Water

Water resources in the Mediterranean are scarce. They are limited, unevenly distributed and often mismatching human and environmental needs. Three quarters of the resource are located in the northern Mediterranean while three quarters of the needs are in the south and east. As a consequence, approx. 180 million people in the southern and eastern Mediterranean countries suffer from water scarcity (<1,000 m3 capita-1 yr-1). The main water user is agriculture, in particular on the southern and eastern rim. The percentage of irrigated land of the total cultivated area is 25% for the Mediterranean Basin and is currently increasing, likely with higher rates under even drier climate conditions in the future. Water demand for both tourism and agriculture peak in summer, potentially enhancing tensions and conflicts in the future. Municipal water use is particularly constrained in the south and will likely be exacerbated in the future by demographic and migration phenomena. In parallel, northern countries face additional risks in flood prone areas where population and urban settlements are rapidly increasing. Climate change, in interaction with other drivers (mainly demographic and socio-economic developments), has mainly negative consequences for the water cycle in the Mediterranean Basin, including reduced runoff and groundwater recharge, increased crop water requirements, increased conflicts among users, and increased risk of overexploitation and degradation. These impacts will be much more important for global warming higher than 2°C. Strategies and policies for water management and climate change adaptation are strongly interconnected with all other sectors (e.g., the Water-Energy and Food Nexus). Technical solutions are available for improving water use efficiency and increasing reuse. Seawater desalination is increasingly used as adaptation measure to reduce (potable) water scarcity in arid and semi-arid Mediterranean countries, despite known drawbacks in terms of environmental impacts and energy requirements. Promising solar technologies are under development, potentially reducing emissions and costs. Reuse of wastewater is a solution for agriculture and industrial activities but also recharge of aquifers. Inter-basin transfers may lead to controversies and conflicts. Construction of dams contributes to combat water and energy scarcities, but with trade-offs in terms of social and environmental impacts. Overall, water demand management, which increases water use efficiency and reduces water losses, particularly in urban environments, is crucial for a sustainable development. Maintaining Mediterranean diet or coming back to it on the basis of locally produced food and reducing food wastes may save water but also carbon emissions while having nutritional benefits

Variational data assimilation with the YAO platform for hydrological forecasting

International audienceIn this study data assimilation based on variational assimilation was implemented with the HBV hydrological model using the YAO platform of University Pierre and Marie Curie (France). The principle of the variational assimilation is to consider the model state variables as control variables and optimise them by minimizing a cost function measuring the disagreement between observations and model simulations. The variational assimilation is used for the hydrological forecasting. In this case four state variables of the rainfall–runoff model HBV (those related to soil water content in the water balance tank and to water contents in rooting tanks) are considered as control variables. They were updated through the 4D-VAR procedure using daily discharge incoming information. The Serein basin in France was studied and a high level of forecasting accuracy was obtained with variational assimilation allowing flood anticipation

Sensitivity of discharge projections to potential evapotranspiration estimation in Northern Tunisia

Tunisia has a long history of coping with water scarcity, and the quantification of climate change impacts on runoff is important for future water management. A major requirement for such studies is an estimation of potential evapotranspiration (PET), which is challenging as many regions often lack the observational data needed for physically based PET equations. In this study, different PET estimation approaches were used to study the impact of PET estimation on discharge projections for catchments in Northern Tunisia. Discharge was simulated for five catchments using three rainfall-runoff models (RRMs): HBV, GR4 and IHACRES. A general differential split sample test (GDSST) was used for an RRM robustness evaluation based on subperiods with contrasting climatic conditions for the 1970–2000 period. Three cases with varying PET were considered: (1) daily calculated PET, (2) long-term daily mean PET with the same values for calibration and validation periods (calculated over the calibration period) and (3) long-term daily mean PET varying between calibration and validation periods (calculated over the calibration and validation period separately). Over the historical period, the comparison between cases 1 and 3 showed little impact of reduced PET information on the RRM performance and robustness. The comparison of cases 2 and 3 indicated a limited impact of varying PET between calibration and validation on the RRM results. The impact of varying levels of PET information on hydrological projections was also analysed over two future 30-year periods: mid-term period (2040–2070) and long-term period (2070–2100), with two representative concentration pathway scenarios (RCPs 4.5 and 8.5), by comparing cases 1 and 2. The projected discharge with constant PET (case 2) was generally lower than the projected discharge with variable PET (case 1) but the difference in volume change did not exceed 9% for both the time period and the RCP scenario considered. While PET slightly increased under the different climate change scenarios, actual evapotranspiration (AET) was found to decrease. These opposite trends of PET and AET can be attributed to the projected decrease in precipitation. Overall, our results demonstrate that discharge, in semi-arid regions like Northern Tunisia, is not sensitive to PET estimates since AET is mainly controlled by the availability of soil moisture. This finding is useful for performing studies of climate change impact on hydrological cycles in arid regions, as our study shows that simple PET estimation is a valid approach for such studies

Hydrological impacts of climate change in North African countries

International audienc

Evaluating the robustness of conceptual rainfall-runoff models under climate variability in northern Tunisia

International audienc

Cephalometric diagnosis of obstructive sleep apnea in Tunisian subjects: A case-control study.

Objective: The main objective of this case-control study was to determine the anatomic risk factors responsible for the appearance and severity of Obstructive Sleep Apnea (OSA). Methods: Lateral radiographs of 33 patients with OSA, whose diagnosis was already confirmed by polysomnograpy (PSG), were compared to those of 33 control subjects. Seven anthropometric and 20 cephalometric variables were studied. The statistical analysis was performed using the SPSS version 17 and the significance rate was set at 5%. Results: the findings of our study support the literature data showing that patients with OSA are older and fatter [ BMI: 36,94kg/m² vs 23,21kg/m², p 0.001], and have more craniofacial anomalies manifested by an inferiorly positioned hyoid bone (H_MP: 20.13mm vs 13.48mm ; H_C3: 36.81mm vs 43.10mm ; H_ENA: 99.45mm vs 90.66mm ; p 0.001) and a narrower oropharynx associated with an increase of the tongue and soft palate length p(UH)=0.010 and p(UL)=0.000, p(TgLt)= 0.000).Conclusion: Fatty subjects with craniofacial abnormalities are more predisposed to develop OSA. Key words: obstructive sleep apnea, cephalometry, diagnosis, hyoid bon

Characterization of spectral features of cavity modes in one-dimensional graphene-based photonic crystal structures

In this study, a numerical approach based on the transfer-matrix method (TMM) is employed to investigate, the optical features of an ultra-high-quality factor (Q-factor). The cavity is formed by incorporating a defect layer in a one-dimensional graphene photonic crystal (1D-GPC) structure. The cavity modes are identified, and the dependency of their spectral characteristics on the opto-geometrical parameters of the structure and the chemical potential ($$\mu _{\mathrm{C}})$$ of graphene are investigated in detail. Our simulation results indicate that a tunable ultra-high Q-factor is attainable with the proposed cavity device. It is shown that the eigenfrequencies of the cavity modes vary in similar way versus the considered parameters. While, their Q-factors exhibit some differences in their changes with the thicknesses of the material layers. We have also noticed that the proposed cavity exhibits a cavity mode whose Q-factor increases exponentially with the number of layers in the distributed Bragg reflectors and with the graphene chemical potential. The observed tunable features of such kind of high Q-factor cavity make it an ideal candidate for the realization of ultrasmall tunable narrowband filters, sensing devices, and low-threshold lasers