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

Long-Term Impact of Soil and Water Conservation Measures on Soil Erosion in a Tunisian Semi-Arid Watershed

Understanding and long-term assessment of the efficacy of soil and water conservation (SWC) techniques is essential for sustainable watershed management. There have been few studies measuring the long-term impact of SWC on soil erosion at the catchment scale due to a lack of historical data. This research aims to measure and analyze the impact of SWC interventions on sediment yield using the Soil and Water Assessment Tool (SWAT) in the Wadi Rmel watershed between 2000 and 2020. The study approach has simultaneously three main aspects: (i) long-term and temporally dynamic, (ii) large-scale landscape distribution, and (iii) empirical evidence of impacts induced by terracing measures. Historical data on SWC in 2000, 2005, 2010, 2015, and 2020 were used for running the model. The monthly calibration (2001–2014) using the SUFI2 algorithm was implemented with 22 input parameters and displayed a good model performance, with a Nash–Sutcliffe efficiency (NSE) of 0.61 for daily runoff and a coefficient of determination (R2) of 0.66. A satisfactory result was obtained for the monthly validation process (2015–2020) with NSE value equal to 0.83 and R2 value of 0.85. The result showed the increase in terracing areas led to a cumulative decrease in watershed sediment yield in long-term, i.e., the reduced erosion per one hectare of the expanded terracing area after 10–20 years were about 9–33 times higher than those in the first 5 years. This finding suggests that maximal benefits of SWC should be expected in the long-term, i.e., beyond a decade. Additionally, the study revealed variations in sediment yield contribution among sub-basins, with the southwestern region being the degradation hotspot areas (having erosion exceeding tolerable thresholds) needing prioritization for erosion controls. These findings enable stakeholders to plan effective management in semi-arid wheat-based agricultural areas with scarce data

Homogeneity and Trend Analysis of Climatic Variables in Cap-Bon Region of Tunisia

As a semi-arid Mediterranean country, Tunisia is affected by the impacts of climate change, particularly the coastal regions like the Cap-Bon. Irregular rainfall, rising temperatures and the recurrence of extreme events are all indicators that affect ecosystems and populations and make them more vulnerable to the influence of climatic variables. Therefore, an analysis of the trends of climate variables can contribute to facilitating the development of effective adaptation strategies. In this matter, this study was conducted to assess the homogeneity and trends of minimum and maximum air temperature (Tmin and Tmax) and precipitation (P) in the Cap-Bon region. Daily data were collected from the meteorological station of Nabeul for the period of 1982–2020. Pettitt and SNHT tests for homogeneity were applied to identify the breakpoints in multi-time scales of Tmax, Tmin and P data series. The Mann–Kendall (MK) test was used to detect the change in the time-series trend. A modified Mann–Kendall (mMK) test was used to remove the autocorrelation effect from the data series. Both the MK and mMK tests were used at the 5% significant level. The magnitude of the climatic trend was estimated using the non-parametric Sen’s slope estimator. Contrary to Tmin and P, the results of the homogeneity tests revealed the existence of significant breakpoints in the annual, seasonal and monthly Tmax time series. For most cases, the breakpoint occurred around the year 2000. For Tmin, significant breakpoints were recorded in March and April, while a significant shift in the P time series was detected in December. The Mann–Kendall results show a significant warming trend in annual Tmax, with magnitudes equal to 0.065 and 0.045 °C/year before and after the breakpoint, respectively. Nevertheless, non-significant tendencies were observed in the annual Tmin and P time series. On the monthly time scale, Tmax exhibited a significant upward trend in June and August, before the observed breakpoints, with Sen’s slope values equal to 0.065 and 0.045 °C/year, respectively. Regarding the Tmin data, a significant positive trend was observed in July at a rate of 0.033 °C/year

Assessing spatial soil erosion under climate change using SWAT model in a semi-arid watershed of northeastern Tunisia

