Variability in the minimum temperature over two centuries in the overlap region between the fringe of the Asian westerly region and the temperate continental-monsoon climate transition zone

Abstract

The overlap region between the eastern fringe of the Asian westerly region and the temperate continentalmonsoon climate transition zone is sensitive to climate changes and is characterized by fragile ecosystems. It is necessary to uncover the patterns of long-term historical climate variability there. A standardized tree-ring width chronology was constructed based on the tree-ring samples collected from four representative tree species in four typical areas in the overlap region, and the 203-to 343-year annual mean minimum temperature series in the overlap region were reconstructed. The reconstructed series overlapped well with extreme climate events and low-temperature periods recorded in historical data. Therefore, the reconstructed model is stable and reliable. As suggested by the reconstructed series, the variability of annual mean minimum temperature was increasingly drastic from east to west in the overlap region, with gradually shorter periodicities. In the 19th century, the high-latitude area was in the high-temperature period, and the entire overlap region experienced signi cant low-temperature periods lasting 20-45 years till the 1950s. The western part had an earlier start time of low-temperature periods, longer cooling duration, and slower cooling rate than the central part. The overlap region experienced a signi cant warming period in approximately the last half-century, with temperature increasing faster in the western and eastern parts than in the central part. The temperature variability in the overlap region was more intense in the last two centuries, with shorter periodicities and a larger proportion of cold periods. The central and western parts of the Asian westerly region, the mid-to high-latitude regions of the transition zone, and the overlap region saw signi cantly low-temperature periods or drastic cooling trends (the Little Ice Age) in the rst half of the 19th century and signi cant warming trends under global warming afterwards. The in uences of these changes might have been exacerbated by the westerly circulation. This study not only provides new insight into the use of dendroclimatology to extract temperature series in the Asian westerly region and the transition zone but also serves as a reference for research on global climate change.