Tracing changes in atmospheric moisture supply to the drying
Chi Zhang1, Qiuhong Tang1,5, Deliang Chen2, Laifang Li3, Xingcai Liu1, and Huijuan Cui41Key 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
Received: 15 Feb 2017 – Accepted for review: 11 Mar 2017 – Discussion started: 17 Mar 2017
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.
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., doi:10.5194/acp-2017-147, in review, 2017.