This study assesses the impact of climate change on streamflow and soil erosion dynamics in the Wadi Rmel watershed, using the Soil and Water Assessment Tool model under RCP4.5 and RCP8.5 scenarios. The model achieved an NSE of 0.61 and R ^2 of 0.66 during calibration and NSE of 0.83 and R ^2 of 0.85 during validation phase. Climate projections from EURO-CORDEX models were analyzed across three timeframes: short-(2021–2044), medium-(2045–2069), and long-term (2070–2100). Results show decreasing precipitation across all scenarios, with reductions below 10% in the short term and up to 40% in the long term. For the long term, maximum temperature is predicted to increase by 1.5–5.2 °C across all RCP8.5 scenarios. Streamflow is expected to decline from a baseline average of 0.27 m ^3 /s, dropping to 0.21m ^3 /s in the short term, with further reductions over time. The impact of climate change on soil erosion exhibits spatio-temporal variability, with reductions across sub-basins, influenced by factors such as vegetation cover and anthropogenic factors. While erosion rates are projected to decline in most areas, sub-basins with minimal vegetation cover, especially in the southwestern region, remain highly vulnerable. The highest erosion reductions are observed in central and northeastern sub-basins, linked to better vegetation and conservation measures. These findings reveal key gaps in land management and opportunities to strengthen resilience against future water challenges in semi-arid regions

Spatio-temporal analysis of the grombalia aquifer dynamics--northern east of Tunisia

International audienceAquifer maps are key tools for water resources management, and allow to characterize awater table distribution and variability. The Grombalia plain in the northeast part of Tunisia was studied to identify the origin of groundwater recharge and to specify the type of recharge in the whole study area. It aims to investigate the impact of recharge schemes on the piezometric evolution of the water table. Furthermore, the purpose is to investigate the origin and dominant factor of the recharge. The methodology of this work includes two methods of analysis of the dynamics of the piezometric heads of this aquifer, namely the interpretation of piezometric maps for an evaluation of the spatial evolution and the study of piezometric sections. Both methods allow to distinguish between the different types of recharge, show which recharge sources is the most important in supplying the groundwater. In addition, they permit to analyze in detail the piezometric evolution and the impact of the various hydraulic structures on the piezometry. Without forgetting the naturel recharge coming directly from the soil surface and depending on the permeability, there is another natural recharge which comes from flooding areas. In Grombalia groundwater, this natural recharge occurs mainly at Wadi Ejjorf, Wadi Sidi Toumi and Wadi Ejdida sites. This recharge is accented for rainy years and mainly after flooding events. This study shows the picks at all the recharge sites between 1999 and 2009. However, an overexploitation of the aquifer was observed in Soliman-Fondok Jedid, Boucharray, Bou Argoub, which presented local depression zones. The used methodologies are very important tool to choose the best recharge site and allow to adjust the hydrodynamic models. In fact, there is an urgent need for assessing various aspects of ground water resources through a process of systematic data collection, analysis and synthesis

Comparative Analysis of Climate Change Impacts on Climatic Variables and Reference Evapotranspiration in Tunisian Semi-Arid Region

Systematic biases in general circulation models (GCM) and regional climate models (RCM) impede their direct use in climate change impact research. Hence, the bias correction of GCM-RCMs outputs is a primary step in such studies. This study compares the potential of two bias correction methods (the method from the third phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3) and Detrended Quantile Matching (DQM)) applied to the raw outputs of daily data of minimum and maximum air temperatures and precipitation, in the Cap-Bon region, from eight GCM-RCM combinations. The outputs of GCM/RCM combinations were acquired from the European branch of the coordinated regional climate downscaling experiment (EURO-CORDEX) dataset for historical periods and under two representative concentration pathway (RCP4.5 and RCP8.5) scenarios. Furthermore, the best combination of bias correction/GCM-RCM was used to assess the impact of climate change on reference evapotranspiration (ET0). Numerous statistical indicators were considered to evaluate the performance of the bias correction/historical GCM-RCMs compared to the observed data. Trends of the Hargreaves–Samani_ET0 model during the historical and projected periods were determined using the TFPMK method. A comparison of the bias correction methods revealed that, for all the studied model combinations, ISIMIP3 performs better in reducing biases in monthly precipitation. However, for Tmax and Tmin, the biases are greatly removed when the DQM bias correction method is applied. In general, better results were obtained when the HadCCLM model was used. Before applying bias correction, the set of used GCM-RCMs projected reductions in precipitation for most of the months compared to the reference period (1982–2006). However, Tmin and Tmax are expected to increase in all months and for the three studied periods. Hargreaves–Samani ET0 values obtained from the best combination (DQM/ HadCCLM) show that RCP8.5 (2075–2098) will exhibit the highest annual ET0 increase compared to the RCP4.5 scenario and the other periods, with a change rate equal to 11.85% compared to the historical period. Regarding spring and summer seasons, the change rates of ET0 are expected to reach 10.44 and 18.07%, respectively, under RCP8.5 (2075–2098). This study shows that the model can be used to determine long-term trends in ET0 patterns for diverse purposes, such as water resources planning, agricultural crop management and irrigation scheduling in the Cap-Bon region