scholarly journals On the freeze–thaw cycles of shallow soil and connections with environmental factors over the Tibetan Plateau

2021 ◽  
Author(s):  
Ning Li ◽  
Lan Cuo ◽  
Yongxin Zhang
2021 ◽  
Author(s):  
Ning Li ◽  
Lan Cuo ◽  
Yongxin Zhang

Abstract Changes in the freeze–thaw cycles of shallow soil have important consequences for surface and subsurface hydrology, land–atmosphere energy and moisture interaction, carbon exchange, and ecosystem diversity and productivity. This work examines the shallow soil freeze–thaw cycle on the Tibetan Plateau (TP) using in–situ soil temperature observations in 0–20 cm soil layer during July 1982 – June 2017. The domain and layer averaged beginning frozen day is November 18 and delays by 2.2 days per decade; the ending frozen day is March 9 and advances by 3.2 days per decade; the number of frozen days is 109 and shortens by 5.2 days per decade. Altitude and latitude combined could explain the spatial patterns of annual mean freeze–thaw status well. Stations located near 0–ºC contour line experienced dramatic changes in freeze–thaw cycles as seen from subtropical mountain coniferous forest in the southern TP. Soil completely freezes from surface to 20–cm depth in 15 days while completely thaws in 10 days on average. Near–surface soil displays more pronounced changes than deeper soil. Surface air temperature strongly influences the shallow soil freeze – thaw status but snow exerts limited effects. Different thresholds in freeze–thaw status definition lead to differences in the shallow soil freeze–thaw status and multiple–consecutive–day approach appears to be more robust and reliable. Gridded soil temperature products could resolve the spatial pattern of the observed shallow soil freeze–thaw status to some extent but further improvement is needed.


2012 ◽  
Vol 4 (1) ◽  
pp. 21 ◽  
Author(s):  
Liu Hua ◽  
Niu Fu-Jun ◽  
Xu Zhi-Ying ◽  
Lin Zhan-Ju ◽  
Xu Jian

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Hao Zhang ◽  
Jian Sun ◽  
Junnan Xiong

Evapotranspiration (ET) is a key factor to further our understanding of climate change processes, especially on the Tibetan Plateau, which is sensitive to global change. Herein, the spatial patterns of ET are examined, and the effects of environmental factors on ET at different scales are explored from the years 2000 to 2012. The results indicated that a steady trend in ET was detected over the past decade. Meanwhile, the spatial distribution shows an increase of ET from the northwest to the southeast, and the rate of change in ET is lower in the middle part of the Tibetan Plateau. Besides, the positive effect of radiation on ET existed mainly in the southwest. Based on the environment gradient transects, the ET had positive correlations with temperature (R>0.85, p<0.0001), precipitation (R > 0.89, p < 0.0001), and NDVI (R > 0.75, p < 0.0001), but a negative correlation between ET and radiation (R = 0.76, p < 0.0001) was observed. We also found that the relationships between environmental factors and ET differed in the different grassland ecosystems, which indicated that vegetation type is one factor that can affect ET. Generally, the results indicate that ET can serve as a valuable ecological indicator.


2017 ◽  
Vol 419 (1-2) ◽  
pp. 349-361 ◽  
Author(s):  
Miaojun Ma ◽  
James W. Dalling ◽  
Zhen Ma ◽  
Xianhui Zhou

2007 ◽  
Vol 52 (1) ◽  
pp. 136-139 ◽  
Author(s):  
MeiXue Yang ◽  
TanDong Yao ◽  
XiaoHua Gou ◽  
Nozomu Hirose ◽  
Hide Yuki Fujii ◽  
...  

2019 ◽  
Vol 226 ◽  
pp. 16-25 ◽  
Author(s):  
Donghai Zheng ◽  
Xin Li ◽  
Xin Wang ◽  
Zuoliang Wang ◽  
Jun Wen ◽  
...  

2016 ◽  
Vol 2016 ◽  
pp. 1-7
Author(s):  
Bin Wang ◽  
Ben Niu ◽  
Xiaojie Yang ◽  
Song Gu

We examined the response of soil CO2emissions to warming and environmental control mechanisms in an alpine swamp meadow ecosystem on the Tibetan Plateau. Experimental warming treatments were performed in an alpine swamp meadow ecosystem using two open-top chambers (OTCs) 40 cm (OA) and 80 cm (OB) tall. The results indicate that temperatures were increased by 2.79°C in OA and 4.96°C in OB, that ecosystem CO2efflux showed remarkable seasonal variations in the control (CK) and the two warming treatments, and that all three systems yielded peak values in August of 123.6, 142.3, and 166.2 g C m−2 month−1. Annual CO2efflux also showed a gradual upward trend with increased warming: OB (684.1 g C m−2 year−1) > OA (580.7 g C m−2 year−1) > CK (473.3 g C m−2 year−1). Path analysis revealed that the 5 cm depth soil temperature was the most important environmental factor affecting soil CO2emissions in the three systems.


2018 ◽  
Vol 50 (1) ◽  
pp. e1439155 ◽  
Author(s):  
Huiru Jiang ◽  
Wenjiang Zhang ◽  
Yonghong Yi ◽  
Kun Yang ◽  
Guicai Li ◽  
...  

2019 ◽  
Author(s):  
Eike Reinosch ◽  
Johannes Buckel ◽  
Jie Dong ◽  
Markus Gerke ◽  
Jussi Baade ◽  
...  

Abstract. Climate change and the associated rise in air temperature have affected the Tibetan Plateau to a significantly stronger degree than the global average over the past decades. This has caused deglaciation, permafrost degradation and increased precipitation, heavily changing the water balance of this region. Surface displacement processes are likely to change as the ground continues to warm up and as such it is vital to understand both seasonal and interannual processes dynamics. The Nam Co area is well suited to studying these processes via Interferometric Synthetic Aperture Radar (InSAR) time series analysis, due to its lack of higher vegetation and relatively thin snow cover. The short revisit time of the Sentinel-1 system further reduces the risk of temporal decorrelation, making it possible to produce surface displacement models with good spatial coverage. We created three different surface displacement models to study freeze-thaw processes, seasonal sliding and linear creep. Most slopes of the area are unstable, with velocities of 8 to 17 mm yr−1, and some landforms reach velocities of up to 18 cm yr−1. The monsoonal climate accelerates those movements during the summer months through high temperatures and heavy rainfall. The fastest moving landforms, some of which have been identified as rock glaciers, do not follow this seasonal pattern of accelerated velocity in summer, instead they follow a linear sliding pattern. It is unclear if this linearity is connected to the ice content in those landforms. Flat regions at Nam Co are mostly stable on a multiannual scale but some experience subsidence, which could be caused by permafrost degradation. We observe a very clear seasonal freeze-thaw cycle in the valleys, where thawing and subsequent freezing of the active layer cause a vertical oscillation of the ground of up to a few centimeters, especially near streams and other water bodies.


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