09 December 2015

Changes in Moisture Flux over the Tibetan Plateau during 1979-2011: Insights from a High-Resolution Simulation-JOC-May2015


In the past three decades, the Tibetan Plateau has warmed at a faster pace than global average temperatures. The trend has already exerted major impacts on the plateau’s cryosphere and water cycle feeding major rivers that support Asia’s large population and economic development. Complex topography dominates the plateau’s climatology, but observations in the expansive region are sparse because of the harsh conditions. This motivated a team, including a scientist from the Department of Energy’s Pacific Northwest National Laboratory, to study changes in net precipitation [precipitation minus evapotranspiration (P - E)] between 1979 and 2011 using a high-resolution regional climate simulation. The team compared the high-resolution changes to those derived from both the global reanalysis that provided forcing for the regional simulation and the P – E changes from the Global Land Data Assimilation System (GLDAS) product. The net precipitation change from 1998-2011 compared to 1979-1997 exhibits general increases in the vast northwestern plateau and decreases in the southeastern plateau in all three datasets. The high-resolution simulation better resolves precipitation changes than its coarse-resolution reanalysis forcing, which contributes dominantly to the improved net precipitation change in the regional simulation compared to the global reanalysis. Hence, the former may provide better insights about what is driving the changes. The scientists explored the mechanism behind the P - E change by breaking down the column-integrated, moisture-flux convergence into thermodynamic, dynamic, and transient eddy components. High-resolution climate simulation improves the spatial pattern of net precipitation changes compared to the best available global reanalysis. High-resolution climate simulation also provides new and substantial findings regarding the role of thermodynamics and transient eddies in net precipitation changes as reflected in observed changes in major river basins fed by runoff from the plateau. The analysis reveals contrasting convergence/divergence changes between the northwestern and southeastern Tibetan Plateau and feedback through latent heat release as an important mechanism leading to the mean net precipitation changes on the plateau.

Ruby Leung

The reanalysis data used in this study are from the Research Data Archive (RDA), which is maintained by the Computational and Information Systems Laboratory (CISL) at the National Center for Atmospheric Research (NCAR). We acknowledge the Super Computing Center of Chinese Academy of Sciences for providing resources for conducting the simulations. This work is jointly supported by National Basic Research Program of China (2013CB956004), National Natural Science Foundation of China (41322033), and “100-Talent” program granted by the Chinese Academy of Sciences to Yanhong Gao and Lan Cuo. Ruby Leung is supported by the Office of Science of the U.S. Department of Energy through the Regional and Global Climate Modeling program. Pacific Northwest National Laboratory is operated for Department of Energy by Battelle Memorial Institute under Contract DE-AC05-76RL01830.