A long-term record (1995–2019) of the dynamics of land desertification in the middle reaches of Yarlung Zangbo River basin derived from Landsat data

Abstract

Widespread desertification in the middle part of the Yarlung Zangbo River (YZR) basin is threatening the sustainable development of this region. To capture this process, a method was proposed for large-scale desertification monitoring by using Landsat images from 1995 to 2019. The method used an integrated classification method combined with a hierarchical decision tree and nearest neighbor classifiers. The spatio-temporal dynamics of the desertification pattern were analyzed to assist in the detection of possible driving forces. Using validation samples collected from Google Earth high-resolution images and field investigations, the overall accuracy of the classification in 2019 was 92.3% with a Kappa coefficient of 0.84. The major results were: (1) total sandy land area in 2019 was 734.1 km2, which accounted for 3.7% of the study area, prominently distributed along the wide river valleys and inlets of tributaries with a strip and discontinuous pattern. Sandy land tends to be distributed in the southern aspect regions with lower elevations and that are closer to rivers; (2) sandy land areas showed two temporal stages: a gradual increase of 102.4 km2 from 1995 to 2015 and a large decrease of 106.8 km2 from 2015 to 2019; (3) newly increased sandy land was distributed in the YZR Valley, while the revegetation on sandy land occurred mainly in the Lhasa River basin and some regions in the YZR Valley; and (4) increased sandy land area of 142.1 km2 was mainly distributed in the southern band of the two rivers. Correspondingly, revegetation on sandy land was more effective on the northern banks of the river valleys. These findings provide guidance for implementing vegetation recovery on sandy lands and provide important insights for maintaining sustainable development.