Analysis of Soil Moisture Change Characteristics and Influencing Factors of Grassland on the Tibetan Plateau

Abstract

Soil moisture is an important component of the soil–vegetation–atmosphere terrestrial hydrological cycle and is an important factor affecting terrestrial ecosystems. In the context of extensive vegetation greening on the Tibetan Plateau (TP), it is important to investigate the effect of vegetation greening on soil moisture to maintain ecosystem stability and protect the sustainability of ecological restoration projects. To evaluate the effect of vegetation greening on soil moisture on the TP, the spatial distribution and trends of soil moisture and vegetation on the TP were analyzed using GIMMS NDVI data and ERA5 soil moisture data from 1982 to 2015. The effects of grassland NDVI, precipitation, and temperature on SM were also explored using multiple regression apparent and SEM. The main results are as follows: from 1982 to 2015, both grassland NDVI and SM showed a stable increasing trend. Precipitation was the most important factor influencing SM changes on the TP. In the context that vegetation greening is mainly influenced by temperature increase, vegetation plays a dominant role in SM changes in soil drying and soil wetting zones. In this paper, the climate–vegetation–soil moisture coupling mechanism of grasslands on the TP is investigated, and the related results can provide some theoretical references and suggestions for global ecosystem conservation and the sustainable development of ecological restoration projects.

Long-Term Characteristics of Surface Soil Moisture over the Tibetan Plateau and Its Response to Climate Change

“…Precipitation is the main source of moisture to the TP region, despite the fact that rising air temperature can reduce soil moisture with enhanced evapotranspiration. Precipitation's dominant role in soil moisture over the TP has also been confirmed by Wang et al [60] and Dai et al [86].…”

“…Increasing precipitation during the most recent three decades is found in most of the TP region on annual and seasonal scales [59]. Recent studies show that precipitation, not air temperature, controls soil moisture changes over the TP [60,61]. These conclusions were obtained with linear correlations, but the relationships between soil moisture and climate are nonlinear [62].…”

Revealing the Hidden Consequences of Increased Soil Moisture Storage in Greening Drylands

“…Vegetation restoration contributes to the loss of SMS by increasing vegetation transpiration and increases the input of SMS by increasing upward groundwater recharge. In locations with high precipitation, vegetation is able to sequester water, and the increase in precipitation resulting from increased vegetation cover can offset the increase in evaporation; thus, SM shows a non-significant trend [3,23]. Based on previous calculations, the precipitationsupplied vegetation growth in the BTSSR is very low [65], indicating that local precipitation cannot provide the water needed for vegetation growth.…”

“…Precipitation and shallow groundwater are the main water sources available for vegetation and usually converted into soil moisture (SM) prior to absorption and utilisation by vegetation [2]. Therefore, SM is the key hydroclimatic variable linking the biosphere, pedosphere, hydrosphere, and atmosphere [3]. SM storage (SMS) refers to the equivalent height of the water column that can be formed by the water contained in a soil layer at a specific depth, usually expressed in millimetres (mm) or centimetres (cm), which allows the water storage capacity of different soil layers to be quantified and compared.…”