The Qaidam Basin (QB) in the northeastern Tibetan Plateau held a
mega-lake system during the Pliocene. Today, the lower elevations in the
basin are hyperarid. To understand the mechanisms behind this system
change, we applied the Weather Research and Forecasting model for
dynamical downscaling of ECHAM5 global climate simulations for
present-day (PD) and mid-Pliocene (PLIO) conditions. In PLIO, the annual
water balance (∆S) of the QB is higher than that in PD, resulting from a
stronger moisture influx across the western border in winter, spring,
and autumn and a weaker moisture outflux across the eastern border in
summer. The atmospheric water transport across both borders is
influenced by the mid-latitude westerlies throughout the year. The jet
stream over the QB is stronger in PLIO in winter, spring, and autumn,
causing stronger moisture input at the basin’s western border in these
seasons. In summer, the jet strength over the QB decreases in PLIO.
Meanwhile, the East Asian Summer Monsoon (EASM) intensifies and migrates
to the Northwest, transporting moisture into the QB. Thus, the weaker
moisture output through the eastern border in summer is a combined
result of weakened jet strength and the strengthening of the EASM.
Therefore, the differences in ∆S between PLIO and PD are coupled with
changes in the mid-latitude westerlies and the EASM. Given that the
mid-Pliocene climate is an analog of the projected warm climate of the
near future, our study contributes to a better understanding of the
impacts of climate change in Central Asia.