Abstract: In this paper, the linear regression analysis, Mann-Kendall test and wavelet analysis were used to analyze the variation of annual hail days in the east Hexi Corridor in China in recent 50 years based on the data of annual hail days from 1961 to 2010. Results show that there was an obvious difference in spatiotemporal distribution of annual hail days in the corridor. Spatially, the annual hail days decreased apparently from the Qilian Mountains to the corridor plain, and temporally, there was a decrease trend in overall change of annual hail days with a linear decrease rate of -0.164 3 times•a^-1. Hail occurred generally at 12:00-18:00 o’clock during the period from June to September, and its duration varied in a range of 1-20 minutes. The Mann-Kendall test was used to test the change of annual hail days in the east Hexi Corridor, the results revealed that the annual hail days started to decrease from 1985, an abrupt change occurred in 2006, and after that a significant reduction occurred. Under global climate warming, the annual hail days in the east Hexi Corridor were in a decrease trend, but such trend was delayed than the time when temperature was increased. Wavelet analysis showed that there was a 9-year quasiperiodic change in annual hail days in the east Hexi Corridor. According to the physical mechanism of occurring hail and upper and low air circulation, the largescale upper air circulation when hail weather occurred could be divided into the northwest airflow type, westerly airflow type and lowpressure through type. On which the mesoscale air circulation at 700 hPa could be further divided, and each hail type of vertical circulation and its affecting extent were analyzed.

Key words: hail, spatiotemporal distribution, climate change, air circulation situation, vertical collocate, east Hexi Corridor