Response of vegetation cover to drought in the Qilian Mountains Region from 2001 to 2016

The Qilian Mountains are located in the arid and semi-arid areas of Northwest China, where the climate is dry with little precipitation; thus, the internal ecological environment is fragile. Global warming and economic development have an important impact on the regional ecological environment. The study of the temporal and spatial distribution characteristics and trends of fractional vegetation cover (FVC) and the response of FVC to drought can provide a basis for the improvement of the ecological environment and mitigation of drought impacts. Based on MOD13Q1 remote sensing and meteorological data, the spatial and temporal distribution characteristics and dynamic trends of FVC and standardized precipitation evapotranspiration index (SPEI), and the correlation between them, in the Qilian Mountains Region from 2001 to 2016 were calculated using the dimidiate pixel model, Thornthwaite method, trend analysis method, Hurst exponent, and correlation analysis method. From 2001 to 2016, the overall FVC in the Qilian Mountains showed an increasing trend. FVC was the lowest in 2001 and highest in 2011. Moreover, there were seasonal changes, and coverage was the highest in summer. From a spatial perspective, FVC in the Qilian Mountains was generally high in the southeast and low in the northwest, with an average annual value of 0.4522. Thus, there were regional differences, although FVC in most regions showed an increasing trend. During the past 16 years, 77.13% of the vegetation area in the Qilian Mountains improved and 22.87% degenerated. In the future, this change will likely tend to be negative rather than positive, although 28.1% of the vegetation area in the Qilian Mountains may continuously improve. However, the future trend of 49.23% of this area is uncertain at the maximum; therefore, these areas need more focus and protection. Most areas in the Qilian Mountains were in a humid state, and some areas in the middle and eastern sections were in a mild drought. The SPEIs on the 1-, 3-, 6-, and 12-month scales showed a trend of increasing aridity. Overall, the degree of drought in the Qilian Mountains showed a decreasing trend between 2001 and 2016, and the climate was developing in a better direction. On an annual scale, SPEI and FVCwere positively correlated. On a seasonal scale, summer FVC had the highest response to SPEI drought, followed by spring and fall, which indicates that the higher the significance between FVC and SPEI, the greater the response.