Combined influences from internal variability and external forcings on megadrought events over the eastern China

Abstract:

The combined influences on the megadrought events over the eastern China from the internal variability, e.g., Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO), and external forcings, e.g., volcanic eruptions and solar radiation, and corresponding mechanisms have been investigated through a group of climate modeling and comparisons between reconstructions and simulations.

The results show that the megadroughts are usually triggered by internal climate variability within the coupled climate system, especially the PDO and AMO, because the megadroughts in the simulations are not temporally synchronous with those derived from reconstructed proxy data. While, different external forcings may contribute to frequency, magnitudes, and persistence of megadroughts through influencing the PDO and AMO. For the volcanic eruptions, composite analyses showed that, on decadal scale, the volcanic eruptions induce a negative PDO-like pattern, which does not favor the occurrence of decadal megadroughts. While, when volcanoes erupt during the megadroughts, the eruptions will intensify and extend the megadroughts. The Ming Dynasty megadrought, which has crucial influences on Chinese history, were investigated through a group of sensitivity experiments as a case study. For the solar radiation, there are significant differences in the megadrought frequencies between the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), and this difference in the megadrought frequencies is due to the nonlinear response of the precipitation variability to the large-scale atmospheric circulation patterns. Moreover, the combined influences from greenhouse gas emissions and the simultaneous PDO and AMO pattern shifts resulted in the severe aridification over eastern China during recent decades.