Soil Salinity Detection and Mapping in an Environment under Water Stress between 1984 and 2018 (Case of the Largest Oasis in Africa-Morocco)

Abstract

Water stress is one of the factors controlling agricultural land salinization and is also a major problem worldwide. According to FAO and the most recent estimates, it already affects more than 400 million hectares. The Tafilalet plain in Southeastern Morocco suffers from soil salinization. In this regard, the GIS tools and remote sensing were used in the processing of 19 satellite images acquired from Landsat 4-5, (Landsat 7), (Landsat 8), and (Sentinel 2) sensors. The most used indices in the literature were (16 indices) tested and correlated with the results obtained from 25 samples taken from the first soil horizon at a constant depth of 0.20 m from the 2018 campaign. The linear model, at first, allows the selection of five better indices of the soil salinity discrimination (SI-Khan, VSSI, BI, S3, and SI-Dehni). These last indices were the subject of the application of a logarithmic model and polynomial models of degree two and four to increase the prediction of saline soil. After studies and analysis, we concluded that the second-degree polynomial model of the salinity index (SI-KHAN) is the most efficient one for detecting and mapping soil salinity in the Tafilalet oasis, with a coefficient of determination (R2) and the Nash–Sutcliffe efficiency (NSE) equal to 0.93 and 0.86, respectively. Percent bias (PBIAS) calculated for this model equal was 1.868% < 10%, and the low value of the root mean square error (RMSE) confirms its very good performance. The drought cyclicity led to the intensification of the soil salinization process and accelerated soil degradation. The standardized precipitation anomaly index (SPAI) is strongly correlated to soil salinity. The hydroclimate condition is the factor that further controls this phenomenon. An increase in salinized surfaces is observed during the periods of 1984–1996 and 2000–2005, which cover a surface of 11.50 and 24.20 km2, respectively, while a decrease of about 50% is observed during the periods of 1996–2000 and 2005–2018.

Thirty Years of Change in the Land Use and Land Cover of the Ziz Oases (Pre-Sahara of Morocco) Combining Remote Sensing, GIS, and Field Observations

“…This state of degradation was also reported in the context of an increasing salinity trend in groundwater in the Tunisian oasis [6] and in an increase in soil salinity area and a degree in all land-use types in the desert-oasis ecotone. In a current study on the Tafilalet area, Rafik et al [53] conducted a spatial-temporal analysis of soil salinity and demonstrated a highly variable and negative association with the standardized precipitation anomaly index. The arid nature of the climate of these areas is represented by temperatures (0-48 • C), irregular annual precipitations (50-150 mm), and hot-dry winds frequently violent (40-50 km/h) favor a very high average evaporation (3358 mm/year) [54].…”

“…This serious advancement of the desertified area was accompanied by a considerable reduction of cultivated areas in the study period, principally, in the Tafilalet plain. This can be explained by the less developed class of soil in this area due to the climatic factor, wind, water erosion, and lack of vegetation cover [53].…”

Clay minerals in soils and sediment as tracers of provenance: The case study of the N'fis watershed, Morocco

“…Land degradation and particularly soil erosion is severely affecting ecosystems, societies and livelihoods globally (Batunacun et al, 2019; Rafik et al, 2022; Reed et al, 2011). The loss of reservoir storage capacity owing to soil erosion is a crucial problem, mainly in semi‐arid and arid counties where water reservoirs play a key role to meet the increasing water needs (Caputo & Carcione, 2013; Ochoa et al, 2016).…”

The Impact of Groundwater Burial Depth on the Vegetation of the Dariyabui Oasis in the Central Desert

“…In particular, the groundwater level is strongly correlated with vegetation. The over-exploitation of groundwater causes a decline in the water table, leading to an accumulation of soil salts and toxins, especially in drought years, in areas of high agricultural activity and increased water stress [15][16][17][18][19][20][21][22]. In China, the relationship between vegetation and groundwater burial depth, as well as the water table, water quality, and soil, has been studied in the Tarim River [23], Hei River [24], Shiyang River Basin [25,26], Sanguang River [27], Inner Mongolia Loop [28], Loess Plateau [29], Hulunbeier in Inner Mongolia [30], Ejina [31], and Gurbantunggut Desert [32,33].…”