S21

Hydrological models’ parameters do not transfer well between periods with different climatic conditions; particularly when parameters calibrated on a wetter climate are used to project streamflow during a drier period. Many Mediterranean and semi-arid regions worldwide experienced multi-annual, persistent drought conditions in recent decades, which exposed these limitations of hydrological models and their most common calibration methods. Additionally, projections indicating a likely warmer and drier future in these regions render this issue particularly disquieting, especially as models tend to overestimate water availability during dry periods.

In south-eastern Australia, the Millennium drought (ca. 1997­–2009) called attention to this issue due to its effects on the hydrological behaviour of many catchments. Specifically, models calibrated on pre-drought conditions routinely overestimate streamflow when forced with drought data. However, in operational simulation, it has been theorised that models calibrated on long timeseries that include the Millennium drought will be able to perform well under a future drier climate.

We tested this hypothesis by studying the performance of five conceptual rainfall-runoff models in 155 catchments in the southern Australian state of Victoria. We calibrated the models on different periods, some including the drought and post-drought themselves, and compare the performance across parameter sets during and after the drought. We observe that naively extending calibration sequences to include the drought did not significantly improve model performance across these catchments, neither during the drought itself nor, in most cases, in the decade after the drought. Further adding the post-drought period also provided very limited improvement in this period and is unlikely to make any operational difference, despite drought and post-drought making up at least 30% of the calibration sequence.

These results highlight the importance of the choice of data and method used for calibrating hydrological models under transient climate and suggest that more sophisticated calibration methods are needed in this context. These include calibration with explicit and distinct treatment of different climate regimes (e.g. using multi-objective optimisers). However, where changes in climate triggers drastic shifts in catchment behaviour, novel and more adaptable model structures may be necessary to confidently project streamflow under future climate.

How to cite: Trotter, L., Saft, M., Peel, M., and Fowler, K.: Extending calibration sequences to include multi-year drought is not sufficient to train models for future drier climate, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-96, https://doi.org/10.5194/iahs2022-96, 2022.

The Mediterranean region has experienced accelerated socioeconomic development, primarily due to population expansion. This had a substantial influence on water resource availability, with arid and semiarid areas being the most affected. In Morocco, both surface water and groundwater are already affected by reduced precipitation and massive withdrawals due to the growing demand for irrigated agriculture. The present study is carried out in the piedmont of the High-Atlas Mountains (central Morocco). This agro-hydrosystem is mainly fed by intermittent and ephemeral wadis that cross through the piedmont to the Haouz plain and discharge into the mainstream Tensift wadi. Groundwater is used for drinking purposes and serves as a buffer reserve for irrigation during dry seasons. A comprehensive analysis of hydro-climatological data between 1970 and 2018 is performed together with associated agricultural land use trends over the period 1984-2020. Over 48 years of monitoring, the analyses revealed a substantial decrease of water resources. The standardized precipitation index (SPI) showed three main meteorological drought periods, 1982-1986, 1998-2008 and 2013-2017. A decreasing trend of streamflow by nearly 40% has been noticed. The groundwater level has been decreasing dramatically over the last 2 decades.  Surprisingly, this decrease in water resources was associated to an agricultural transition from seasonal crops (cereals) to perennial crops (olive trees). This conversion is likely to exacerbate the water shortage, leading to an overexploitation of groundwater resources to satisfy the growing agricultural demand.

Keywords: Mediterranean region, precipitation, groundwater, streamflow, LULC, trends.

How to cite: Ouassanouan, Y., Fakir, Y., Simonneaux, V., Kharrou, H., and Chehbouni, A.: Long-term assessment of water resources and agricultural changes across a semiarid Mediterranean piedmont (High-Atlas, Morocco), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-218, https://doi.org/10.5194/iahs2022-218, 2022.

