Timescale dependence of the relationship between the East Asian summer monsoon strength and precipitation over eastern China in the last millennium

Abstract

Abstract. Precipitation/humidity proxies are widely used to reconstruct the historical East Asian summer monsoon (EASM) variations based on the assumption that summer precipitation over eastern China is closely and stably linked to the strength of EASM. However, whether the observed EASM–precipitation relationship (e.g., increased precipitation with a stronger EASM) was stable throughout the past remains unclear. In this study, we used model outputs from the Paleoclimate Modelling Intercomparison Project Phase III and Community Earth System Model to investigate the stability of the EASM–precipitation relationship over the last millennium on different timescales. The model results indicate that the EASM strength (defined as the regionally averaged meridional wind) was enhanced in the Medieval Climate Anomaly (MCA; ∼ 950–1250 AD), during which there was increased precipitation over eastern China, and weakened during the Little Ice Age (LIA; ∼ 1500–1800 AD), during which there was decreased precipitation, consistent with precipitation/humidity proxies. However, the simulated EASM–precipitation relationship is only stable on a centennial and longer timescale and is unstable on a shorter timescale. The nonstationary short-timescale EASM–precipitation relationship broadly exhibits a multi-decadal periodicity, which may be attributed to the internal variability of the climate system and has no significant correlation to external forcings. Our results have implications for understanding the discrepancy among various EASM proxies on a multi-decadal timescale and highlight the need to rethink reconstructed decadal EASM variations based on precipitation/humidity proxies.