Abstract
Desertification is an environmental problem worldwide. Remote sensing data and technique offer substantial information for mapping and assessment of desertification. Desertification is one of the most serious forms of environmental threat in Morocco, especially in the oases in the south-eastern part of the country. This study aims to map the degree of desertification in middle Draa Valley in 2017 using a Sentinel-2 MSI (multispectral instrument) image. Firstly, three indices, namely, tasselled cap brightness (TCB), greenness (TCG) and wetness (TCW) were extracted using the tasselled cap transformation method. Secondly, other indices, such as normalized difference vegetation index (NDVI) and albedo, were retrieved. Thirdly, a linear regression analysis was performed on NDVI–albedo, TCG–TCB and TCW–TCB combinations. Results showed a higher correlation between TCW and TCB (r = −0.812) than with that of the NDVI–albedo (r = −0.50). On the basis of this analysis, a desertification degree index was developed using the TCW–TCB feature space classification. A map of desertification grades was elaborated and divided into five classes, namely, nondesertification, low, moderate, severe and extreme levels. Results indicated that only 6.20% of the study area falls under the nondesertification grade, whereas 26.92% and 32.85% fall under the severe and extreme grades, respectively. The employed method was useful for the quantitative assessment of desertification with an overall accuracy of 93.07%. This method is simple, robust, powerful, and easy to use for the management and protection of the fragile arid and semiarid lands.
Highlights
Desertification is a form of land degradation in arid, semiarid and dry sub-humid regions caused by a combination of various factors, such as climatic variations and human activities [1]
The range values of the surface albedo vary between −0.07 and 0.46; the low values correspond to the vegetation coverage and water bodies; and the high values of albedo and tasselled cap brightness (TCB) present the bright soils with the whitish colour
On the basis of the correlation analysis of the indicators of soil moisture and other indicators, a desertification degree model was constructed in a TCW–TCW feature space to construct a map of different desertification grades of lands in the Middle Draa Valley
Summary
Desertification is a form of land degradation in arid, semiarid and dry sub-humid regions caused by a combination of various factors, such as climatic variations and human activities [1]. The aridity of climate, vulnerability to soil erosion, human pressure and overexploitation of natural resources in rural areas are the main driving forces of desertification in Morocco [5]. The Tafilalet and Draa Valleys, which are located in the south-eastern part of Morocco, are mostly affected by desertification caused by soil and water salinities, sand dune encroachment, water erosion, migration and severe climate conditions [6]. The main characteristics of the Draa Valley include water and soil salinities, scarcity and variability of precipitation, intense evaporation and inadequate human activities. These characteristics result in low vegetation coverage, thereby contributing to the deterioration of an already fragile ecosystem
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