Abstract:Mêdog located at the entrance of the water vapor channel of the Yarlung Zangbo Grand Canyon, has the largest rainfall totals over the Tibetan Plateau. In this article, the monthly and diurnal variation characteristics of precipitation in Mêdog are analyzed with the automatic rain gauge data collected from 2019 to 2021. Based on the observations from precipitation phenomenometer and X-band dual polarization phased array radar, the evolution characteristics of two heavy precipitation events that occurred in Mêdog are explored. The results show that precipitation frequently occurs in Mêdog with rainy days exceeding 70% of the whole year and light rain less than 5 mm·h-1 as dominant rainfall type. The occurrence frequency of light rain with daily rainfall less than 10 mm is the highest, while moderate rain with daily rainfall between 10 mm and 25 mm is the largest contributor to rainfall amount. The Mêdog precipitation features obvious monthly and daily variations. The highest occurrence frequency of rainfall is in the monsoon season from June to September, which is attributed to the warm and humid airflow from the Indian Ocean. Furthermore, rainfall frequently occurs at night due to the mountain-valley wind, which is related to the valley terrain of Mêdog. In terms of the evolution of heavy rainfall events, the systematic heavy rainfall events under the effect of Tibetan Plateau vortex and South Branch Trough are characterized by expansive area and long duration. The rainfall event is dominated by small raindrop less than 2 mm, and the radar reflectivity factor is generally smaller than 35 dBz. However, local short-duration convective precipitation event forced by topographic has a wider raindrop size distribution width and higher raindrop concentration. Raindrops larger than 2 mm in diameter contribute maximum rainfall amount with radar reflectivity factor of convective core exceeding 45 dBz. The backward propagation of the storm generates a “train effect” during the heavy rainfall event of this heavy rainfall event.