Changes in rain and snow over the Tibetan Plateau based on IMERG and Ground-based observation

Abstract

The latest generation of satellite precipitation estimates, Integrated Multi-satellitE Retrievals for Global Precipitation Measurement Version 06 (IMERG V06), calibrated by monthly rain gauge data, is applied to investigate the changing characteristics of precipitation in different phases (rain, snow, and sleet) over the Tibetan Plateau (TP) from 2001 to 2020. The performance of the IMERG product in capturing the characteristics of the three precipitation phases is firstly evaluated against the ground-based observation. The results show that the IMERG product performs well in capturing the spatial distribution, magnitudes, and annual cycle of the amount and frequency of precipitation in different phases. The bias of annual precipitation amount (frequency) averaged in the 90 stations used in this study is approximately 10% (20%). Comparatively, the IMERG product shows higher skill in estimating rain than snow, and performs better in the other three seasons than in winter. In addition, the performance of the IMERG product is comparable in the southern and northern TP. Both the annual amount and frequency of precipitation have increased in most parts of the TP in the last two decades, with maximal values of 50 mm and 20 days per decade, respectively, occurring in the central part of eastern TP. Changes in the amount and frequency of precipitation are dominated by rain and snow, respectively, in the study period. In addition, light and moderate precipitation contribute approximately 70% and 90% to the increases of the regional mean precipitation amount and frequency, respectively, in the central part of eastern TP. There are no significant and uniform changes in the snowy season during the last two decades, therefore, the increase in snowy days in most areas of the TP is caused by more frequent snow events in the fairly constant snowy season.