Abstract:

The Hedong region of Gansu Province, China, is located in the convergence zone of the Qinghai-Tibet Plateau and Loess Plateau. The terrain is complex and diverse, and the altitude drop is up to 3961 m. The precipitation climate difference is obvious, and several studies have shown that the precipitation in this region exhibits different trends in recent years. This project is based on the precipitation data of 60 national meteorological stations in the Hedong region from April to September between 1973 and 2020. The temporal and spatial distributions and variation characteristics of total precipitation and precipitation of different magnitudes are analyzed using an empirical orthogonal function method, and the influence of temperature, large-scale circulation, topography, and other factors on summer half-year precipitation in different regions are investigated using a correlation analysis method. The results are as follows: (1) The western part of the Hedong region is located at the end of the East Asian monsoon region. Light rain and moderate rain account for the largest proportion of the total precipitation, and temperature changes have a significant impact on precipitation. The altitude of the Gannan Plateau and the northern mountain area is high, and the input water vapor is less. The promotion of climate warming on the local water cycle makes the precipitation tend to increase. The imported water vapor remains dominant in other regions in the western part, and the weakening of cold air activity makes the precipitation tend to decrease. (2) The eastern part of the Hedong region has a gentle terrain transition, and the precipitation is significantly affected by the East Asian monsoon. After 1998, the sea surface temperature in the Niño 3.4 area was primarily a negative anomaly. With the strengthening of the monsoon and the northward uplift of the Chinese rain belt, the precipitation in the eastern region increased. (3) The main feature of interannual variation in precipitation in the Hedong region is that all stations increase or decrease simultaneously, but an inverse variation in precipitation in the eastern and western regions easily occurs in a La Niña year. In the negative phase of PDO, the precipitation in the western region increases significantly and decreases in some stations in the eastern part. In the negative phase of AO, the precipitation in the southeast increases significantly and decreases in some stations in the western part. Different from the traditional research on precipitation climate change, this study focuses on the comparative analysis of the specific impact of temperature and large-scale circulation systems on the precipitation change in the summer half-year under different topographic characteristics at the end of the East Asian monsoon region, which will provide a new idea for predicting precipitation climate change in the monsoon region and is of great significance for coping with climate change and promoting disaster prevention and reduction.

Key words: summer half-year precipitation, the temporal and spatial variation characteristics, temperature, circulation index, Hedong region of Gansu Province