Abstract:

 Based on hail observation data from eastern Qinghai province between 1981 and 2024, this study investigated spatiotemporal variations in the frequency, diameter and duration of hail events using methods such as Mann−Kendall test and wavelet analysis. The aim was to understand the formation, development and anomaly patterns of hail in this region, thereby providing a basis for hail suppression, disaster mitigation and the safeguarding of agricultural production. The results showed that: (1) the mean annual number of hail events in eastern Qinghai province from 1981 to 2024 was 35.5. The average diameter of hail was 6.2mm, and the average duration per event was 6.9min. (2) During the study period, the annual hail frequency decreased significantly at a rate of 1.08 events per year, while the hail diameter and duration exhibited no significant trends. Hail occurrence displayed strong seasonality, with frequency, diameter and duration all peaking in July. On a diurnal scale, hail events primarily occurred in the afternoon (14:00 to 17:00), whereas the maximum hail diameter and duration were observed at 21:00. The frequency of hail events, hail diameter and duration exhibited abrupt changes in 2001, 1994 and 1984 respectively, showing periodic oscillations of 2−3 years, 5 years and 5−6 years. (3) The spatial pattern of hail frequency from 1981 to 2024 was consistent with the interdecadal distribution, both exhibiting more occurrences in the northwest and less occurrences in the southeast. Additionally, hail frequency demonstrated a significant positive correlation with altitude. In conclusion, hail activity in eastern Qinghai has shown a decreasing trend over the past 44 years, which is relatively favorable for local agricultural production. However, due to the complexity of the regional climate system, attention should still be paid to localized severe hail events.

Key words: Eastern region of Qinghai province, Hail, Change trend, Climate mutation, Periodic change