Key regions where land surface processes shape the East Asian climate

Hishn Chen , ,

a KLME/ILCEC/CIC-FEMD, Nanjing University of Information Science and Technology, Nanjing, China

b School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing, China

Keywords:Land surface process East Asian climate Key regions

ABSTRACT Land–atmosphere interaction, as one of the key processes affecting the atmosphere and climate over East Asia, has drawn increasing attention during the past few decades.However, the current level of understanding regarding the mechanisms through which land surface processes impact the East Asian climate needs to be improved.Based on existing studies, six key regions where land surface processes affect the East Asian climate are proposed in this study, which can provide a valuable reference for future research into land–atmosphere interaction in East Asia.

The land surface is a crucial component of the climate system, and land surface processes have long been recognized as the key to regional and even global climate.The East Asian climate is affected by the East Asian monsoon system, which is closely related to not only the oceanic forcing but also land surface processes ( Ding and Chan, 2005 ;Yasunari, 2007 ; Huang et al., 2019 ).During the past few decades, the influences of various land surface factors on the East Asian climate have received growing attention.However, due to the complexity of these processes, their impacts in this respect are not thoroughly understood.One basic scientific issue is to differentiate those regions closely related to the East Asian climate.Accordingly, based on existing studies, several key regions where land surface processes play crucial roles in modulating the East Asian climate (i.e., the Tibetan Plateau, mid–high latitudes of Eurasia, the eastern China monsoon area, the Indochina Peninsula,and the midlatitudes of East Asia and West Asia) are proposed in this article.

The Tibetan Plateau:As the largest landform in the world, the Tibetan Plateau plays a vital role in the Asian and global climate ( Ye and Gao, 1979 ; Wu et al., 2007 ; Zhao et al., 2018 ).Both the dynamic and thermodynamic forcing of the Tibetan Plateau have long been considered as vital drivers of the general circulation and climate of East Asia( Zhou et al., 2009 ; Duan et al., 2012 ; Wu et al., 2014a ; Liu et al., 2020 ).The sensible heat over this region is believed to be closely linked to summer rainfall over China ( Duan et al., 2013 ).Meanwhile, the East Asian monsoon circulation and climate are significantly affected by various land surface processes over the Tibetan Plateau, including anomalous variations in snow cover/depth ( Zhao et al., 2007 ; You et al., 2019 ),freeze–thaw processes ( Wang et al., 2020 ), soil moisture ( Yeh et al.,1984 ), and vegetation variations ( Zhang et al., 2011b ).

Mid–high latitudes of Eurasia:Snow covers most parts of the Eurasian continent in spring and winter, and it interacts strongly with the atmosphere.Eurasian winter/spring snow cover/snowmelt has been proven to exert an important influence on the East Asian winter/summer monsoon and spring/summer rainfall in eastern China ( Barnett et al.,1988 ; Chen and Sun, 2002 ; Wu et al., 2009, 2014b ; Zuo et al., 2012 ;Zhang et al., 2021 ).Meanwhile, the anomalous vegetation activity over this region can also produce significant feedbacks to local and East Asian air temperature and rainfall ( Zhou et al., 2001 ; Liu et al., 2006 ; Lee and Lee, 2020 ).

Eastern China Asian monsoon area:Controlled by the East Asian monsoon, the rainfall in eastern China shows strong variability, which tends to produce the dryness/wetness of the underlying surface.The feedback of soil moisture can also evidently influence the regional climate and the atmospheric general circulation ( Zhang et al., 2011a ,2011b ).It has been found that soil moisture is also a crucial factor that modulates the monsoon circulation and further affects summer rainfall over this region from subseasonal to interannual scales ( Zuo and Zhang, 2007 ; Zhang and Zuo, 2011 ; Dong et al., 2022 ).

Indochina Peninsula:Located upstream of the East Asian summer monsoon circulation, the Indochina Peninsula is recognized as one of the key regions affecting the monsoon system and climate ( Yang et al.,2021b ).Earlier studies have pointed out that the thermal contrast between the Indochina Peninsula and the South China Sea (SCS) can influence the onset of the SCS summer monsoon ( Zhang et al., 2002 ; Liu et al.,2010 ).More recently, investigations have suggested that spring soil wetness/dryness over this region can significantly affect the summer monsoon circulation, the western Pacific subtropical high, and rainfall in the south of China via land–atmosphere interaction and the associated anomalous surface thermal forcing ( Gao et al., 2019 ; Zhu et al., 2021 ).

Fig.1.Schematic illustration of the key regions where land surface processes shape the East Asian climate.

Against the background of global warming, the Eurasian continent exhibits strong inhomogeneous summer warming, while evidently amplified land surface warming has been detected over the midlatitudes of East Asia and West Asia ( Chen and Lu, 2014 ; Hong et al., 2017 ; Hua et al., 2021, 2022 ).Recently, the climatic effects of the anomalous thermal forcing in those two regions have received much attention.

Midlatitudes of East Asia:Accompanied by anomalous summer surface warming/cooling in the midlatitudes of East Asia, local land–atmosphere coupling has the potential to alter local circulation and affect the East Asian climate via mid–low–latitude interaction ( Chen et al.,2020 ).It has been found that nonuniform summer warming in the midlatitudes of East Asia is a major diver of the decadal weakening of extratropical cyclone activity ( Zhang et al., 2020 ; Chen et al., 2019 ), and it can further result in decadal-scale weakening of the East Asian summer monsoon though synoptic wave–mean flow interaction ( Chen et al.,2017 , 2019 ).

West Asia:The land surface thermal forcing over West Asia has been reported to exert significant local and remote effects on climate( Watanabe, 2015 ).Recent research suggests that the land surface thermal forcing related to anomalous land surface temperature variation over this region ( Song et al., 2022 ) is closely linked to the climate in North/Northeast China ( Yang et al., 2021a ).Abnormal land surface warming in spring can trigger eastward-propagating disturbances via diabatic heating.Consequently, the atmospheric circumglobal teleconnection pattern is intensified, causing anomalous circulation and climate in early summer over northern China ( Yang et al., 2021a ).

The identified key regions for the East Asian monsoon and climate in terms of land surface processes are summarized in Fig.1 .It is necessary to focus more on the land surface processes in these regions to improve our understanding of the physical mechanisms through which they affect the East Asian climate.Besides, the synergistic roles of multiple land surface variables in different key regions should be considered in the future.It is important to note that this work mainly emphasizes the biogeophysical effects of the land surface.In fact, biogeochemical processes related to the land surface and the land surface processes associated with human activity also have the potential to impact the regional climate over East Asia, which deserves further investigation.Furthermore, the key regions proposed here need to be re-examined in the future according to new knowledge in this research field.

Funding

This research was supported by the National Natural Science Foundation of China [grant numbers 42088101 and 42130609 ].