Impacts of internal climate variability on meteorological drought changes in China

Abstract

Drought is one of the extreme events that can be caused by internal climate variability (ICV) and external forcing (EF). Here, the authors investigate the relative contributions of ICV and EF to meteorological drought changes in China using 40 members from the Community Earth System Model Large Ensemble (CESE_LE) project for historical simulations (in response to greenhouse gases and other EF) and future simulations under the RCP8.5 scenario. The authors use the Standardized Precipitation Index (SPI) to represent meteorological drought, and then define and analyze four drought parameters (frequency, severity, duration, and maximum duration) over eight regions of China. For historical periods, the ICV plays a dominant role in drought variation, while with global warming under the RCP8.5 scenario the EF becomes the prominent factor for drought characteristics. With the global warming signal, the effect of ICV varies with the drought parameters. This study suggests that the ICV should be taken into account when climate model simulations are used to investigate drought—in particular, for historical periods.

摘要

干旱受气候内部变率和外部强迫共同影响。本文利用地球系统模式CESM对历史时期和RCP8.5下的40个集合模拟的降水资料，并结合实际观测，研究了上述两因子对气象学干旱–标准化降水指数变化的贡献。通过对干旱频率、强度、持续时间、及最长持续时间的变化分析发现：在历史时期，气候内部变率对干旱变化起主要影响，而在未来（RCP8.5）情景下，外部强迫变得更为重要。本文建议，在利用模式模拟结果研究干旱变化时应考虑气候内部变率的影响。

Keywords:

• Drought
• SPI
• CESM_LE
• internal climate variability
• external forcing

关键词:

• 干旱
• 标准化降水指数
• 地球系统模式集合模拟
• 气候内部变率
• 外部强迫

Acknowledgments

We thank the CESM Large Ensemble Community Project for the datasets, obtained from https://www.earthsystemgrid.org/. Dr. Pu SHAO is also thanked for helping to download the CESM_LE data.