Variation of Water Conservation Function and Its Influencing Factors of Alpine Grasslands in Northern Tibet from 2000 to 2020

Abstract

With an average elevation of more than 4500 m, northern Tibet, known as the “roof of the world roof”, serves as the main body of the Qinghai-Tibetan Plateau's ecological security barrier. However, the alpine grassland ecosystem in northern Tibet has suffered considerable alterations as a result of both climate change and overgrazing, and there is a degradation trend in some regions. In 2009, one ecological engineering, the Protection and Construction Project of Ecological Security Barrier in Tibet (hereafter referred to as the “Project”) was implemented to preserve the alpine ecosystem and restore service functions in the plateau. Water conservation is one of the most important service functions in alpine grassland ecosystem in northern Tibet, where is one part of the Asian Water Tower. To clarify the specific ecological benefits of the Project, this paper utilized the InVEST model to evaluate the variation trend of the water conservation function of alpine grasslands in northern Tibet before and after the implementation of the Project from 2000 to 2020, and contribution rate of climate change and the Project was also quantified. Results showed that: (1) Although the water conservation capacity of different grassland types in northern Tibet were varied, their water conservation function all altered dramatically after implementation of the Project. Specifically, the water yield has increased by 10.07%, and the water source supply service has increased by 8.86%. Among these grasslands, the alpine meadow had the highest increasing rate, water conservation capacity increased from –1.84 mm yr–1 to 2.24 mm yr–1 Followed by the alpine desert steppe and the alpine steppe, the rate of water conservation function were decreased significantly due to the Project. (2) Although climate is still the primary factor affecting the water conservation function of alpine grasslands in northern Tibet, the Project has effectively promoted the local water conservation function, with contribution rates of 13.99%, 8.75%, and 3.71% in the alpine meadow, alpine steppe and alpine desert steppe regions respectively.