El Jazouli et al. Geosci. Lett. (2017) 4:25 DOI 10.1186/s40562-017-0091-6 LETTER Open Access Soil erosion modeled with USLE, GIS, and remote sensing: a case study of Ikkour watershed in Middle Atlas (Morocco) Aafaf El Jazouli1, Ahmed Barakat1*, Abdessamad Ghafri2, Saida El Moutaki2, Abderrahim Ettaqy3 and Rida Khellouk1 Abstract The Ikkour watershed located in the Middle Atlas Mountain (Morocco) has been a subject of serious soil erosion prob- lems. This study aimed to assess the soil erosion susceptibility in this mountainous watershed using Universal Soil Loss Equation (USLE) and spectral indices integrated with Geographic Information System (GIS) environment. The USLE model required the integration of thematic factors’ maps which are rainfall aggressiveness, length and steepness of the slope, vegetation cover, soil erodibility, and erosion control practices. These factors were calculated using remote sensing data and GIS. The USLE-based assessment showed that the estimated total annual potential soil loss was 1 1 about 70.66 ton ha− year− . This soil loss is favored by the steep slopes and degraded vegetation cover. The spectral index method, ofering a qualitative evaluation of water erosion, showed diferent degrees of soil degradation in the study watershed according to FI, BI, CI, and NDVI. The results of this study displayed an agreement between the USLE model and spectral index approach, and indicated that the predicted soil erosion rate can be due to the most rugged land topography and an increase in agricultural areas. Indeed, these results can further assist the decision makers in implementation of suitable conservation program to reduce soil erosion. Keywords: Ikkour watershed, Soil erosion, USLE, Spectral indices, GIS Introduction some extent. Tere is considerable potential for the use Soil erosion is a naturally occurring process and it is of GIS technology as an aid to soil erosion inventory with a normal geological phenomenon associated with the reference to soil erosion modeling and erosion hazard hydrologic cycle. It is a gradual process which occurs assessment. when the impact of water detaches and removes soil In Morocco, water erosion is the main cause of degra- particles causing the soil to deteriorate. Soil erosion in dation of the soil capital and the environment. It afects, catchment areas and the subsequent deposition in rivers, with varied intensities, about 40% of land in Morocco lakes, and reservoirs are of great concern for two reasons. (FAO 1990). Annual soil loss exceeds 20 ton ha−1 year−1 Firstly , the rich and fertile soil is eroded in the catchment in the Mountainous regions of northern Morocco and areas. Secondly, there is a reduction in reservoir capacity varies between 10 and 20 ton ha−1 year−1 in the pre- as well as degradation of downstream water quality. Soil Rif regions and 5 and 10 ton ha−1 year−1 in Middle and loss is the result of soil erosion. Tis, in turn, decreases High Atlas regions (MAEF 2001). In addition to soil loss, soil fertility and reduces crop yield. Soil erosion can water erosion degrades water quality and causes silting- never be stopped completely, but it can be mitigated to up of hydraulic infrastructure (Ben-Ali 2000). Tis ero- sion will only accelerate if adequate precautions are not taken early enough to address this emergency. Indeed, *Correspondence: [email protected] some scientifc research on the vulnerability to climate 1 Georesources and Environment Laboratory, Faculty of Sciences and Techniques, Sultan My Slimane University, Béni‑Mellal, Morocco change in the Mediterranean Region including Morocco Full list of author information is available at the end of the article indicates a trend toward an increasing aridity which © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. El Jazouli et al. Geosci. Lett. (2017) 4:25 Page 2 of 12 inevitably accelerates water erosion (De Ploey et al. 1991; Methods Joftic et al. 1992). In this situation, quantifcation of soil Study area loss and delineation of degraded areas is necessary for Te Ikkour watershed is located in the southwestern efective conservation planning (Yadav and Sidhu 2010). part of the Moroccan, Middle Atlas Mountain (Fig. 1), In the last decade, many scientifc works using remote at 32°32′–32°40′N and 5°50′–5°58′W, and covered an sensing and geographic information systems (GIS) tech- area of 55 km2. It is characterized by a semi-arid cli- nologies have been carried out to characterize soil erosion mate with rains frequently grouped during a few days in large areas (Haboudane et al. 2007; Rahman et al. 2009; per month. Precipitations are characterized by irregular Meusburger et al. 2010; Benzer 2010; Biswas 2012; Dabral