Abstract:

In this study,we analyzed the basic characteristics of water vapor isotopes in the middle reaches of the Heihe River,Gansu Province,China mainly based on water vapor d data. We used PSCF and CWT analysis for the 2012 summer months in the studied area.We identified potential steam source locations during the day and night,and connected this with backward trajectory clustering,maximum wind speed and direction analysis,atmospheric precipitation data,and vapor flux divergence.Our results showed that the slope of the moisture line in the daytime was greater than that at night,with elevated d values during the day.This suggests that local evaporation is stronger during the day than at night.The values of D and ¹⁸O in the water vapor increased every month,and were significantly elevated during the day due to the urban heat island effect.The water vapor source was complex,and the d value of the water vapor decreased throughout the summer.In June,high values reflected relatively humid conditions in the western Pacific,which were significantly affected by arctic and westerly water vapor.In July and August,the arctic vapor was steadily replaced by southeast water vapor.Surface topography and the movement of the pressure zone on the path of water vapor transport both affected the height of the backward trajectory of the water vapor.The water vapor transportation channel in the northwest direction was smooth with high wind speeds,which encourages water vapor transportation.In response to the movement of the pressure belt,the backward trajectory height of water vapor in August was higher than that in June and July.The origins of the water evaporation were mainly concentrated to the east and north of the study area,with lesser contributions from the northwest.Oases were the main source of water evaporation,followed by cities and rivers,with local evaporation being stronger during the day than at night.Indeed,most of the observed features were strengthened by warm daytime temperatures.

Key words: summer days and nights')">

summer days and nights, water vapor sources, water vapor isotope, middle reaches of Heihe River