Role of Agricultural Terraces in Flood and Soil Erosion Risks Control in the High Atlas Mountains of Morocco

Terraced farming play several roles, from improving ecosystem services to enhancing associated population livelihoods. In this study, we were interested in evaluating the roles of mountain terraces in controlling floods and erosion risks, in particular in the Ourika watershed, located in the High Atlas mountains of Morocco. Rainfall simulation tests were conducted to measure infiltration, runoff and initial abstraction, while the Cesium-137 isotope technique was used to quantify soil loss. The results highlighted high infiltration for dense forests (78.00 ± 2.65 mm/h) and low for rangelands (27.12 ± 2.82 mm/h). For terraces, infiltration was found to be about 70.36 ± 0.56 mm/h, confirming the role of terraces in promoting infiltration. The runoff coefficient obtained was lowest for dense forests, followed by cultivated terraces, and highest for rangelands (62.71 ± 3.51). Thus, outside dense forests, infiltration and runoff were significantly very high and low, respectively, for agricultural terraces compared to other land use. The assessment of soil erosion rates showed a significant soil loss for rangelands compared to the agricultural terraces, further underlining the role of terraces in soil conservation. Terraces in the Ourika watershed, by increasing water infiltration, reduce the rate of surface runoff, and consequently, flood risks and soil degradation.

A diachronic study of Ourika watershed land in the High Atlas of Morocco

The Ourika watershed, located in the North-West of Moroccan High Atlas, has undergone several spatio-temporal changes and accelerated land use dynamics as a result of the interaction of climatic, topographic and anthropogenic factors. The objective of this study is to monitor the evolution of land use in the study area over the past 33 years. Landsat satellite imagery has been chosen for land cover mapping, providing a sufficient detail to identify land cover characteristics while providing more or less complete coverage of the area of action. Landsat 5 Thematic Mapper satellite images from 1987 and Landsat 8 Operational Land Imager from 2019 were used, with a spatial resolution of 30m. The images were treated and classified using Support Vector Machine algorithm (SVM) implemented on QGIS Geographic Information System software. The classification evaluation shows a Kappa coefficient of 85% and 84% and an overall accuracy of 95% and 94% for 1987 and 2019 respectively. Furthermore, the results showed a 10% decrease in the forest as well as a significant increase in the pasture, arboriculture, bare land and buildings with a respective percentage of 5.99%, 1.67%, 1.48% and 1.37% accordingly.

Measuring land losses caused by water erosion using the SWAT model in the Ourika watershed in the High Atlas of Morocco

In Morocco, the phenomena of water erosion cause significant economic losses mainly linked to the silting up of dams, the degradation of equipment and socio-economic infrastructures, the loss of soil productivity and the insecurity of the population. The SWAT (Soil and Water Assessment Tool) model was used to estimate the quantities of sediments generated by the various erosive processes at the level of the Ourika watershed. The SWAT modeling, which is done with daily time steps, used as basic data; a Digital Elevation Model GDEM-ASTER (Global Digital Elevation-Advanced Space borne Thermal Emission and Reflection Radiometer) with 30 m of resolution, a land cover map developed from the Landsat 8 OLI (Operational Land Imager) satellite image of 2017 with 30 m of resolution and a soil map published by FAO (Harmonized World Soil Database). Also, daily meteorological data from the Tensift Water Basin Agency over a period from 1992 to 2001 were used. The results obtained showed that soil losses due to water erosion in the Ourika watershed reached an average of 9.18 t.ha-1.year-1. The model was calibrated and validated using the SWAT-CUP (SWAT Calibration and Uncertainty Procedures) software SUFI-2 (Sequential Uncertainty Fitting) and after several simulations and iterations a determination coefficient R2 of 0.76 was obtained.

Assessment of Future Water Demand and Supply under IPCC Climate Change and Socio-Economic Scenarios, Using a Combination of Models in Ourika Watershed, High Atlas, Morocco

Climate change will affect the water resources system, on global and regional levels. Over the past thirty years, the High Atlas Mountains in Morocco have experienced severe droughts, which causes a decrease in water supply that affects both agriculture and the urban water system. In this paper, we assess the impact of climate change and socio-economic activities on water supply and demand in the Ourika watershed (High Atlas of Morocco), then we evaluate the efficiency and sustainability of regional adaptation strategies for water supply management. For this, we simulate and analyze the future water situation using the statistical downscaling model (SDSM) and the water assessment and planning tool (WEAP). After the model’s calibration and validation, the precipitation, minimum (Tmin) and maximum (Tmax) temperatures, water demand and unmet water demand were projected for 2100 horizon, using different climate change scenarios. The results revealed that the model’s performance, calibration and validation were found to be satisfactory. The analysis shows that the mean precipitation will decrease by 49.25% and 34.61% by 2100, under A2 and B2 emission scenarios of the Intergovernmental Panel on Climate Change (IPCC). The projected mean Tmax and Tmin will be warmer than the baseline period, with Tmax increasing by 4.2 °C (A2) and 3.6 °C (B2), and Tmin by 3.5 °C (A2) and 2.9 °C (B2) by 2100. The results also show that water demand and the unmet water demand will increase in all scenarios, the pressure on water resources will increase, leading to water scarcity. The results reveal that, under the influence of climate change, future unmet water demand is expected to reach 64 million cubic meters (MCM) by 2100. The results demonstrate that the assessments of the proposed adaptation strategies are effective, but not sufficient to ensure water sustainability for the Ourika watershed.

Cartographie Des Risques De L’erosion Hydrique Par L’equation Universelle Revisee Des Pertes En Sols, La Teledetection Et Les Sig Dans Le Bassin Versant De L’ourika (Haut Atlas, Maroc)

Covering an area of 576 square kilometers, the Ourika watershed is a sub-watershed of the large Tensift basin, located on the northwest slopes of the Marrakech High Atlas, in mid-west Morocco. This basin of dramatic topography, with sparse vegetation cover and friable substrates, is under increasing human action exacerbated by a variable and changing climate. Its vulnerability to water erosion is quite high, increasing risks of wadi flows with significant sediment loads. The aim of this work was to quantify soil loss in the basin using the Revised Universal Soil Loss Equation (RUSLE) and Geographic Information System. The results showed that the Ourika watershed was subject to strong climatic aggressiveness ranging from 55.22 to 100.57 MJ.mm/ha.h. The average soil erodibility value, K, was 0.48 t.ha.h/ha.MJ.mm, with a standard deviation of 0.28 t.ha.h/ha.MJ.mm. Slopes with values higher than 35% represented 72% of the watershed’s area, with the topographic factor, LS, values ranging from 0.01 to 94.5. The vegetation factor was high throughout the Ourika watershed while C values were higher than 0.5 for 73% of the watershed’s area. The average soil loss obtained in the basin was 380 t/ha/year. These results indicated that 48% of the watershed’s area was subject to a soil loss between 50-400 t/ha/year, and between 400 and 1000 t/ha/year for 30% of the watershed. Soil loss below the tolerance level (<7 t/ha/year) represented only 4% of the watershed area. These findings served in highlighting the significance of erosion in the Ourika watershed.