Remote sensing-based monitoring of dune mobility using the enhanced normalized difference sand index in the Middle Draa, Morocco

Abstract

Oases are complex, dynamic, and inherently fragile ecosystems. Understanding their functionality is vital for their sustainable management. This study presents findings on the spatiotemporal evolution of dune units in the Middle Draa oasis, located in southeastern Morocco. The analysis is based on the use of the Normalized Difference Enhanced Sand Index (NDESI) derived from Landsat satellite imagery (5 TM and 8 OLI). Landsat 5 TM images from 1988 and 2011, as well as Landsat 8 OLI images from 2023, were selected. Validation of the results was carried out using Corona archive images (1980), high-resolution Google Earth Pro images, and field observations. The study highlights the relevance of combining Landsat data with the NDESI index to monitor, analyze, and assess dune dynamics in arid environments. The results indicate an intensification of sand encroachment in the Middle Draa, with potential implications for ecosystems and socio-economic activities. This intensification is reflected in the concentration of 95% of dunes in the downstream part, particularly in M’hamid El Ghizlane, and a significant extension of dunes between 1988 and 2023, with an evolution rate of approximately 21 km² per year. This study provides a solid database for planning protection and environmental restoration measures, as well as for the sustainable management of sand systems in similar environments.