Abstract:

Based on stable water isotopes in precipitation events spanning a time period of Jan. 1st, 2010 to Dec. 31st, 2012 in Changsha, meteoric water line (MWL) for different seasons were calculated, combining with stable water isotopes in precipitation events in Guangzhou, and local factors that may affect the MWL were also analyzed. The results showed as follows. (1) The MWL for the entire year was δD=857×δ18O+1855, and this equation was very close to that of the eastern monsoon region of China, especially the south of this area, suggesting same moisture origins for this area. Both slope and intercept for seasonal MWLs were decreasing, and followed the order winter, spring, autumn and summer. The moisture for Changhshas summer precipitation that transported by the southwest and southeast monsoon from Indian Ocean and the Pacific, which was showed by Hysplit in our other study, may cause the MWLs slope lower than 8. (2) The relationship between precipitation and MWL both in Changsha and Guangzhou indicated that there was no necessary linkages between precipitation and MWL, which contradicted the results from other researches. Also, temperature and humidity did not act as their influences on the ratio of fractionation effect. These results suggested that factors which affected MWL are complicated. (3) The differences of MWL between rainfall and snowfall should not be simply attributed to isotope fractionation caused by secondary evaporation under cloud occurring during rainfall was more stronger than that during snowfall. We believed that the differences in the ratio of fractionation effect during the phase transition processes of liquidvapor (precipitation) and solidvapor (snow) should be considered