δ2H and δ18O in Precipitation and Water Vapor Disentangle Seasonal Wind Directions on the Loess Plateau

In many areas of the Loess Plateau, groundwater is too deep to extract, making meteoric water (snow and rain) the only viable water resource. Here we traced the rainwater and water vapor sources using the delta H-2 and delta O-18 signature of precipitation in the northern mountainous region of Yuzhong on the Loess Plateau. The local meteoric water line in 2016 and 2017 was defined as delta H-2 = 6.8 (+/- 0.3)center dot delta O-18 + 4.4 (+/- 2.0) and delta H-2 = 7.1 (+/- 0.2)center dot delta O-18 + 1.5 (+/- 1.6), respectively. The temperature and precipitation amount are considered to be the main factor controlling the delta H-2 and delta O-18 variation of precipitation, and consequently, relationships were first explored between delta O-18 and local surface air temperature and precipitation amount by linear regression analysis. The temperature effect was significant in the wet seasons but was irrelevant in the dry seasons on daily and seasonal scales. The amount effect was significant in the wet seasons on a daily scale but irrelevant in the dry seasons. However, based on the data of the Global Network of Isotopes in Precipitation (GNIP) (1985-1987, 1996-1999) of Lanzhou weather station, the amount effects were absent at seasonal scales and were not useful to discriminate either wetter or drier seasons or even wetter or drier decades. Over the whole year, the resulting air mass trajectories were consistent with the main sources of water vapor were from the Atlantic Ocean via westerlies and from the Arctic region, with 46%, 64%, and 40% of water vapor coming from the westerlies, and 54%, 36%, and 60% water vapor from the north in spring, autumn and winter, respectively. In the summer, however, the southeast monsoon (21%) was also an important water vapor source in the Loess Plateau. Concluding, using the delta H-2 and delta O-18 signatures of precipitation water, we disentangled and quantified the seasonal wind directions that are important for the prediction of water resources for local and regional land use.

Automated summary

The study on the hydrogen and oxygen isotope characteristics of precipitation in the northern mountainous region of the Loess Plateau helps to understand the sources of rainfall and seasonal wind directions. Temperature and precipitation amount are the main factors influencing the variation of hydrogen and oxygen isotopes in precipitation.