Characteristics of summertime hourly precipitation over the Sygera Mountains on the southeastern Tibetan Plateau

Located on the southeastern margin of the Tibetan Plateau (TP), the Sygera Mountains represent a key topographic barrier on the northwestern flank of the water vapor channel of the Yarlung Zangbo Grand Canyon, where summer precipitation frequency is significantly higher than that in the surrounding mountainous areas. Using hourly precipitation data from nine national and regional meteorological stations in the Sygera Mountains and hourly ERA5 and ERA5-Land reanalysis data provided by ECMWF during June–August from 2016 to 2021, this study analyzes the spatiotemporal distribution characteristics of summer hourly precipitation events and hourly heavy precipitation events, compares the spatial distribution of hourly precipitation under the influence of altitude and valley orientation, and reveals the topographic effects on hourly precipitation characteristics. The results are as follows. (1) In summer, short-duration precipitation events lasting 1–3 h are the most frequent type in the Sygera Mountains, with precipitation mainly occurring during nighttime and afternoon hours. The hourly precipitation amounts exhibit three peak periods: early morning (03:00 LST), afternoon (14:00 LST), and evening (18:00 LST). (2) Hourly heavy precipitation events contribute 52.6% of the total summer precipitation and are dominated by long-duration events exceeding 6 h, characterized by high intensity, long duration, and low frequency. These heavy events also mainly occur from afternoon to evening, with a secondary peak in the early morning, and their precipitation amounts are comparable between afternoon and early morning, differing from the diurnal variation characteristics of hourly precipitation events. (3) Influenced by altitude and geographic location, significant spatial differences exist in summer hourly precipitation events across different regions of the Sygera Mountains. The precipitation amount, frequency, and intensity at the summit station are higher than those at valley stations. The quasi-north–south oriented valley is dominated by high-frequency, long-duration events, whereas the quasi-east–west oriented valley features lower-frequency events with slightly higher intensity. For hourly heavy precipitation events, valley stations exhibit longer durations than the summit station; the quasi-east–west oriented valley is characterized by high-intensity, low-frequency events, while the quasi-north–south oriented valley is dominated by low-intensity, high-frequency, and long-duration events. (4) The summer precipitation distribution over the Sygera Mountains is jointly influenced by the thermal and dynamic effects of topography, with both effects producing higher precipitation amounts in the quasi-north–south oriented valley than in the quasi-east–west oriented valley. The diurnal variations of surface saturated specific humidity and meridional wind dominate the diurnal variation characteristics of precipitation at stations in both valley orientations.