Since Horton in 1965, many authors have sought to aggregate different variables characterizing the state of water into a single value called Water Quality Index ( $WQI$ ). This index is intended to facilitate the operational management of water resources and their allocation for different uses. Detailed and operational description of the main $WQI$ calculations are here reviewed. The review contains: (1) an historical analysis of the evolution of $WQI$ calculation methods by looking both at the choice of variables, the methods of weighting and aggregating these variables into a final single value; (2) an illustration of the contradictions observed in the final result when, on the same database, the $WQI$ is calculated by different methods; (3) the significant progress possible via fuzzy logic to define a $WQI$ adapted to specific water use.

Semiarid Tunisia is characterized by agricultural production that is delimited by water availability and degraded soil. This situation is exacerbated by human pressure and the negative effects of climate change. To improve the knowledge of long-term (1980 to 2020) drivers for Land Use and Land Cover (LULC) changes, we investigated the semiarid Rihana region in central Tunisia. A new approach involving Google Earth Engine (GEE) was used to map LULC using Landsat imagery and vegetative indices (NDVI, MSAVI, and EVI) by applying a Random Forest (RF) classifier. A Rapid Participatory Systemic Diagnosis (RPSD) was used to consider the relation between LULC changes and their key drivers. The methodology relied on interviews with the local population and experts. Focus groups were conducted with practicians of the Regueb Agricultural Extension Services, followed by semi-structured interviews with 52 households. Results showed the following: (1) the RF classifier in Google Earth Engine had strong performance across diverse Landsat image types resulting in overall classification accuracy of ≥0.96 and a kappa coefficient ≥0.93; (2) rainfed olive land increased four times during the study period while irrigated agriculture increased substantially during the last decade; rangeland and rainfed annual crops decreased by 58 and 88%, respectively, between 1980 and 2021; (3) drivers of LULC changes are predominately local in nature, including topography, local climate, hydrology, strategies of household, effects of the 2010 revolution, associated increasing demand for natural resources, agricultural policy, population growth, high cost of agricultural input, and economic opportunities. To summarize, changes in LULC in Rihana are an adaptive response to these various factors. The findings are important to better understand ways towards sustainable management of natural resources in arid and semiarid regions as well as efficient methods to study these processes.

Climate change is expected to reduce water availability in the Mediterranean region and water management needs to adapt to future conditions. The aims of this study were (1) to develop a participatory approach for identifying and evaluating management options for river basin climate adaptation and (2) to apply and evaluate the approach in four case-study river basins across the Mediterranean. As part of the approach, a diverse group of stakeholders joined a series of workshops and consultations in four river basins located in Cyprus, Slovenia, Spain and Tunisia. In each river basin, stakeholders expressed their views on challenges in their river basins, as well as options to tackle these challenges. We used the information on challenges, as well as the factors contributing to these challenges to develop a fuzzy cognitive map for each basin. These maps were converted into mathematical models and were used to assess the impact of a total of 102 suggested management options for the four river basins. We linked the options and their estimated impacts with a multi-criteria analysis to identify the most preferred options. The approach was positively evaluated by the participating stakeholders and allowed the link of stakeholders’ knowledge and perceptions about their river basin with their preferences for options to adapt the management of their river basins to future conditions.

In recent years, farmers in Beja, an agricultural governorate in northwestern Tunisia, have expressed their willingness to use urban sewage sludge as agricultural fertilizer, especially with the unavailability of chemical fertilizers and the soil type of the region that is poor in organic matter. However, there is an imbalance between the important farmers’ demand versus the limited quantity of sludge produced by the Beja wastewater treatment plants (WWTPs). In the face of this, this study aims to identify the problems related to the agricultural reuse of sludge in Beja and propose solutions to solve them. The quality of the sludge produced by the five Beja WWTPs was assessed based on physicochemical and microbiological parameters. The data were collected using the Delphi method, with 15 experts representing different positions on the issue treated. The SWOT-AHP methodology was used to define the strategies promoting the sustainable use and management of urban sewage sludge for sustainable agricultural development in Beja. Results showed that there were no problems with compliance with the Tunisian standards NT 106.20 for the sludge produced. A set of twelve practical conclusions was identified, constituting the strategies of Strengths–Opportunities, Strengths–Threats, Weaknesses–Opportunities, and Weaknesses–Threats deduced from the SWOT-AHP.

Mixed cropping systems can constitute important agroecological adaptation strategies for enhancing crop growth and productivity in view of climate change, while reducing the need for synthetic fertilizers and providing important ecosystem services. The aim of this study was to investigate growth, competitiveness, and productivity of two forage mixtures combining triticale (X triticosecale Wittmack) to common vetch (Vicia sativa L.), and to fenugreek (Trigonella fœnum-græcum L.) in different mixture combinations (40% T–60% V vs. 60% T–40% V and 40% T–60% F vs. 60% T–40% F). Field results showed that both forage legumes were higher inside the different crop mixtures (+225% for vetch, +94% for fenugreek) than in monocropping. In regard to the competition ration (CR), triticale was the more dominant and competitive species in three out of four studied mixtures. Forage yield was higher in crop mixtures than for corresponding sole crops. Yield gain was greater for common vetch-based mixtures than fenugreek ones (+60% vs. +30%). The results show that using cereal–legume mixtures can provide important productivity increase for fodder yield compared to conventional pure crops. The method is an important adaptive agricultural strategy in view of climate change.

Climate change and land degradation menace ecosystem sustainability. This study assessed the effectiveness of integrating nature-based solutions (NBSs); soil and water conservation techniques, agroforestry, and reforestation, to mitigate these impacts. Focusing on carbon storage and sediment retention at the watershed level (Sidi Barrak), the InVEST model quantified changes from 1990 to 2050 under the Business as Usual (BAU) and management scenarios. The results showed a significant decrease in sediment retention and carbon storage from 19.25 to 15.5 t ha⁻¹year⁻¹ and from 1.72 to 1.61 t ha⁻¹year⁻¹, respectively, between 1990 and 2021. By 2050, BAU scenario projections demonstrate a 28% decrease in sediment retention and a 16% drop in carbon storage under Representative Concentration Pathways (RCP) 4.5. The Management scenarios indicate substantial improvements, with carbon storage increasing by 77% and sediment retention by 87% when all strategies were combined. The economic valuation, performed through the application of the cost–benefit analysis, shows positive net benefit values (NPVs) for the different NBS management scenarios. The combined management scenario, which includes soil and water conservation techniques, agroforestry, and reforestation under the same scenario, presents the highest total NPV with 11.4 M€ (2%, 2050), an average of 130 €/ha (2%, 2050), and an opportunity cost of 1.7 M€ compared to BAU. Such results may orient decision-making by providing solid arguments toward ecosystem resilience and climate change mitigation.