The representation of soil-atmosphere exchanges is fundamental to understand the surface level processes and their interaction with the biosphere. Land surface models (LSM) are continuously improved to better represent these interactions. However, several surface heterogeneity factors such as localized water supply, land covers or various vegetation species make it still challenging to realistically represent the different surface processes. The three dimensional forest model MAESPA and the one dimensional soil-atmosphere-biosphere interaction model ISBA have been applied in order to study the water and energy budgets of the rain-fed olive orchard of Nasrallah in semi-arid area.  Both models have similar approach in terms of soil representation while MAESPA model uses a 3-D individual trees representation and simulation. The aim of this work is to take into account the Nasrallah site heterogeneity factors in order to improve the representation of surface processes. The outcome of this work underlines the contribution of a better consideration of the olive orchard spatial heterogeneity on the surface fluxes simulation. Improvement in water and energy fluxes estimation with more realistic transpiration evaluation have been found compared to field observations with smaller RMSE especially for evapotranspiration by up to 0.2 mm and net radiation flux by up to 7 W/m2.

How to cite: Zied, S.: Impact of canopy scale heterogeneity on modelling the water and energy budget of a rainfed olive orchard, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-100, https://doi.org/10.5194/iahs2022-100, 2022.

Soil moisture content influences the partitioning of net radiation into latent and sensible heat fluxes that, in turn, affect the dynamics of the atmospheric boundary layer depth and concomitant generation of precipitation. The interactive effect between soil moisture and precipitation has been found to be stronger in areas where soil moisture temporal variability is enhanced such as in arid and semiarid regions, and in transitional regions between dry and wet climate. For this reason, variability in soil moisture at multiple time scales continues to draw attention in climate science and hydrology. In this work, the soil moisture variability at multiple scales for a typical Mediterranean ecosystem, has been quantified using the spectrum of soil moisture.

The case study is the Orroli site in Sardinia (Italy), a typical semi-arid Mediterranean ecosystem which is an experimental site for the ALTOS European project of the PRIMA MED program.

The spectrum of root-zone soil moisture content for this Mediterranean ecosystem is analyzed using 14-years of half-hourly measurements. A distinguishing hydro-climatic feature in such ecosystems is that sources (mainly rainfall) and sinks (mainly evapotranspiration) of soil moisture are roughly out of phase with each other. For over 4 decades of time scales and 7 decades of energy, the canonical shape of the measured soil moisture spectrum is shown to be approximately Lorentzian determined by the soil moisture variance and its memory but with two exceptions: the occurrences of a peak at diurnal-to daily time scales and weaker peak at near annual time scales. Model calculations and spectral analysis demonstrate that diurnal and seasonal variations in hydroclimate forcing responsible for variability in evapotranspiration had minor impact on the normalized shape of the soil moisture spectrum. However, their impact was captured by adjustments in the temporal variance. These findings indicate that precipitation and not evapotranspiration variability dominates the multi-scaling properties of soil moisture variability consistent with prior climate model simulations.

How to cite: Corona, R., Montaldo, N., and Katul, G. G.: Multiscale analysis of soil moisture variability for a typical semi-arid Mediterranean ecosystem, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-254, https://doi.org/10.5194/iahs2022-254, 2022.

After having swept over western France, the ALEX storm led to an exceptional Mediterranean rainfall event which hit the “Alpes Maritimes” region during the night of the 2nd to 3rd October 2020. The rainfall accumulations observed on 12 to 24 hours durations were unique in this region, with a record of 663mm in 24h (EDF raingauge, Les Mesces).

Form West to East, several valleys, mainly those of Tinée, Vésubie, and Roya were affected by major floods, landslides, sediment transport and geomorphological changes. The hydrometric network was almost destroyed. The human and material damages were considerable, with many fatalities and missing people, several villages largely destroyed, and important destructions of communication and transport networks.

A lot of technical post-flood surveys were launched by national authorities to gather a detailed knowledge of the event characteristics, with regard to rainfall accumulations, water discharges, description the torrential phenomena, and inventory of damages. This communication is focused on the question of water discharges.

National and local authorities and organisms, universities and companies, were involved in different post-flood surveys aiming at gathering information on the peak discharges and the hydrographs of the floods, for their own needs and/or within structured programs (Administrative survey, HYMEX research project www.hymex.org).

Several kind of discharge field estimations were provided using field survey measurements, satellites images, post-event Lidar data, combined with hydraulic estimations based on hydraulic formulas, and 1D/2D hydraulic models. Several teams also applied hydrological models based on radar quantitative precipitation estimates, to calculate hydrographs at different basins outlets.

To combine and draw a uniform synthesis of all these results, a consensus exchange was launched to share the knowledge gathered by the different data providers. The objective was to compare, assess, and propose common intervals of peak discharges in the different impacted valleys. We also evaluated for each valley the return period of the final interval of discharge established by the consensus.

