Analysis of temporal and spatial characteristics of extreme hourly precipitation during the warm season in the Qinhe River Basin

Based on the hourly precipitation data from 10 national meteorological stations in the Qinhe River Basin in the middle reaches of the Yellow River during the warm season (May-September) from 2004 to 2023, the spatiotemporal variation characteristics in extreme hourly precipitation of thresholds, intensity, annual frequency, and contribution rates to total precipitation under the basin complex terrain during the warm season were analyzed. The spatiotemporal variation characteristics were compared with the results from data analysis utilizing information from 96 regional meteorological stations in the basin from 2018 to 2023 to verify the representativeness of the low-density national meteorological station observations of extreme precipitation.The results are as follows. (1) The spatial distribution characteristics of extreme hourly precipitation exceeding 20 mm·h⁻¹ thresholds, intensity, annual average frequency, and contribution to precipitation at national meteorological stations during the warm season, all exhibit a pattern of smaller in the middle and upper reaches than those in the lower reaches. However, the trends of change in precipitation intensity, frequency, and contribution rates are not significant. (2) The monthly variation at national meteorological stations showed an unimodal pattern, with the highest extreme hourly precipitation intensity, frequency, and contribution rate occurring in July. The diurnal variation distribution presents a bimodal pattern, with the highest frequency occurring at 09:00 BT and 13:00 BT, and the lowest frequency occurring at 01:00 BT. Little difference is found in rainfall intensity between daytime and nighttime. Extreme hourly heavy precipitation exceeding 50 mm·h⁻¹ usually occurs between June and August, with the highest frequency of occurrence in July, and the most frequent occurrences at 05:00 BT and 07:00 BT. (3) The spatial distribution and the diurnal variation of extreme hourly precipitation thresholds, intensity, and contribution rates exceeding 20 mm·h⁻¹ at regional meteorological stations are consistent with those results derived from national meteorological station data. However, the peak precipitation occurrence times of extreme hourly heavy precipitation above 50 mm·h⁻¹ differs slightly. Therefore, the long-term, low-density national meteorological station observations of extreme precipitation are representative, and can provide reliable references for extreme hourly precipitation forecasting and warning, basin climate analysis, climate feasibility studies, and other related work under the Qinhe River Basin complex terrain.