Environmental significance and zonal characteristics of stable isotope of atmospheric precipitation in arid Central Asia

摘要

To analyse the environmental significance and zonal characteristics of stable isotopes of precipitation in Arid Central Asia systematically, this study took the Pan-Hexi region as an example study area. A total of 1747 precipitation samples were collected from 25 sampling points from May 2013 to July 2014. The results showed that the elevation effects of delta O-18 and delta H-2 of precipitation in the Pan-Hexi region were - 0.07 parts per thousand/100 m and - 0.17 parts per thousand/100 m, respectively. However, the elevation effects of delta O-18 and delta H-2 were lower in the oasis area than the mountainous section of the study area. The temperature effect was significant in the oasis area when the temperature was 10 degrees C and 15 degrees C, but it was only significant in the mountain area when the temperature was 0 degrees C. The evaporation rate of falling raindrops (f) and the enrichment rate (E) were significantly higher in the oasis area (E: 34.87%; f: 20%) than in the mountain area (E: 20.56%; f: 11.71%), and the E and f values showed a significant decreasing trend from oasis area to mountain area. Sub-cloud evaporation had a significant effect on the stable isotopes in precipitation. It was found that if f increases by 1%, E increases by 0.58% in the oasis area and by 0.86% in the mountain area. The precipitation amount effect mainly occurs during summer (June to August) in the Pan-Hexi region, especially in the oasis area. This effect was caused mainly by sub-cloud evaporation rather than by monsoon circulation. Further analysis demonstrated that when precipitation is higher, sub-cloud evaporation of falling raindrops is lower and enrichment of delta O-18 is weaker. Therefore, rainfall events with higher precipitation amounts had more depleted delta O-18 and vice versa. Thus, it can be concluded that precipitation amount effect in the study area is dominated by sub-cloud evaporation, which provides new information pertaining to the isotopic evolution of precipitation in arid regions.