The final product is an official administrative document, established at the end of October 2021 by the French state authorities, providing the peak discharge values to be used for post flood studies, reconstruction, and prevention measures.

How to cite: Pons, F., Bonnifait, L., Criado, D., Payrastre, O., Billaud, F., Brigode, P., Fouchier, C., Gourbesville, P., Kuss, D., Le Nouveau, N., Martin, O., Nomis, S., Paquet, E., and Cardelli, B.: Towards a hydrological consensus about the 2nd – 3rd October 2020 ALEX storm event in the French “Alpes Maritimes” region, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-383, https://doi.org/10.5194/iahs2022-383, 2022.

Small communities of the semi-arid region suffer not only with water scarcity but also with data scarcity. The lack of data to perform water management at the local level is a common problem faced in developing countries. The absence of monitoring of water levels of small reservoirs across Ceará State (Northeast Brazil) results in inefficiencies in local water management and in difficulties to fully comprehend the extension of the impact of these changes in the natural streamflow and in the water supply for the state’s network of strategic dams. Small reservoirs construction is the individual private strategy mostly performed to cope with the local droughts. Recent studies shows a strong expansion of this strategy in the recent years, with the construction of more than 100.000 small reservoirs just in one of the state basins. This aspect reveals the necessity of strategies to obtain reliable information about these small reservoirs to perform a comprehensive estimation of these reservoirs impacts in both the local and state level of water management. In this study, local drone images were obtained for a small reservoir in the Ceará State. Remote sensing was used to obtain the reservoir depth-area-volume relationship and reverse water balance technique was used to estimate the different water fluxes and assess the local water availability. The results shows the inefficiency of these small reservoirs due to high evaporation losses, reflecting its high vulnerability to droughts. The proposed methodological scheme proves to be powerful in generating hydrological information by the intricate use of data, besides being replicable for other reservoirs in arid and semiarid regions.

How to cite: Estacio, A., Rocha, R., Linhares, S., Vieira, L., Alves, R., and Martins, E.: Estimating water flows and water availability in a poorly monitored semiarid small dam using reverse water balance and remote sensing., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-396, https://doi.org/10.5194/iahs2022-396, 2022.

The alarming climatic and anthropogenic impacts call for urgent adaptation and mitigation measures and water management policies that should be more based on regional research by deepening the knowledge on the spatial and temporal variability of hydrological resources all over the Mediterranean.

A climatic, physiographic, and hydrological homogeneity across the Mediterranean has been detected but not yet confirmed. Mediterranean climate is known for its precipitation seasonality and the alternation of humid winters and dry summers which conditions rivers flow regimes, landcover, agriculture and consequently any water resources management plan. Several physiographic traits could be also observed across the Mediterranean, like the elevated and exposed karstic features, and the cultivated and managed areas. Hydrologically, global river regimes were classified based on monthly average flows only, and Mediterranean regimes were identified under 3 of the 15 global classes with a clear relation to Köppen’s Mediterranean climate.

Thus, we first studied the flow regimes of 55 Mediterranean catchments to verify if Mediterranean rivers fall into same regime class. Second, we characterised the Mediterranean hydrological response through different water balance functional models as advanced by Budyko, L’vovich and elaborated by Ponce & Shetty and Sivapalan. We also defined from the functional model results the total runoff and groundwater runoff gains as the ratio of the runoff coefficients to annual precipitation, a notion advanced by Ponce and Shetty and elaborated as a sensitivity to precipitation and called elasticity by Harman. The analysis of the runoff gains and elasticity across the Mediterranean and through the climatic and physiographic classes characterised furthermore the hydrological behaviour similarity and variability, and the competition between the water balance components of the Mediterranean catchments.

The water balance analysis highlighted the Mediterranean trend following the general climatic setting from the wet Northern region to the arid Southern region; it also showed hydrological homogeneity for mountainous karstic and snow influenced catchments which yield the highest baseflows and runoff coefficients, especially those located in moderate climate region. However, they are the least sensitive to the humidity index P/Ep which make their hydrological behaviour very interesting to study under RCP 4.5 or RCP 8.5 climate change scenarios.

