Spatiotemporal characteristics of drought and its impact on vegetation in the vegetation region of Northwest China

As one of the extreme climate events, the frequency and intensity of drought’s change significantly affect the growth of regional vegetation. Drought events have occurred frequently in the Vegetation Region of Northwest China (VRNWC) in the past 20 years, but the spatiotemporal characteristics of drought lack discussion in VRNWC. Additionally, the response mechanism of vegetation activities to drought is unclear. In this study, the Theil-Sen median trend and Mann-Kendall test correlation analysis were combined to analyse the spatiotemporal characteristics of drought in VRNWC based on the Standardized Precipitation Evapotranspiration Index (SPEI) from 2000 to 2019. Morlet wavelet and Hurst (H) exponent were used to analyse the future prediction of drought in VRNWC. The effects of drought on vegetation change were further analysed using the Normalized Difference Vegetation Index (NDVI). The results showed that from 2000 to 2019, the SPEI in VRNWC increased at the rate of 0. 0113/ a, and the drought slowed down, mainly distributed in northeastern Shaanxi, southern Gansu, southern Qilian Mountains, and western Xinjiang. However, there was extreme drought in the northwest of the Tarim Basin in 2007 and severe drought in the northern Qaidam Basin in 2014. In the past 20 years, the occurrence frequency, duration and percentage of drought grade of slight drought, moderate drought, and severe drought showed a downward trend. The VRNWC gradually developed to a wetting trend, but the overall frequency of slight drought was the highest, and the frequency of extreme drought was the lowest, while severe drought was mainly concentrated in the Qinghai Plateau. The drought in VRNWC had a periodicity of about 8a. Further, SPEIHurst indicated that the drought in the study area will probably increase in the future. Drought in VRNWC significantly impacted vegetation, and 72. 36% of the regional SPEI was positively correlated with the NDVI. This study provides a theoretical basis and data support for ecological management and future ecological restoration in vegetation regions.