Revisiting the variations of precipitation and water vapour budget over the Tibetan Plateau

Abstract

Owing to the scarcity of observation data in the western Tibetan Plateau (TP), the knowledge of precipitation changes over the entire plateau based only on the limited data in eastern TP is not reliable. Therefore, the alternative high-resolution precipitation data of the China Meteorological Forcing Dataset (CMFD) are used for the comprehensive analysis of precipitation changes over the whole TP (including western and northern TP) to fill in the lack of understanding of precipitation in the western TP. Compared with observations, CMFD can broadly capture the spatial distributions and identify the temporal variabilities of precipitation over the TP. Results with CMFD data suggested that the annual precipitation over the whole TP did not show a uniform humidification trend in 1979–2018 and featured wetting and drying trends in the northern (NTP) and southern TP (STP), respectively. Additionally, the four seasonal regimes of precipitation over the northern TP (NTP, including most areas of western TP) all experienced a noticeable interdecadal shift around the late 1990s, followed by above-normal precipitation. Except for spring, the seasonal precipitation over the southern TP (STP) showed interannual variations. Spring precipitation over the STP has undergone moistening since the late 1990s, which was consistent with that over the NTP. Four different reanalysis datasets, namely JRA55, MERRA2, ERA5 and CRA40, were used to compare the water vapour budget of each boundary over the TP. The increase in spring precipitation over the NTP and STP was found to be related to the decrease in water vapour outflow from the north boundary. The interdecadal increase in summer precipitation over the NTP was mainly due to the reduction of outflow from the east boundary. Finally, the increase in autumn precipitation was related to the increase in inflow from the west boundary.