Abstract
ABSTRACT Climate warming has induced significant changes in permafrost and seasonally frozen ground (SFG) in the Tibetan Plateau, which have complex influences on local environments. A better understanding of the impacts of soil freeze/thaw (F/T) dynamics on soil water transfer and vegetation growth is important to explore related eco-hydrological influences. We investigated soil F/T dynamics and their impacts with in-situ and satellite-based observations. Our results showed the contrasting F/T dynamics between SFG and permafrost areas. In permafrost areas, soil froze downward from the ground surface and upward from the active layer bottom with a distinct freezing zero-curtain, and minimum soil moisture occurred in the intermediate layer, but the thawing process was unidirectional. However, the vertical F/T directions were contrary in SFG areas, where soil moisture generally increased with depth and the thawing zero-curtain was distinct. The spring onset showed a positive correlation with thaw onset in permafrost areas, but such a correlation was variable in SFG areas likely depending on soil-moisture level. Our results implied that the different soil-moisture patterns and the varying vegetation response might be related to the spatially contrasting F/T dynamics, which may have different impacts on soil water transfer, and further affect the zero-curtain and vegetation phenology.
Highlights
The Tibetan Plateau (TP) has the largest areas of permafrost and seasonally frozen ground (SFG) in the mid- and low-latitude regions of the world because of its high terrain (Zhao et al 2010; Zou et al 2017)
We used in situ observations of soil temperature and moisture as well as the Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) to analyze the soil F/T dynamics in permafrost and seasonally frozen ground areas, and to investigate their potential impacts on soil-moisture migration and vegetation spring phenology
Our results showed contrasting soil F/T dynamics in SFG areas along the southern Qinghai-Tibet Railway and permafrost areas in the north
Summary
The Tibetan Plateau (TP) has the largest areas of permafrost and seasonally frozen ground (SFG) in the mid- and low-latitude regions of the world because of its high terrain (Zhao et al 2010; Zou et al 2017). The seasonally frozen depth in SFG areas is undergoing remarkable changes, and maximum frozen depth in the central TP decreased at a rate of 0.71 cm per year during the period of 1970–2000 (Zhao et al 2004). These changes in permafrost and SFG have strong influences on local ecological and hydrological processes. It is necessary to understand the soil freeze/thaw (F/T) dynamics and their interaction with environmental conditions in the TP region
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