Abstract:

Land degradation is a critical ecological and environmental issue that threatens ecosystem stability and food security in China. As a key ecological barrier in western China， the Three-River Headwaters Region is undergoing severe land degradation， which presents significant challenges for regional ecological security and socioeconomic development. Based on field sampling， unoccupied aerial vehicle （UAV） imagery， and Landsat data， this study established a multi-source data framework for monitoring land degradation by employing random forest （RF）， support vector machine （SVM）， and classification and regression tree （CART） models. The framework was applied to monitor land degradation dynamics in the Three-River Headwaters Region over the past three decades （1993-2003， 2003-2013， and 2013-2023）， and to analyze its spatiotemporal evolution patterns. The results indicate that： 1） The integration of UAV and satellite data significantly improved the accuracy of degraded land detection. Among the models tested in this study， the RF model based on spectral and vegetation indexes and topographic features achieved the highest accuracy. Specifically， the accuracy of identifying desertified land reached 94.73% with an F1-score of 95.85%， while the accuracy of detecting degraded black soil beach land reached 90.98% with an F1-score of 95.18%. 2） From 1993 to 2023， the areas of non-degraded land and degraded black soil beach land initially increased and then decreased. The area of salinized land showed a fluctuating trend-increasing initially， then decreasing， and increasing again， while the area of desertified land continuously declined. For all degradation types， more than half of the affected areas remained in a stable state throughout the monitoring period. 3） Overall， both the severity of black soil beach degradation and desertification showed a decreasing trend， with substantial reductions in the area of severely degraded black soil land moderately desertified land. In contrast， there were only small changes in the area of mildly and moderately salinized land， but a notable decrease in the area of severely salinized land.

Key words: Three-River Headwaters Region, land degradation, unoccupied aerial vehicles, Landsat, remote sensing monitoring