distribution, spread irregularly from October–Novem- et al. 2008; Pandey et al. 2007; Sheikh et al. 2011). Tese ber to April–May with predominance in December, and works proved that these techniques provided very good are almost non-existent in July and August. Te mean information about eroding areas, such as soil types, litho- annual rainfall in the Oum Er Rbia Basin is 666 mm. Te logical units, and vegetation cover, with reasonable costs temperature varies between 5 and 50 °C with an average and accuracy. Integrated into GIS and remote sensing, value of 17.7 °C. Te geology of the region is dominated several models for predictive evaluation on soil erosion by the Jurassic formations. Tese formations are mainly by water have been reported in some literature (e.g., Wis- composed of limestone, dolomitic limestone, and marls chmeier and Smith 1978; Lal 2001; Fullen 2003; Merritt underlying generally Permo-Triassic formations com- et al. 2003). Universal Soil Loss Equation (USLE) is con- posed of red clays and doleritic basalts, and covered in sidered as the best model and is being used worldwide for places by Quaternary terraces. Soils and their evolution the estimation of surface erosion (e.g., Zhang et al. 2008; depend essentially on the nature of the lithological sub- Alexakis et al. 2013; Perović et al. 2013; Chatterjee et al. strates, which under the infuence of environmental fac- 2014; Kourgialas et al. 2016). Its revised version, RUSLE tors (climate, vegetation, exhibition, topography…) gives (Renard et al. 1997), became mostly used to provide esti- birth to diferent soil types. Te climate is of a continen- mates of soil loss (Demirci and Karaburun 2012; Kumar tal type. Tis site is located in mountainous areas and is et al. 2014; Ganasri and Ramesh 2015; Napoli et al. 2016; marked by a great irregularity in the amounts of precipi- Rawat et al. 2016). Other studies (Baumgardner et al. 1986; tation and a regression of vegetation cover due to human Yesou et al. 1993; Escadafal et al. 1994; Hill et al. 1994; action. Haboudane et al. 2002) have shown the interest of spectral Te Oued Ikkour that is a tributary of the Oum Er Rbia indices based on soil refectance, such as form index (FI), River crosses a distance of 15 km before reaching the coloration index (CI), brightness index (BI), and normal- Zaouit Cheikh City. It is characterized by a steep slope ized diference vegetation index (NDVI), for characterizing of ≈10° on average, an elongated shape and an index of soil surface state, especially in arid and semi-arid lands. compactness of 1.25. Te Ikkour watershed presents rug- Keeping in view of the above aspects, this study was ged terrain with the highest elevation of 2209 m. It is conducted to evaluate soil erosion rates in the Ikkour marked by a regression of forest cover due to agricultural watershed located in the high basin of the Oum Er Rbia extension, intensive pasture, and deforestation. River that sufers detrimental efects through human activities (Barakat et al. 2016). Te selected watershed Data is highly vulnerable to erosion; it constitutes one of the Te soil erosion assessment depends upon the regional main areas of Morocco, where the limestone series of characteristics of the area, namely climate, soil condition, the lower Liassic outcrop widely and show an accentu- land use/land cover, topography, and lithology. To pre- ated landform. Also, the watershed is characterized by pare maps of these characteristics, the data used in this semi-arid to sub-humid climate marked by spatial and study are collected from various sources. Te Landsat temporal rainfall variability. Tese natural factors associ- 8 OLI image with a resolution of 30 m was downloaded ated with the occupation of the soils promoted its vulner- from Earth Explorer dated June 21, 2015. It has been ability to erosion. In this regard, it became necessary to properly used for the spectral index method. Te digital quantify and map soil erosion in the Ikkour watershed. elevation model (DEM) of 30 m resolution of the study In this study, USLE and spectral index models combined area was downloaded from ASTER GDEM. It was used with GIS techniques were used to estimate soil erosion in to generate topographic parameters (slope, hydrographic the Ikkour watershed and to evaluate the spatial distribu- network). Te geological map (1:500,000) of Rabat was tion of the soil erosion-prone areas. Te results obtained used to digitize geological formations. Te monthly and by the two models were compared in order to comple- annual rainfall data from 1985 to 2014 were obtained ment each other to identify and to produce the soil ero- from the Hydraulic Basin Agency of Oum Er Rbia and sion susceptibility maps.