How to cite: Allam, A., Moussa, R., Najem, W., and Bocquillon, C.: Hydrological Characterisation of Mediterranean Catchments, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-699, https://doi.org/10.5194/iahs2022-699, 2022.

Dehesas are a characteristic Mediterranean mountain ecosystem, result of a co-evolution of autochthonous ecosystems and human settlement in a sustainable balance, with high relevance from both the environmental (biodiversity) and socioeconomic (livestock farming, including Iberian pork food industry) point of views. They are characterized by a complex vegetation cover structure composed of isolated trees, mainly holm oak, cork oak and oak, Mediterranean shrubs, and pastures. This complex vegetation organization is the main determinant of the water and energy balance partitioning and therefore of the hydrological states of the ecosystem. The methodologies traditionally used to assess the hydrological role of vegetation usually are not able to correctly represent this complexity. On the one hand, distributed physically based hydrological models usually lack a detailed vegetation representation at subgrid scale. On the other hand, the spatiotemporal resolutions of traditionally used satellite remote sensing information are not enough to capture these vegetation dynamics.

This work proposes to improve the vegetation representation over this complex ecosystem combining remote sensing information at different spatiotemporal scales. A dynamical spectral mixture analysis using Sentinel-2 data is developed in the Cardeña-Montoro Natural Park (southern Spain). Terrestrial photography taken hourly at two spatial scales, detail (∼m) and plot (∼100m) at an experimental site located within the area, are used as ground truth. Detail scale images allowed to monitor vegetation changes throughout the year (e.g. tree blooming, pasture wither) and are used to select different combinations of endmembers to include in the analysis. Images at the plot scale are used to validate the obtained vegetation dynamical product. The new product, with errors smaller than 5% during the validation process, not only constitutes a better representation of vegetation, but is also the first step in a data assimilation scheme for better hydrological processes representation over these areas.

This work has been funded by project SIERRA Seguimiento hIdrológico de la vEgetación en montaña mediteRránea mediante fusión de sensores Remotos en Andalucía, with the economic collaboration of the European Funding for Rural Development (FEDER) and the Office for Economy, Knowledge, Enterprises and University of the Andalusian Regional Government.

How to cite: Pimentel, R., Torralbo, P., Aparicio, J., Andreu, A., González-Dugo, M. P., and Polo, M. J.: Improving the hydrological role of vegetation over Mediterranean mountain areas: the study case of the dehesa ecosystem in Cardeña-Montoro Natural Park (Spain), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-677, https://doi.org/10.5194/iahs2022-677, 2022.

The objective of the OPAL (ref: PID2019-110311RB-C22) project is to identify and assess the major pathways delivering nutrients, trace metals and pollutants originated from anthropogenic activities to coastal Mediterranean lagoons connected to intensively used aquifers and their consequences on the lagoon geochemical cycles. One of its goals is “To assess of the role of storms and episodic events in the input of nutrients, metals and pollutants”. Within this framework, the capability of the hydrodynamic model Regional Ocean Model System (ROMS) to simulate fast increase of the Mar Menor coastal lagoon sea level due to extreme flood was tested. In September 2019 the stronger storm and flood registered in the Spanish Levantine area in 87 years occurred. In only 13 hours the sea level of the Mar Menor hypersaline lagoon of 135 Km2 increased 0.6 meters, thus creating a strong halocline due to the fresh water that entered from the floods. The sea level took near 7 days to restore. The morphology of the three outlets communicating the lagoon with the Mediterranean Sea determined their water flux going out the lagoon.

This kind of extreme events produces significant enhancements of the inputs of nutrients, metals and pollutants to the lagoon water column coming from an intensive agriculture watershed. To understand the hydrodynamics behind this phenomenon, the ROMS model was used to simulate this episode. Simulations were validated against sea level, salinity and temperature recorded in the water and included surface water inflow from the land, wet/dry areas, bidirectional nesting, water exchange with the Mediterranean Sea and air/water interaction. The result obtained show the robustness of ROMS simulating this kind of events with two layer halocline system formed due to the fresh water inflow from land in a hypersaline water mass.

How to cite: López Castejón, F., Gilabert Cervera, J., Alcaraz Oliver, N., Tudela Meroño, D., and Rodriguez de Mesas, C.: Modelling of a strong flood event on the Mar Menor coastal lagoon with ROMS, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-581, https://doi.org/10.5194/iahs2022-581, 2022.

