparison of the seasonal atmospheric circulation patterns calculated though moisture transport flux with precipitation ?¹⁸O indicate Inter-Tropical Convergence Zone?ITCZ?control on inter-annual timescales.As a result,it was found that the intra-seasonal variations of ?¹⁸O in precipitation during summer seasons[May –September?MJAS?] were closely related to the changes of convection intensity and location of moisture sources in Chongqing.The average?¹⁸O values in precipitation from June to September in 2015 and 2016 are-7.05‰and-6.29‰,respectively,and there are lower values in 2015?-9.00‰?than 2016?-9.00 ‰?during stage3-5.Generally,it was observed that ?¹⁸O in daily precipitation over Chongqing is higher in 2015 MJAS El Ni?o event when conventive activity is reduced and lower in 2016 MJAS La Ni?a event when conventive activity is enhanced.This investigation is conducted to indicate that variations of stable isotope in daily precipitation is closely related to the large-scale atmospheric circulation and is rapidly responsive to the moisture source region.This is important for understanding paleoclimatic change in monsoonal Asia,as interannual variations in stable isotopes in that region have received less attention in the past.Therefore stable isotopic variations could be a significant shift of signal to indicate moisture source influenced by monsoon associated with monsoon region results from ENSO effects on atmospheric circulation.