Abstract:

Using the precipitation isotopic data from July 2017 to June 2018 in the mountainous area of the Kashi River Basin, in addition to the meteorological data of and precipitation in this mountainous area, we have analyzed and discussed the seasonal variation characteristics of δ¹⁸O, δD, and d-excess in precipitation, along with the relationship between δ¹⁸O and temperature and precipitation. We used a hysplit model to trace and analyze the water vapor source of atmospheric precipitation in this mountainous area. Our findings reveal that: (1) The hydrogen and oxygen isotopes in the precipitation of the Kashi River Basin fluctuate over a wide range, with obvious seasonal variation; i. e., enrichment in summer and depletion in winter. This is due to high temperatures and a strong evaporation fractionation in summer and low temperatures and a weak evaporation fractionation in winter; (2) The intercept and slope of the local meteoric water line equation in the study area are higher than are those of the global meteoric water line, indicating that the local recycled water vapor has a strong effect on high-altitude rivers. The relationship between δ¹⁸O and δD in different precipitation types is obviously different. In summer, the evaporation fractionation of δD is greater than is that of δ¹⁸O, and both the slope and the intercept of the local meteoric water line are smaller. In winter, the evaporation fractionation of δD is obviously weakened, and the slope and intercept of the snowfall local meteoric water line are both larger; (3) There is an obvious temperature effect on the isotopes of precipitation in the Kashi River Basin. In summer, the temperature is high and the isotope are enriched. The annual precipitation effect is not significant, but there is a certain precipitation effect in autumn; (4) On the annual scale, there is a relatively large surplus of deuterium, indicating that it is affected greatly by the water vapor from the Atlantic Ocean and the local recycling water vapor. In seasonal terms, the precipitation comes from the Atlantic Ocean in summer and autumn, and the deuterium surplus is high, whereas the precipitation comes from the Arctic Ocean in winter and spring, and the deuterium surplus is low; (5) In summer and autumn the precipitation comes mainly from westerly circulation and local recycled water vapor. The precipitation formed by Atlantic water vapor accounts for 68.6% of the total annual precipitation, whereas the precipitation formed by local recycled water vapor accounts for 17.1%. In winter, the precipitation is affected by westerly circulation and the Arctic air mass, and the precipitation formed by Arctic water vapor accounts for 14.3% of the total annual precipitation.

Key words: Kashi River Basin, precipitation, stable isotope, source of water vapor