The driving factors of grassland water use efficiency along degradation gradients on the Qinghai-Tibet Plateau, China

Abstract

Ecosystem water use efficiency (WUE) is an important parameter of carbon-water coupling, which connects the carbon cycle and water cycle. It is crucial to understand the spatial and temporal distribution of WUE in degraded grassland and its influencing factors for predicting land surf-atmosphere interactions and the dynamic changes of terrestrial ecosystems. Thus, combining the Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI), gross primary production (GPP) and evapotranspiration (ET), this study investigated the spatial and temporal variation of grassland degradation and WUE from 2001 to 2020 on the Qinghai-Tibet plateau (QTP) by Theil-Sen trend method and Mann-Kendall test, and identified the sensitivity response of grassland WUE to degradation, temperature, wind speed and precipitation within different degradation gradients by ridge regression analysis and generalized linear model. The results showed that (1) the WUE gradually decreases from southeast to northwest, and the interannual variation showed an increasing trend. The grassland degradation on the QTP gradually increases from southeast to northwest, and the grievous severe degradation (GSD) and severely degradation (SD) grassland accounted for 61.59% of the total grassland area. (2) The sensitivity of grassland WUE to temperature (γTEM) and precipitation (γPRE) were generally negative in the whole region, the opposite results were found in wind speed and degradation. (3) Temperature was the main factor affecting WUE in degraded grassland, and the growth trend of WUE becomes faster with the increase of the degree of degradation.