Based on daily precipitation data from 44 national meteorological stations in the southern Xinjiang and the NCEP/NCAR reanalysis data from May to September (warm season) during 1961-2020, the spatial and temporal variation characteristics of rainstorm and large-scale circulation anomalies under different decades and climatic background (warm-dry period and warm-wet period) in the southern Xinjiang were analyzed. The results show that the cumulative rainstorm days, rainstorm stations and rainstorm rainfall in the warm season of the southern Xinjiang has been increasing since 1961, but the variation trend of rainstorm intensity and the proportion of rainstorm rainfall in total precipitation was not obvious. The cumulative rainstorm days, rainstorm stations and rainstorm rainfall in the warm-wet period in the southern Xinjiang were significantly more than those in the warm-dry period, and the rainstorm intensity and the proportion of rainstorm rainfall in the total precipitation had little difference in the warm-wet period and the warm-dry period. After entering the warm-wet period, the rainstorm days and rainstorm rainfall amount increased in most stations in the southern Xinjiang (the most obvious increase was at southwest stations), but the increase extent in mountain area was smaller than that in plain. The central Asian trough, central Asian vortex and Tarim easterly low level jet were the main influencing systems for the heavy rain in the warm season in the southern Xinjiang. The heavy rain in the warm season in the southern Xinjiang was dominated by low vortex type in the warm-dry periods, and low trough type in the warm-wet periods. The easterly flow 850 hPa extended westward more obviously in the low vortex rainstorm than in the low trough rainstorm. In the circulation difference field between the warm-wet periods and the warm-dry period, the circulation anomaly in the high latitude area of the low trough rainstorm and the low vortex rainstorm showed reverse change characteristics.

The abundant water vapor supply is a necessary condition for heavy rainfall, especially in arid area with complex terrain on southern slope of the Tianshan Mountains. Based on daily precipitation at sixteen weather stations of southern slope of the Tianshan Mountains and NCEP/NCAR GDAS reanalysis data from May to September during 1981-2020, the circulation situation of rainstorms in warm season on southern slope of the Tianshan Mountains was analyzed, and the water vapor source and transport trajectory was simulated and clustered by using HYSPLIT model and cluster analysis. The results show that the rainstorms in warm season on southern slope of the Tianshan Mountains mainly occurred over the overlap area of the South Asia high pressure with double pattern, southwesterly jet (airflow) above 500 hPa, 700 hPa shear convergence and topographic force lifting of the Tianshan Mountains. Water vapor mainly came from Central Asia, the Atlantic Ocean and its coasts, the Mediterranean Sea and the Black Sea and adjacent areas, through the key areas of TKAP (Tajikistan, Kyrgyzstan, northeastern Afghanistan, northern Pakistan and northwestern India), southern and northern Xinjiang, it mainly transported into rainstorm areas by the westerly, southerly, northerly channels, respectively. The water vapor above 700 hPa and below 700 hPa over rainstorm areas mainly came from the westerly and northerly channels, respectively, and the contribution of water vapor in the key area of southern Xinjiang to rainstorms was the maximum. The water vapor from central Asia mainly transported to 700 hPa and below, the contribution to rainstorms was greater, and the damage of water vapor was more along the transport way, while the water vapor from the Atlantic Ocean and its coastal areas, the Mediterranean Sea and the Black Sea mainly transported above 700 hPa, and the contribution to rainstorms was relatively smaller. In additional, the water vapor in middle and lower troposphere came from northern and southern Xinjiang, eastern North America and Mongolia. Based on the above characteristics, a three-dimensional fine structure model of water vapor for rainstorm processes in warm season on southern slope of the Tianshan Mountains was established.

 Based on the hourly precipitation data of 10 national meteorological stations from 2012 to 2019, the diurnal variation characteristics of precipitation in different seasons in the Yili River Valley of Xinjiang were analyzed. The results are as follows: (1) The diurnal variation characteristics of cumulative hourly precipitation in the Yili River Valley showed a single peak in spring, summer and winter, and a double peak in autumn. The low value period of diurnal accumulated hourly precipitation in four seasons appeared in the afternoon (15:00-19:00), the high value period appeared in the morning (10:00-12:00) in spring, autumn and winter, and in the first half of the night in summer (22:00). (2) The diurnal variation characteristics of cumulative precipitation frequency and cumulative precipitation in the same season were similar. There were significant regional differences in spatial distribution of hourly average precipitation and peak precipitation frequency. (3) Shortduration precipitation events were the main events in four seasons in the Yili River Valley, with the highest proportion (89%) in summer and the lowest proportion (70%) in winter. Short duration precipitation events were the main contributors to total precipitation in summer, while long duration precipitation events were the main contributors to total precipitation in winter. (4) There was a close relationship between the daily circulation of precipitation and the persistence of precipitation in four seasons in the Yili River Valley. The precipitation events lasting for 2-8 hours and 1-4 hours were the main contributors to the diurnal variation of precipitation in spring and summer. Three types of precipitation events with different durations had roughly equal contributions to the diurnal variation peaks of precipitation in autumn and winter in the Yili River Valley.