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 ( W Q I ). 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 W Q I calculations are here reviewed. The review contains: (1) an historical analysis of the evolution of W Q I 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 W Q I is calculated by different methods; (3) the significant progress possible via fuzzy logic to define a W Q I adapted to specific water use.

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Soil erosion vulnerability and extreme rainfall characteristics over the Mediterranean semi-arid region of Tunisia are crucial input for estimation of siltation rate in artificial reservoirs. A comprehensive high resolution database on erosive rainfall, together with siltation records for 28 small reservoirs, were analysed for this region, the Tunisian Dorsal (the easternmost part of the Atlas Mountains). The general life-span of these reservoirs is only about 14 years. Depending on the soil degradation in the different catchments, the corresponding reservoirs display a wide range of soil erosion rates. The average soil loss was 14.5 t ha-1 year-1but some catchments display values of up to 36.4 t ha-1 year-1. The maximum 15-min duration rainfall intensity was used to determine the spatial distribution of rainfall erosivity. The northwestern parts of the Tunisian Dorsal display the most extreme rainfall erosivity. Spatial erosion patterns are to some extent similar; however, they vary greatly according to their location in the "soil degradation cycle?. This cycle determines the soil particle delivery potential of the catchment. In general, the northwestern parts of the Dorsal display modest soil erosion patterns due to the already severely degraded soil structure. Here, the soil surface is often the original bedrock. However, the greatest soil erosion occurs in the mid-eastern parts of the Dorsal, which represents the "degradation front?. The latter corresponds to the area with highest erosion, which is continuously progressing westward in the Dorsal. The large variation between the erosive rainfall events and the annual soil loss rates was explained by two important factors. The first relates to the soil degradation cycle. The second factor corresponds to the degradation front with the highest soil loss rates. At present this front is located at 300 m altitude and appears to be moving along an 80-km westward path starting from the east coast. A better understanding of the above can be used to better manage soils and soil covers in the Tunisian Dorsal area and, eventually, to decrease the soil erosion and reservoir siltation risk

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.