A model for root water uptake of alpine meadow on the Qinghai-Tibet Plateau considering soil temperature

Abstract

Predicting root water uptake (RWU) of wide-distributed alpine meadow on the Qinghai-Tibet Plateau (QTP) is essential to precisely reveal the complex hydrothermal behaviors of alpine meadow soil under warming and humidifying climate. In this study, a model for RWU of alpine meadows on the QTP is proposed, which comprehensively considers the actual root characteristics of alpine meadow and the influence of soil temperature. In the proposed model, a root density function is newly derived to describe the root characteristics of alpine meadows, where root biomass (RB) is taken as root characteristics index. Meanwhile, a temperature-dependent reduction function is developed to reflect the impact of soil temperature on the RWU of alpine meadows. The proposed model for RWU is highly competent compared to the model for RWU not considering soil temperature. Furthermore, the proposed model for RWU is applied to explore the influence of RWU effect on the water movement of soil under different soil temperatures. Results indicate that the increment of soil temperature can lead to the exponentially increasing trend for the RWU rate of alpine meadows. Under the RWU effect, the alpine meadows with the thickness of 0.25 m have contributed to the moisture redistribution of soil layer within the range of 0.75 m. At the maximum soil temperature of 23 °C, the maximum RWU rate of 25.16 × 10⁻⁹ 1/s leads to the maximum decline in volumetric water content of 6.31%. Higher soil temperature is beneficial to the stability of the shallow freeze-thaw slope covered by alpine meadows, which is the opposite of the influence of humidifying climate. It is helpful to disclose the failure mechanism of shallow freeze-thaw slopes of the QTP.