Analysis On The Variation Characteristics And Influencing Factors Of Precipitation Stable Isotope In China Under Different Spatial And Temporal Scales

Climate change is one of the global hot topics.As the research on climate change always involves a long period of time and space range,traditional instrumental records can only provide a limited perspective.However,stable isotopes can expand such research in both spatial and temporal scales.It is because the close correlations between precipitation isotopes and climatic variables that stable isotopes in precipitation are often used to reconstruct past climatic information preserved in natural archives,master the fact of climatic fluctuation in time and predict the climate change in the future.In this paper,the spatial variation patterns of?¹⁸O in precipitation(?¹⁸O_p)in China were displayed,and based on the precipitation stable isotopic data at 36 stations,the correlations between?¹⁸O_p and multiple meteorological factors were analyzed by using methods of correlation analysis,cluster analysis and stepwise regression analysis.Meanwhile,based on the output data from the isotope enabled GCMs,the continuous wavelet transform was used to display the temporal variation patterns in annual?¹⁸O_p at 6 representative stations,the cross-wavelet and coherent-wavelet methods were applied to explore the impacts of temperature and precipitation amount on annual?¹⁸O_p.We finally used the daily?¹⁸O_p data at Changsha station from 2010 to 2017 to analyze the variation characteristics of?¹⁸O_p and the relationships between?¹⁸O_p with local and upstream climatic variables.The results showed that,?1?There were obvious latitude effect and altitude effect in the variation of?¹⁸O_p in China.Specifically,the values of?¹⁸O_p were relatively higher in the Southeastern of China.With the increasing of latitude,they became lower in North and Northeastern China.In addition,the lower values of?¹⁸O_p mostly concentrated in the Tibetan Plateau because of its high elevation.In the spatial distribution of the seasonality of?¹⁸O_p(??¹⁸O_p),it was in agreement with the seasonal change of temperature in the Northwestern and Northeastern of China and the northern part of the Tibetan Plateau,the average values of?¹⁸O_p were higher in the warm half-year?from April to September?than that in the cold half-year?from October to the following March?,so the??¹⁸O_p displayed positive values.While in the Southwest and Southeast of China,the seasonal changes of moisture sources had significant influence on?¹⁸O_p,the average values of?¹⁸O_p were lower in summer than that in winter,so that the??¹⁸O_p showed negative values.?2?After calculating the relationships of monthly?¹⁸O_p at 36 stations in China with seven meteorological variables including near-surface temperature,precipitation amount,atmospheric precipitable water,outgoing longwave radiation and wind speed at 500hPa,as well as with sea surface temperature anomaly in Nino 4 and southern oscillation index,we found that there were significant differences in the relations between?¹⁸O_p and the seven meteorological variables to the north and south sides of the Qinling Mountains-Huaihe River line,an important line dividing the different environmental effects on the precipitation stable isotopes in China.?3?Based on the cluster analysis,variations of isotopes in precipitation were divided into three zones in China,namely,the north zone including Northwest China and Northeast China,the central transition zone covering North China and the Tibetan Plateau,and the south zone.The dividing line between the north and central transition zones was roughly the same as that between the Northwest and Northern China,while the dividing line between the central transition zone and the south zone aligned well with the boundary of the Northern and Southern China.The meteorological variables controlling?¹⁸O_p differed among zones.The controlling factors were the temperature in the north zone,temperature and wind speed at 500hPa in the central transition zone,and wind speed at 500hPa in the south zone,respectively.Affected by different moisture sources and local climatic conditions,the slope of Local Meteoric Water Line?LMWL?at stations differ among zones.Stations with the slope of LMWL less than 8 mainly concentrated in the north zone and the central transition zone,while stations with the slope of LMWL more than 8 mostly lied in the north zone.?4?The Morlet wavelet analysis of annual?¹⁸O_p at 6 representative stations showed that it alternated in a negative and positive way in about 5 years at the 8-year-time scale in Urumchi.The ¹⁸O almost experienced three enrichment-depletion conversion at the 12-year-time scale in Qiqihaer,the average transformation time were about 8 years.The principal period of annual?¹⁸O_p in Shijiazhuang were 9 years,and¹⁸O nearly appeared four depletion-enrichment conversion under this time scale,the average transformation time were about 6 years.In Delingha,the ¹⁸O showed three enrichment-depletion conversion at the 13-year-time scale,the average transformation time were about 9 years.The ¹⁸O almost experienced five enrichment-depletion conversion at the 8-year-time scale in Kunming,the average transformation time were about 5 years.While in Hongkong,its ¹⁸O appeared seven depletion-enrichment conversion at the 6-year-time scale,the average transformation time were about 4 years.?5?There were different time-scale resonant periods and lag effect between annual?¹⁸O_p with annual average temperature and annual precipitation amount at 6representative stations.The correlations between them also had differences among stations.There were close relationships between annual?¹⁸O_p with both annual average temperature and annual precipitation amount at Urumqi and Shijiazhuang stations,but the correlation between annual?¹⁸O_p with annual precipitation amount was stronger than that with annual average temperature in Shijiazhuang.The annual average temperature exerted more significance on annual?¹⁸O_p at Delingha station.However,the annual precipitation amount was more important for the variation of annual?¹⁸O_p at Qiqihaer,Kunming and Hongkong stations.?6?At the daily scale,?¹⁸O_p exhibited a pronounced seasonal pattern of variation,with lower?¹⁸O_p in the warm half-year and higher?¹⁸O_p in the cold half-year.There were no statistically significant and consistent negative correlations between?¹⁸O_p with local temperature and precipitation amount.Whereas changes in?¹⁸O_p in Changsha responded sensitively to the variation of precipitation in the key upstream area along air mass trajectories.Year-to-year,the strongest negative lagged correlations?r'?between?¹⁸O_p and the preceding average precipitation amount varied from-0.79 to-0.63?all significant at the 0.001 level?in the warm half-year of 2010-2017.However,in the cold half-year,corresponding r'values varied from-0.79 to-0.38 that were all significant at the 0.001 level,except for the year 2012.The results emphasized the role of upstream effect in explaining the variations of stable isotopes in precipitation in Changsha.