Evaluation of the GPM IMERG product in the Yarlung Zsangbo Grand Canyon of the eastern Himalaya

The Yarlung Zsangbo Grand Canyon (YGC) is one of the world's deepest canyons. In this sparsely gauged region, remotely sensed precipitation products can be valuable. A new rain gauge network was installed in the YGC in November 2018, and the observations were utilized to evaluate and calibrate the Integrated Multi‐satellite Retrieval for Global Precipitation Measurements (IMERG) precipitation product. The evaluation results demonstrate that the IMERG data reasonably captured the observed seasonal and diurnal variations in the precipitation but with much weaker seasonal and diurnal variations. IMERG underestimated the total rainfall primarily due to under-detection of rainfall events, with misses being more prevalent than false alarms. IMERG overestimated and underestimated the light and heavy precipitation, respectively, leading to a significant underestimation of the rainfall frequency and intensity at both the daily and monthly scales. The probability of detection decreased with elevation, leading to increased underestimation of rainfall events at higher elevations, and the false alarm ratio was higher in valley sites. In terms of the hit events, IMERG overestimated the light rainfall events and underestimated the heavy rainfall events and the negative bias in the hit events decreased with elevation. The GPCC calibration partially improved the underestimation of GPM, but not sufficient. This study fills the gap in IMERG validation in a complex mountainous region and has implications for users and developers.