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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-147
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Tracing changes in atmospheric moisture supply to the drying Southwest China
Chi Zhang1, Qiuhong Tang1,5, Deliang Chen2, Laifang Li3, Xingcai Liu1, and Huijuan Cui4 1Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
2Regional Climate Group, Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
3Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, USA
4Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
5University of Chinese Academy of Sciences, Beijing, China
Abstract. Precipitation over Southwest China (SWC) has significantly decreased during 1979–2013. The summer months from July to September contributed the most to the decrease of precipitation. By tracing moisture sources of summer precipitation over the SWC region, it is found that most moisture originates in the monsoon region. The major moisture contributing area is divided into an extended west region, SWC, and an extended east region. The extended west region is mainly influenced by the South Asian Summer Monsoon (SASM) and the westerlies, while the extended east region is mainly influenced by the East Asian Summer Monsoon (EASM). The extended west, SWC, and extended east regions contribute 48.2 %, 15.5 %, and 24.5 % of moisture for the SWC precipitation, respectively. Moisture supply from the extended west region decreased at a rate of −23.6 mm decade−1 whereas that from the extended east increased at a rate of 4.2 mm decade−1, resulting in an overall decrease of moisture supply. Further analysis reveals that the decline of summer precipitation is mainly caused by change in the stationary component rather than the transient component of the moisture transport over the SWC region. The dynamic process (i.e. change in circulation) rather than the thermodynamic process (i.e. specific humidity) is dominant in affecting the stationary moisture transport. A prevailing easterly anomaly of moisture transport that weakened moisture supply from the Indian Ocean is to a large extent responsible for the precipitation decrease over the SWC region.

Citation: Zhang, C., Tang, Q., Chen, D., Li, L., Liu, X., and Cui, H.: Tracing changes in atmospheric moisture supply to the drying Southwest China, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-147, in review, 2017.
Chi Zhang et al.
Chi Zhang et al.

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Short summary
Precipitation over Southwest China (SWC) decreased significantly in recent years. By attributing precipitation to its sources, we found that the reduced precipitation is resulted from the reduced moisture supply from regions influenced by the South Asian Summer Monsoon and the westerlies. Further study revealed the dynamic variations in circulation dominate the interannual variations in precipitation over SWC. Changes in circulation systems may be related to the recent changes in SSTs.
Precipitation over Southwest China (SWC) decreased significantly in recent years. By attributing...
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