Assessing land degradation and quantifying its drivers in the Amudarya River delta

Abstract

Abstract The shrinking of the Aral Sea is one of the most shocking environmental disasters in the world. The Amudarya River delta (AD) is highly vulnerable to land degradation. In this research, NDVI and albedo, which represent vegetation and soil conditions, were applied in change vector analysis (CVA) to monitor land degradation. The vegetation degradation and soil exposure characteristics of land degradation were considered. Furthermore, based on boosted regression trees (BRTs), eight potential driving factors (precipitation, temperature, drought, water withdrawal, canal, livestock, salt discharge and population) were chosen to explore their relative importance to land degradation. The results revealed that some land areas have gradually degraded and fell into high land degradation in the AD, especially in the downstream areas near the Aral Sea. Soil salinization is a major consequence of high land degradation in this region. Subsequently, 920.75 km2 and 183.10 km2 of abandoned croplands were converted to sparse vegetation and grasslands, respectively. The BRT model indicated that water withdrawal availability and decreased precipitation were the most influential factors explaining the land degradation of croplands and natural vegetation from 1990 to 2000, respectively. In contrast, the salt discharge to the field plot was a major force causing land degradation of different vegetation types in the subsequent time interval (2000–2015). Because an increase in the groundwater level resulted in secondary soil salinization, a large proportion (45%) of the increased salinization occurred during this time period. Notably, due to the accelerated shrinking of the Aral Sea, some land areas surrounding the sea have fallen into high land degradation. Our findings can contribute to the implementation of the land degradation neutrality initiative to deploy restoration plans in the AD.