The impacts of soil freeze/thaw dynamics on soil water transfer and spring phenology in the Tibetan Plateau

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.

Keywords

• freeze/thaw
• permafrost
• soil moisture
• tibetan plateau
• vegetation spring onset