不同时间尺度氢氧稳定同位素效应的比较: ———以长沙降水为例

The study area, Changsha, is located in the East China(27°53'~28°41'N, 111°53'~114°15'E). The climate of the study area is mild and humid, with four discernable seasons and rain and heat changing synchronically, categoried into the typical sub-tropical monsoon climate. Due to locating in the intersection of the southwest monsoon, the southeast monsoon and the westerlies, the complex process of precipitation formation under different weather or seasons, and the complicated variation characteristics of precipitation stable isotopes composition, Changsha is a prefect site to investigate the characteristics and influence mechanism of stable isotopes in precipitation in monsoon region. From January 2010 to December 2019, the precipitation samples were collected at the meteorological station of Hunan Normal University at the foot of Yuelu Mountain in Changsha. The whole sampling period consists of 10 complete natural years, with a total of 1247 daily precipitation samples collected, representing 1247 precipitation days. All water samples were analyzed using a Cavity Ring-Down Spectroscopy(CRDS) Isotopic Water Analyzer(Model 35EP, Los Gatos Research, Inc., USA) at the Meteorological and Climatic Laboratory of Hunan Normal University. Based on the observation data of stable isotopic composition(²H and¹⁸O) in precipitation and the corresponding daily mean temperature and precipitation for ten years, the relationship between δ¹⁸O and precipitation(temperature) and the variations of local meteoric water line(LMWL) were analyzed and compared through primary statistics methods under daily, monthly and annual time scales with different precipitation intensities. Our aims were either to reveal the differences of the stable isotope effects in different precipitation intensities and time scales or to enhance the understanding of the variations regularity of the stable isotopes in precipitation within the monsoon region. The results showed that the variation range of precipitation δ¹⁸O reduced with lengthening time scale in Changsha. Under the daily time scale, the amount effect was pronounced. Affected by the evaporation enrichment during the falling of raindrops, the weak rainfall events(< 5 mm/d) influenced the regression slope of δ¹⁸O-P obviously. Under the monthly and annual time scales, there was no obvious amount effect in precipitation isotopes. Under the climatic background characterized by synchrony of abundant rainfall and high temperature, a significant negative correlation was observed between precipitation δ¹⁸O and temperature under both daily and monthly time scales except cold half-year. Under the annual time scale, there was no obvious correlation between the precipitation δ¹⁸O with weighted averaged precipitation and the mean temperature. LMWL was obviously different under different time scales, seasons and precipitation intensities. Under the daily and monthly time scales, the slope and interception of the LMWL in the cold half-year were obviously smaller and larger than those in the warm half-year respectively, and they increased obviously with the increase of precipitation intensity and then remained less variable when daily and monthly precipitation intensity was less than 5 mm/d and 50 mm/mon, respectively. Under the annual time scale, the slope and interception of the LMWL in the cold half-year were larger than those in the warm half-year.