Spatio-temporal analyses of cropland degradation in the irrigated lowlands of Uzbekistan using remote-sensing and logistic regression modeling

Abstract

Advancing land degradation in the irrigated areas of Central Asia hinders sustainable development of this predominantly agricultural region. To support decisions on mitigating cropland degradation, this study combines linear trend analysis and spatial logistic regression modeling to expose a land degradation trend in the Khorezm region, Uzbekistan, and to analyze the causes. Time series of the 250-m MODIS NDVI, summed over the growing seasons of 2000-2010, were used to derive areas with an apparent negative vegetation trend; this was interpreted as an indicator of land degradation. About one third (161,000 ha) of the region's area experienced negative trends of different magnitude. The vegetation decline was particularly evident on the low-fertility lands bordering on the natural sandy desert, suggesting that these areas should be prioritized in mitigation planning. The results of logistic modeling indicate that the spatial pattern of the observed trend is mainly associated with the level of the groundwater table (odds = 330 %), land-use intensity (odds = 103 %), low soil quality (odds = 49 %), slope (odds = 29 %), and salinity of the groundwater (odds = 26 %). Areas, threatened by land degradation, were mapped by fitting the estimated model parameters to available data. The elaborated approach, combining remote-sensing and GIS, can form the basis for developing a common tool for monitoring land degradation trends in irrigated croplands of Central Asia.

Fig. 1

Location of study area in the Khorezm region, Uzbekistan. The region’s border coincides with the extent of irrigated land

Fig. 2

Raw and smoothed 16-day, 250 m MODIS NDVI time series of one pixel

Fig. 3

Negative vegetation trend in the Khorezm region of Uzbekistan, calculated from slope of linear trend of NDVI time series, summed over the growing seasons 2000–2010

Fig. 4

Farmers’ opinion on factors of land degradation in the Khorezm region of Uzbekistan. The percentages indicate the frequency of the farmers’ replies

Fig. 5

Risk map of land degradation in the Khorezm region of Uzbekistan. Class 1 indicates areas with the highest risk of degradation that gradually reduces to class 10. Dark violet areas represent land with negative vegetation trend, derived from trend analysis of 250 m MODIS NDVI time series