Variation Characteristics of Stable Isotopes in Precipitation and Response to Regional Climate Conditions during Pre-monsoon, Monsoon and Post-monsoon Periods in the Tianshui Area

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.