Tunisia
Can Nature-Based Solution be the Panacea to the Looming Crisis of Climate Change Induced Water Scarcity in Tunisia?
Despite Tunisia’s efforts in water management, the per capita water availability remained low at only 395 cubic meters (m³) in 2021, falling below the absolute water scarcity threshold of 500 m³ (FAO, 2021). As of 2019, Tunisia had already been among the highest-ranking countries in terms of water stress, evidenced by the significant proportion of freshwater withdrawal compared to available resources. Ecosystems, particularly forests, play a crucial role in providing freshwater and protecting water reservoirs from siltation. However, these reservoirs face challenges from soil erosion and sediment export, with an average accumulation rate of 22.59 percent in 2021 (MARHP, 2022). The country's susceptibility to droughts and water scarcity is compounded by its semi-arid climate and vulnerability to climate change (NWSR, 2020). Climate changes is expected to further reduce water resources, intensify erosion, and worsen land degradation due to decrease in rainfall, higher temperatures, and greater evapotranspiration rates (Abouabdillah et al., 2014). Furthermore, Tunisia's heavy reliance on groundwater exacerbates these challenges. While government initiatives aimed at tackling these issues are appreciated, innovative solutions will be imperative to ensure the long-term sustainability of water resources in a changing climate in Tunisia.
Assessment of water ecosystem services: InVEST Seasonal Water Yield (SWY)
The SWY Model uses a simplified approach that differentiates between two types of flow: quick flow and baseflow. The baseflow is water that reaches groundwater system during in between rain events or during the dry season and has residence times of months or even years. Base flow depends on precipitation depth, the number of precipitation events in each month and the curve number or runoff (CN). CN is assigned to each land cover class and used to convert rainfall to runoff for these different classes. The model takes several inputs to estimate water yield, including rainfall, digital elevation model, soil types and properties, hydrological data, observed runoff and a land cover map. After calibration, the model simulated climate change scenarios (SSP) and proposes adaptation measures: nature-based solutions such as afforestation, water and soil conservation techniques, and agroforestry. Two levels of intervention were considered “intermediate measures” and “maximum measures” based on the surface area of intervention.
Water availability under climate change and management scenarios
Ground water recharge
In SSP2 climate scenario with no measure (BAU), the groundwater recharge is predicted to decrease by 25%, compared to the baseline. However, with intermediate and maximum measures of land management, the groundwater recharge is predicted to increase by 30% and 52%, respectively compared to BAU scenario. In the SSP3 Scenario horizon 2050, there is an expected considerable decline of 32% in groundwater recharge when no land management measures are employed. However, the implementation of intermediate and maximum land management measures is predicted to yield an increase of 19% and 22%, respectively, in groundwater recharge.
Surface water regulation
In the SSP2 scenario horizon 2050, the water base flow is expected to decrease to 157.7 m3/ha in the BAU scenario, a reduction of 21.8% from the current state. However, with intermediate and maximum land management measures, this flow is expected to increase to 24% and 37%, respectively compared to BAU scenario.
In the SSP3 scenario horizon 2050, the absence of any land management measures is projected to cause a significant decline in base flow to 151.2 m3/ha, which is substantially lower than the current situation. With intermediate and maximum land management measures in place, the base flow is expected to increase by 15.4% and 17.2%, respectively, compared to the BAU scenario.
The observed decrease in water base flow and recharge for SSP2 and SSP3 is likely due to increased temperatures, reduced precipitation, and landscape degradation. This highlights the need for urgent and effective climate change mitigation and adaptation measures to reduce the adverse impacts of climate change on water resources.
In this current study, we have explored Nature-based Solutions (NBS) for intermediate and high-level management, including techniques such as afforestation, water and soil conservation methods, and agroforestry. These approaches are integral in bolstering water availability through diverse mechanisms. They aid in boosting the soil's water retention capacity, thereby reducing surface runoff and promoting the infiltration of water into the ground. Consequently, this process replenishes groundwater reservoirs and sustains streamflow, particularly during arid periods.
Furthermore, NBS contribute significantly to groundwater recharge by facilitating water percolation through the soil, effectively replenishing aquifers. This is of supreme importance in areas heavily reliant on groundwater for both drinking water and agricultural irrigation.
Recommendations
Based on the modeling and assessment of hydrological ecosystem services associated with landscape management in Tunisia, the following recommendations and policy implications, in line with its NDCs, can be emitted:
Identifying and prioritizing degraded areas: we recommend using remote sensing and GIS tools to identify areas with high soil erosion and natural vegetation degradation. These areas can then be prioritized for interventions to restore ecosystem services.
Investment in NBS Implementation: Allocate resources and funding towards the implementation of nature-based solutions such as afforestation, soil conservation techniques, and agroforestry. These practices can significantly enhance water availability while also mitigating the impacts of climate change on water resources.
Integrated Water Resource Management (IWRM): Adopt an integrated approach to water resource management that considers the interconnectedness of surface water and groundwater systems. Implement policies and strategies that promote sustainable use and allocation of water resources while also protecting ecosystems that provide important water-related services.
References
FAO (Food and Agriculture Organization) Aquastat data
Tunisia Ministry of Agriculture, Water Resources and Fisheries. 2022. “Phase 5 Report of the Water 2050 Study.”
Abouabdillah, A., White, M., Arnold, J.F., De Girolamo, A.M., Oueslati, O., Maataoui, A., Lo Porto, A. (2014). Evaluation of soil and water conservation measures in a semiarid river basin in Tunisia using SWAT. Soil Use and Management. https://doi.org/10.1111/sum.12146.
NWSR : National Water Sector Report (2020). The Minister of Agriculture, Water Resources and Fisheries, Office of Planning and Hydraulic Balances
![Water in Tunisia](/content/dam/photos/768x384/2024/apr/Base-flow-BAU-SSP3.png)