Soil Erosion in a Changing Environment over 40 Years in the Merguellil Catchment Area of Central Tunisia

Soil degradation and erosion in semi-arid regions can significantly impact agricultural development, environmental sustainability, and hydrological balance. Understanding the impacts of land use changes and soil and water conservation (SWC) technique implementation on soil erosion and sediment yield is critical to planning effective watershed management. This study aims to evaluate the impacts of environmental changes in the Merguellil watershed (Central Tunisia) over the last forty years. To achieve this, remote sensing techniques and a geographic information system (GIS) will be employed to classify Landsat images from 1980 to 2020. Additionally, the Revised Universal Soil Loss Equation model will be utilized to estimate soil erosion rates, while the sediment delivery distributed model will be employed for sediment yield modeling. Spatiotemporal changes in land use and land cover and in areas treated with SWC techniques were analyzed as the main factors influencing changes in erosion and sediment yield. The combined impact of land use change and SWC techniques resulted in a decrease in the annual soil erosion rate from 18 to 16 t/ha/year between 1980 and 2020 and in sediment yield from 9.65 to 8.95 t/ha/year for the same period. According to the model’s predictions, both soil erosion and sediment yield will experience a slight increase with further degradation of natural vegetation and a reduction in the efficiency of SWC works. This emphasizes the importance of continued efforts in adopting and sustaining SWC techniques, as well as preserving natural vegetation cover, to proactively combat soil degradation and its adverse effects on the environment and communities. Continuous dedication to these measures is crucial to preserving our ecosystem, promoting sustainable practices, and protecting the well-being of both the environment and society

Assessment of drought stress in arid olive groves using HidroMORE model

The olive tree is well known for being adapted to the arid conditions of the Mediterranean basin. However, prolonged drought periods which are expected to become more frequent because of climate change could result in severe water stress. In order to map the spatial distribution of drought stress in the olive groves in the arid regions of southeastern Tunisia (governorate of M denine), we made recourse to the HidroMORE model (based mainly on FAO56 ET, NDVI from Sentinel 2 images and other physical parameters) to compute the water balance in a GIS environment. The outputs were compared to in situ soil water content measurements in four selected sites representing the various agro-ecological zones (mountains, piedmont, inner plain and coast) of the study site during the observation period from January 2016 to December 2019. The model outputs performed relatively well (the overall correlation coefficient R2=0.72; index of agreement IA=0.76). The simulation results show that during normal years or average droughts, the water stress is least in the mountain and piedmont zones because of the additional runoff water supplied by the traditional water harvesting structures (Jessour and Tabias) and in the coastal zone, thanks to the higher air humidity and rainfall. In contrast, the olives in the inner plains are the most affected. Nevertheless, in case of severe droughts, the stress is generalised. Thus, the model could be used as a decision tool for prioritizing areas of intervention for drought control and mitigation (supplemental irrigation for trees safeguard, etc.)</jats:p