International Journal of Applied Earth Observation and Geoinformation 50 (2016) 64–73 Contents lists available at ScienceDirect International Journal of Applied Earth Observation and Geoinformation jo ur nal home p age: www.elsevier.com/locate/ jag Spatiotemporal monitoring of soil salinization in irrigated Tadla Plain (Morocco) using satellite spectral indices Abderrazak El Harti a,∗ , Rachid Lhissou a , Karem Chokmani b , Jamal-eddine Ouzemou a , Mohamed Hassouna c , El Mostafa Bachaoui a , Abderrahmene El Ghmari a a Team of Remote Sensing and GIS Applied to the Geosciences and the Environment, Faculty of Sciences and Techniques, PO BOX. 523, Beni Mellal, Morocco b Centre Eau Terre Environnement, INRS, 490 la Couronne, Quebec city, QC G1K 9A9, Canada c Analysis laboratory of soil, water and plant, ORMVAT, PO BOX. 244, Fkih Ben Saleh, Morocco a r t i c l e i n f o Article history: Received 15 December 2015 Received in revised form 1 March 2016 Accepted 18 March 2016 Keywords: Remote sensing TM OLI Spectral indices Soil salinity Tadla plain a b s t r a c t Soil salinization is major environmental issue in irrigated agricultural production. Conventional meth- ods for salinization monitoring are time and money consuming and limited by the high spatiotemporal variability of this phenomenon. This work aims to propose a spatiotemporal monitoring method of soil salinization in the Tadla plain in central Morocco using spectral indices derived from Thematic Mapper (TM) and Operational Land Imager (OLI) data. Six Landsat TM/OLI satellite images acquired during 13 years period (2000–2013) coupled with in-situ electrical conductivity (EC) measurements were used to develop the proposed method. After radiometric and atmospheric correction of TM/OLI images, a new soil salinity index (OLI-SI) is proposed for soil EC estimation. Validation shows that this index allowed a satisfactory EC estimation in the Tadla irrigated perimeter with coefficient of determination R 2 varying from 0.55 to 0.77 and a Root Mean Square Error (RMSE) ranging between 1.02 dS/m and 2.35 dS/m. The times-series of salinity maps produced over the Tadla plain using the proposed method show that salinity is decreasing in intensity and progressively increasing in spatial extent, over the 2000–2013 period. This trend resulted in a decrease in agricultural activities in the southwestern part of the perimeter, located in the hydraulic downstream. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Soil salinization is a major problem of land degradation and neg- atively affects plants growth (Hamzeh et al., 2013). Besides that, it is reducing the world’s irrigated area by 1–2% per year, and is becom- ing more intense in arid and semi-arid regions such as Morocco (FAO, 2002). Unfortunately, irrigated land are rapidly and strongly vulnerable to soil salinization; approximately 0.01 km 2 of fertile land are lost every minute and 30% of this loss is due to saliniza- tion (Metternicht and Zinck, 2009). In this paper, the Tadla irrigated perimeter was chosen as study area for its agricultural importance in Morocco. Increased use of saline groundwater and surface water, coupled with agricultural intensification in this perimeter leads to soil salinization and weakening of regional agricultural production (Bellouti et al., 2002; Lhissou et al., 2014). Soil salinization is a very dynamic phenomenon both in time and space, whilst com- monly used methods (field measurement, laboratory analysis) are ∗ Corresponding author. E-mail address: a.elharti@usms.ma (A. El Harti). expensive, laborious and unsuitable to the change speed of this phe- nomenon (Allbed et al., 2014; Barbouchi et al., 2015). Therefore, it became necessary to develop effective methods for mapping, moni- toring and trend analysis of soil salinization in order to take suitable and immediate mitigation decisions (Metternicht and Zinck, 2003). In this context, many studies have described the usefulness of satel- lite techniques, airborne imagery and in-situ spectroradiometry for soil salinity mapping. These techniques are promising because of the sensitivity of soil spectral response to its salt content (Farifteh et al., 2007a,b; Bannari et al., 2008; Abbas et al., 2013; Sidike et al., 2014). Thus, several authors have demonstrated the benefit of combining spectral indices derived from various sensors with the geochemical laboratory measurements (Dehaan and Taylor, 2002; Khan et al., 2005; Bouaziz et al., 2011; Abbas et al., 2013; Hamzeh et al., 2013; Allbed et al., 2014). However, there are very few stud- ies on spatiotemporal monitoring of soil salinization using the Soil Salinity Spectral Indices (SSSI). In this paper, an approach based on SSSI is developed for spa- tiotemporal monitoring of soil salinization in the Tadla irrigated perimeter. To achieve this purpose, the SSSI and laboratory mea- surements of electrical conductivity (EC) during the 2000–2013 http://dx.doi.org/10.1016/j.jag.2016.03.008 0303-2434/© 2016 Elsevier B.V. All rights reserved.