3.1. Precipitation, temperature, and isotopes
A unimodal distribution was exhibited by temperature and precipitation amount in 2021, respectively (Figure 2). Temperature peaked at the end of July (16.61℃) and decreased monotonically to the end of October (-6.62℃) during the sampling period. Precipitation activity was concentrated in the same period, accounting for 86.10% (465 mm) of the total annual precipitation (540 mm). Four heavy precipitation events (> 20 mm) occurred in this period, with daily precipitation amounts of 29 mm on 18 August, 24 mm on 25 July, 22 mm on 14 September, and 21mm on 15 September. The δ18O and δ2H of precipitation showed large variations, the degree of enrichment and evaporative fractionation in May and October was more than in June to September, indicating that seasonal conditions are important factors that affect the isotope characteristics of precipitation (Figure 2).