Distributed hydrological model of the Qinghai Tibet Plateau based on the hydrothermal coupling: I: hydrothermal coupling simulation of "snow-soil-sand gravel layer" continuum

Abstract

The Qinghai-Tibet Plateau, known as the Asian Water Tower, is a typical alpine mountain area. Snow-covered permafrost and seasonally frozen soil widely exist on this plateau, profoundly affecting the water cycle process of the entire region. In addition, the Qinghai-Tibet Plateau has the characteristics of a thinner soil and a thicker underlying sand and gravel layer, forming a special snow-soil-sand gravel layer hydrothermal medium structure. To further study the water cycle mechanism of the Qinghai-Tibet Plateau, this study selected the Niyang River basin as a typical area to perform field-heat-coupling experiments in the field. Combined with the geological and climatic characteristics of the Qinghai-Tibet Plateau, a 12-layer snow-soil-sand gravel layer continuum was constructed to describe the hydro-thermal coupling model of the Qinghai-Tibet Plateau. A complete hydro-thermal coupling simulation equation and parameter calculation method are described. The model was validated using the measured results of the temperature, liquid water content, and freezing depth of the soil and gravel in the freezing and thawing period of 0-160 cm from 2016 to 2017. The mean values of the simulated R2 of the temperature of each and the moisture content during freezing and thawing were 0.91 and 0.52, respectively. The R2 of the soil freezing depth is 0.76. The results show that the model can better reflect the hydrothermal variation of stratified soil and sand gravel during freezing and thawing processes. The results show that the model has adequate applicability in the Qinghai-Tibet Plateau and can reflect the special change process of moisture and temperature of the soil and gravel during the freezing and melting processes in this area.