Variations in monsoon precipitation over southwest China during the last 1500 years and possible driving forces

Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the Current Warm Period—is crucial for predicting future changes to monsoon precipitation in southwest China under global warming scenarios. In this study, based on 210Pb and 137Cs dating of surface sediments and AMS 14C dating of terrestrial plant residues, we establish a robust age model that covers the last ∼1500 years (AD 439–2012) at Lake Yihai in southwest China. We use analyses of multiple geochemical proxy indices, including loss on ignition at 550°C, total organic carbon, total nitrogen, C/N ratios, and stable carbon isotopes of organic matter to reconstruct changes in summer monsoon precipitation at Lake Yihai during the last ∼1500 years. The results show that, over southwest China, warm and dry climate conditions prevailed during the MWP (AD 1000–1400) and the past 200 years, whereas conditions during the LIA (AD 1400–1800) were cold and wet. This is consistent with evidence from other geological records over southwest China, such as stalagmite and lake sediment data. Similar hydroclimatic patterns have occurred over the last 1500 years in adjacent tropical/subtropical monsoon regions where the climate is similarly dominated by the Indian summer monsoon (e.g., South China, the South China Sea, Southeast Asia, Northeast India). We suggest that the meridional migration of the mean position of the Inter-tropical Convergence Zone, and El Niño/Southern Oscillation conditions which are linked to tropical Pacific sea surface temperature, are responsible for centennial-scale hydroclimatic patterns over southwest China and adjacent areas during the last 1500 years.