The deuterium excess (d) in precipitation, determined by the stable hydrogen and oxygen isotopes (δ²H and δ¹⁸O), is a widely applied parameter in tracing the water vapor source. Based on the multiple-year observations of stable water isotopes in precipitation at four stations in the Lanzhou city, Northwest China, we analyzed the variations in deuterium excess in precipitation at the Asian monsoon margin region. The mean value of deuterium excess at the study region is 11.0‰ in the dry season and 8.0‰ in the wet season. The d value in precipitation negatively correlates with air temperature and vapor pressure. The low d value during the wet season reflects the monsoon moisture transported from long distances. During the dry season, the continental air masses correspond to the higher d value in precipitation. The moisture regimes based on reanalysis data are generally consistent with the findings using a stable isotopic approach, and the monsoon moisture is highlighted in summer precipitation at these monsoon margin sites.

The stable isotopes in precipitation provide a new understanding for the mechanism study of water cycles in the Loess Plateau. However, there has never been an introduction for the Tianshui area, which is transitioning from semi-humid to semi-arid. We analyzed the time series changes of stable isotopes in precipitation at seven sampling points during pre-monsoon, monsoon and post-monsoon periods (April to October) in the Tianshui area. The results show that the temperature effect not only shows spatial differences but also seasonal changes and a weak precipitation effect is only found during the monsoon period. At the same time, the variation characteristics of precipitation isotopes before and after the monsoon clearly record the advancing and retreating time of the monsoon. We captured this important time node around 7 May and 21 September. Due to the influence of the regional microclimate formed by different natural conditions, the kinetic fractionation effect of isotopes in precipitation cause obvious differences in the slope and intercept of the meteoric water line in different natural regions, which shows that the stable isotopes in precipitation with high-resolution changes in a short period of time are of great significance to deeply explore the hydrological process of regional microclimates.