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

Located on the southeastern margin of the Tibetan Plateau, Sygera Mountains constitutes a critical topographic feature on the northwestern flank of the water vapor channel of the Yarlung Zangbo Grand Canyon. The summer precipitation frequency in this region is substantially higher than that in surrounding mountain areas. Based on hourly precipitation data from 9 automatic meteorological stations on Sygera Mountains in the southeastern Tibetan Plateau (hereafter referred to as the TP) and hourly reanalysis data of ERA5 provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) from June to August 2016-2021, this study examines the temporal distribution characteristics of summertime hourly precipitation events and hourly heavy precipitation events over the Sygera Mountains.. Furthermore, the spatial distribution characteristics of precipitation under the influences of altitude and valley orientation are compared. The results are as follows. (1) During summer, short-duration precipitation events (lasting 1-3 hours) are the most frequent type. Summertime hourly heavy precipitation events contribute 52.6% of the total summer precipitation, primarily consisting of persistent rainfall with durations lasting more than 6 hours. Both precipitation events exhibit higher frequencies in the afternoon and evening, with precipitation amount also peaking during these periods. (2) Due to influence of elevation and the orientation of valleys, the characteristics of precipitation events vary across different regions. Precipitation amount, frequency and intensity of hourly precipitation events at mountaintop stations are higher than valley stations. The frequency of both precipitation events is higher at stations in quasi-north-south oriented valley than quasi-east-west oriented valley. The result of Composite analysis indicates that the spatial pattern of summer precipitation across Sygera Mountains is a product of synergistic thermodynamic and dynamic topographic influences. Orographic precipitation rate shows that the diurnal variations of surface saturated specific humidity and meridional wind dominate the precipitation diurnal cycle in both valleys, these factors exert a stronger effect, resulting in greater precipitation rates in quasi-north-south oriented valley compared to quasi-east-west oriented valley.