Viewing the Aridification over the Northern China during recent decades from a Historical Perspective

Abstract:

Northern China (35°-50°N; 105°-125°W) has experienced a multidecadal tendency of precipitation decrease since 1950s obviously are found in previous studies and several observational data. This aridification lasted for nearly 50 years, mainly was manifested by the precipitation decrease and the temperature increase over the northern China, and had severe influences on regional society and economics. Previous studies have suggested possible reasons and underlying physical mechanisms, which might be associated with the Pacific Decadal Oscillation (PDO), but these studies are mainly based on observational data and did not assess this aridification in a longer period. Furthermore, the contributions from anthropogenic forcings, natural forcings, and internal variability on this aridification have not been quantitatively evaluated. In this study, the Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive were used to assess this aridification from a historical perspective, and differentiate the contributions from different forcings. Compared with the aridifications found in proxy reconstructions during the last millennium, we found that the aridification during the recent decades are more intensive than most of aridifications in historical period, while, the durations and droughts are not outstandingly large. We also distinguished the effects of internal climate variabilities and external forcings through comparisons between control experiments and sensitivity experiments. The results show that it was the phase changes of PDO and the Atlantic multidecadal Oscillation (AMO) lead aridifications over the northern China to longer duration and more intensive. Under the external, especially anthropogenic forcings, resulting it outstanding from historical aridifications. The key points are that the interaction between PDO and AMO and anthropogenic influence (e.g. greenhouses gas, aerosol emission and land use cover changes) make big difference between contemporary and historical climate changes.