1981~2020年青藏高原春季土壤湿度时空变化特征及其与高原季风的关系

Characteristics of the Spring Soil Moisture Evolution over the Tibetan Plateau from 1981 to 2020 and Its Relationship with the Plateau Monsoon

本研究利用欧洲中心ERA5再分析资料的逐日土壤湿度(土壤体积含水量)、降水量、位势高度场以及风场数据,重点分析了1981~2020年高原春季浅层(0~7 cm)土壤湿度的时空变化特征,并探讨了青藏高原土壤湿度与高原季风的关系。青藏高原春季土壤湿度西北偏干,东南部相对偏湿的分布特征。对高原春季土壤湿度进行经验正交函数(EOF)分析后发现,其第一模态呈中部与东、西部反向变化特征,该模态存在准3年(2~4年)的振荡周期,这一周期特征在2000~2010年表现的更为显著;第二模态呈南北反向分布,较好地表征高原地区气候带与下垫面覆盖状况。研究发现,高原夏季风与高原春季土壤湿度变化之间存在密切的隔季相关,高原夏季风异常变化是翌年春季土壤湿度变化的主要原因。

This study uses the daily soil moisture(soil volumetric water content), precipitation, geopotential height field,and wind field data from the European Center ERA5 reanalysis data focusing on the analysis of the shallow(0–7 cm) soil moisture of the plateau spring from 1981 to 2020. The study also determines the characteristics of the spring soil moisture evolution over the Tibetan Plateau and discusses its relationship with the plateau monsoon. The results show that the distribution characteristics of the spring soil moisture on the Tibetan Plateau are dry in the northwest and relatively wet in the southeast. The empirical orthogonal function(EOF) analysis of the spring soil moisture in the plateau shows that the first mode has the characteristics of reverse change in the middle, east, and west. This mode has a quasi 3-year(2–4 years)oscillation period, which was more pronounced from 2000 to 2010. The second mode has a north–south reverse distribution, which better characterizes the climatic zone and underlying surface coverage in the plateau area. This study identified a close inter-season correlation between the plateau summer monsoon and plateau spring soil moisture change.The abnormal change of the plateau summer monsoon is the main reason for the spring soil moisture change in the following spring.