Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms

• There existed a “West–East” hydroclimatic dipole mode in mid-latitude Asia during the MCA and LIA.
• There existed a “North–South” precipitation dipole mode in monsoonal eastern China during the MCA and LIA.
• ENSO could have played an important role in shaping the observed spatial patterns on a multi-centennial scale.

Investigating hydroclimatic changes during key periods such as the Medieval Climate Anomaly (MCA, 1000–1300 AD) and the Little Ice Age (LIA, 1400–1900 AD) is of fundamental importance for quantifying the responses of precipitation to greenhouse gas-induced warming on regional and global scales. This study synthesizes the most up-to-date and comprehensive proxy moisture/precipitation records during the past 1000 years in China and surroundings. The proxy data collected include 34 records from arid central Asia (ACA) and 37 records from monsoonal Asia. Our results demonstrate a pattern of generally coherent regional moisture variations during the MCA and LIA. In mid-latitude Asia north of 30°N, monsoonal northern China (North China and Northeast China) was generally wetter, while ACA (Northwest China and Central Asia) was generally drier during the MCA than in the LIA (a West–East mode). The boundary between wetter northern China and drier ACA was roughly consistent with the modern summer monsoon boundary. In monsoonal China to the east of 105°E, the northern part was generally wetter, while the southern part was generally drier during the MCA than in the LIA (a North–South mode), with a boundary roughly along the Huai River at about 34°N. These spatial patterns of moisture/precipitation variations are also identified by instrumental data during the past 50 years.In order to understand the possible mechanisms related to the moisture variations during the MCA and LIA, we investigate the major SST and atmospheric modes (e.g. the El Niño/Southern Oscillation (ENSO), the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO)) which affect the moisture/precipitation variations in the study region using both the instrumental data and the reconstructed time series. It is found that the ENSO may play an important role in determining hydroclimatic variability over China and surroundings on a multi-centennial time-scale; and that the foregoing spatial patterns could be attributed to the La Niña-like (El Niño-like) condition during the MCA (LIA). In addition, AMO and NAO may also have their own contributions.