Abstract:

The Ili River Basin is the area with the highest precipitation in the Tianshan Mountains and frequently experiences heavy precipitation. Studying the fine characteristics of the precipitation at different time scales can advance meteorological forecasting and flood control. Using the hourly precipitation data from nearly 300 regional automatic stations in the Ili River Basin during the warm season (May-August) from 2010 to 2021, taking the latest generation of the Global Precipitation Measurement Mission satellite precipitation product as the initial field, and taking the actual precipitation as the observation field, this study combines the bias-corrected IMERG precipitation estimates with the rain gauge observations through optimal interpolation (OI). The probability density function-OI two-step fusion correction method yielded high-resolution (0.1°×0.1°) hourly multi-source precipitation fusion data, from which the extreme precipitation characteristics in the Ili River Basin were analyzed. The results show that: (1) extreme hourly precipitation events (22.5-38.9 mm) occur in the northern and eastern high-altitude mountainous areas of the basin, whereas the extreme precipitation intensity is stronger in the mid-altitude plain areas at 2000 m. The spatial distribution of the extreme intensity is similar to that of the extreme precipitation thresholds but exhibits a different frequency distribution; specifically, a gradual increase of frequency with altitude. (2) The diurnal variation of hourly extreme precipitation is largest in the northern part of the basin, second-largest in the Wusun Mountain area, third-largest in the eastern section, and smallest in the southern part of the basin. In contrast, the diurnal variation of extreme precipitation frequency is largest in the southern part of the basin, followed by the Wusun Mountain area, the eastern section, and the northern part. (3) The hourly extreme precipitation (EP_{1 h}) threshold ranges from 1.2 to 8.5 mm. The three-hourly extreme precipitation (EP_{3 h}) threshold is distributed similarly to that of EP1h, showing a gradual decrease from the mid-altitude area to the high-altitude mountainous area of the basin. The thresholds of the EP_{6 h} and EP_{12 h} gradually decrease from 2000 m and 3000 m to the high-altitude areas.

Key words: multi-source precipitation fusion data, hourly extreme precipitation, spatial and temporal distribution characteristic, Yili River Basin