Multi-Index Remote Sensing Assessment of Desertification Dynamics in The Khorezm Irrigated Zone: BSI, SAVI, NDWI, And NDDI Analysis Over 2000–2018

This study presents a multi-index remote sensing assessment of desertification dynamics in the Khorezm irrigated zone of the Amu Darya Basin (59–62.5°E, 40.5–42.5°N) over the period 2000–2018, using Landsat Collection 2 Surface Reflectance imagery. Four spectral indices — the Bare Soil Index (BSI), Soil-Adjusted Vegetation Index (SAVI), Normalized Difference Water Index (NDWI), and Normalized Difference Drought Index (NDDI) — were computed annually and interpreted alongside NDVI-based Vegetation Condition Index (VCI) drought classification. BSI-based desertification status classification reveals that Critical desertification conditions (BSI > 0.20) persisted across the majority of study years, including years simultaneously classified as No drought by VCI, demonstrating that vegetation greenness recovery does not eliminate underlying soil degradation. SAVI analysis confirms that standard NDVI underestimates vegetation stress in the semi-arid Khorezm landscape by approximately 30% during drought years due to soil background reflectance contamination, with the SAVI-to-NDVI best-to-worst year ratio reaching 2.5:1 versus 1.9:1 respectively. NDWI values remain consistently negative across all years, with the most negative values paradoxically occurring in the best vegetation condition years, reflecting the spectral dominance of dense crop canopy NIR reflectance. These findings demonstrate the necessity of multi-index monitoring approaches for accurate desertification assessment in irrigated dryland systems and provide direct methodological support for the implementation of Uzbekistan's Land Degradation Road Map for 2024–2028.

BSI, desertification, Amu Darya Basin

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