Abstract: Northwest China is an important ecological barrier in China. Clarifying the development trends and driving factors of its ecological environment is of great significance for the protection of the regional ecological environment and the construction of a new pattern of high-quality development. Based on MODIS imagery from 2000 to 2021, we used the sandification index (DI) and salinization index (SI) to construct an improved remote sensing ecological index (SA-RSEI). The Sen+Mann-Kendall analysis was employed to investigate the spatiotemporal variations of ecological environment quality in Northwest China. We further employed the Geodetector to quantify the impacts of remote sensing ecological factors and natural-social factors on the spatial and temporal differentiation of SA-RSEI. From 2000 to 2021, the SA-RSEI in Northwest China showed an upward trend, with significant increases of 15.95% and 23.94% during 2000-2005 and 2015-2019, respectively. The ecological environment quality was predominantly poor or relatively poor, accounting for more than 70% of the total area of Northwest China. The areas of good or excellent quality were concentrated in the eastern and southern regions, exhibiting a spatial pattern of “better in the east, worse in the west”. Between 2000 and 2021, areas showing obvious improvement and slight improvement in ecological environment quality in Northwest China accounted for 32.01% and 38.65%, respectively. The area showing degradation in ecological environment quality was relatively small, with obvious degradation mainly concentrated on both sides of Ili River Valley and in Guanzhong Plain. Among the driving factors, the sandification index and precipitation had the strongest explanatory power for the SA-RSEI. Social factors represented by land use type and population density had an annually increasing impact on the SA-RSEI. The interaction of different factors had a stronger explanatory power for the SA-RSEI than the single factors. This study provided valuable insights for ecological protection and management in Northwest China.

Key words: Northwest China, improved remote sensing ecological index, ecological environmental quality, Geodetector