Variations in precipitation isotopes from daily to muiti-annual scales in Beijing, China

Stable isotopes of hydrogen and oxygen are effective natural tracers of precipitation processes, and their ratio variations can reflect the multi-scale changes in atmospheric circulation as well as the spatial differences in precipitation and water vapor structures. Beijing is located in the monsoon fringe region with significant climate fluctuations. Understanding the isotopic characteristics of precipitation at different time scales is of great significance for water cycle tracing and climate studies. Using the data from the Beijing Network of Isotopes in Precipitation (BNIP), this research presents a statistical analysis and interpretation of climatic processes at two typical monitoring stations. Isotope data from 2015 to 2024 are used to study the characteristics of precipitation isotope changes, environmental effects, and meteoric lines on the inter-annual, intra-annual(warm half-year from April to September and cold half-year from October to March), monthly, and daily time scales. The results showed that precipitation isotopes were enriched in the warm half-year and depleted in the cold half-year. The variation ranges of δ18O, δD, and d-excess decrease with lengthening time scales. The environmental effects observed at the two stations across different time scales are generally consistent. During the three time periods at the daily time scale, and during the warm half-year at the monthly time scales, there were obvious amount effects in precipitation isotopes, while under the daily and monthly time scales, there are temperature effects during the cold half-year and the whole year. The local meteoric water lines vary due to time scales, spatial locations, and seasons. At Yanqing station, the slopes and intercepts of the daily, monthly, and annual meteoric water lines during the warm half-year are smaller than those during the cold half-year. At Zhangfang station, the slopes and intercepts of the monthly precipitation line during the warm half year are larger than those during the cold half year, while the daily and annual meteoric water lines show similar trend with those from Yanqing station.