The French Riviera, located in the eastern part of the French Mediterranean coast, has experienced devastating flash floods during the last 10 years. Several of these floods were generated by local and very intense rainfall events, leading to significant material and human losses, especially on small coastal catchments, which often have sparse rain gauge networks and are mostly ungauged in terms of streamflow. For example, the October 2015 event affected the Riou de l’Argentière, Frayère and Brague coastal catchments (respectively 47 km², 21 km² and 72 km² to the sea) with intense rainfall (up to 200 mm in only two hours) characterized by a significant spatial variability (up to two times more precipitation on the downstream part of the catchments). In this context, the estimation of catchment rainfall statistics needs to be performed using datasets with high space and time resolutions. The COMEPHORE dataset is a rainfall observational dataset with hourly and kilometric resolution over the entire French metropolitan territory. It is produced by Météo-France, merging both raingauge and radar observations and currently available from 1997 to 2020.

The objective of this study is to explore the COMEPHORE dataset to estimate and gain knowledge on heavy rainfall characteristics over French Riviera coastal catchments. The work focuses on 45 coastal catchments draining more than 10 km² and less 1000 km². Various spatial and temporal descriptors are calculated to describe the intensity and the temporal and spatial dynamics of the precipitation over this Mediterranean region. The temporal evolution of the descriptors is evaluated over the 23 years of available data. Additionally, a focus is made on significant rainfall events observed during the last decades, in order to discuss their frequency, associated weather patterns and their (dis)similarity at the regional scale. Finally, we discuss how the proposed description of the spatial and temporal characteristics of heavy rainfall events affecting the French Riviera can be useful to improve rainfall forecasting, as well as to forecast the associated hydrological responses of the coastal catchments at very short lead times and, ultimately, how it can contribute to reduce losses generated by flash floods.

How to cite: Vigoureux, S., Brigode, P., Poggio, J., Nomis, S., Dreyfus, R., Delestre, O., Ramos, M.-H., Moreau, E., Laroche, C., and Tric, E.: Spatio-temporal characteristics of heavy precipitation observed over the last 20 years on French Riviera coastal catchments, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-476, https://doi.org/10.5194/iahs2022-476, 2022.

Medjerda is a key transboundary watershed (Algeria and Tunisia) in the Maghreb region.  The analysis of rainfall regime in this basin is of paramount importance for water resources management and for regional economic development notably in relation with agriculture. This study examines the rainfall trends over the Medjerda watershed on a multi-temporal scale (monthly, seasonally and annually), taking also the spatial scale into consideration. A database of monthly rainfall observed in 60 stations evenly spread over the watershed is used for this purpose. After filling gaps and homogenisation of data, the Mann-Kendall (MK) test for trend detection was applied to rainfall time series. Prior to the trend detection, a Trend-Free Pre-Whitening (TFPW) procedure has been applied to ensure the independence of the data. Moreover, the Sen’s slope method was adopted to estimate the magnitude of rainfall trends over the catchment. Rainfall values in the different stations were then used to generate a map of interpolated Sen’s slope in order to explore the spatial distribution of rainfall trend within the watershed. The results showed that there is a decreasing trend in annual rainfall over the whole basin, yet non statistically significant. Nevertheless, at smaller scales, there is more rainfall trends detected (increasing or decreasing) for different seasons or months, showing the importance of analyzing also monthly or seasonal trends that may differ from annual trends and have some important consequences in terms of water management . Finally, the influence of different teleconnection patterns (the North Atlantic Oscillation, NAOi, the South Oscillation, SOIi and the Mediterranean Oscillation, MOi) on rainfall trend were also investigated. The analysis showed weak correlations at the seasonal scale. Indeed, NAOi and MOi have a similar effect on winter rainfall demonstrated by a positive correlation, while SOi is negatively correlated with spring rainfall. These results highlight the potential small-scale impacts of large-scale climate oscillations on rainfall trends.

How to cite: Boulmaiz, T., Boutaghane, H., Abida, H., Saber, M., Kantoush, S. A., and Tramblay, Y.: Analysis of rainfall trend and the impact of teleconnection patterns on its variability: case of Medjerda Transboundary Watershed, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-513, https://doi.org/10.5194/iahs2022-513, 2022.

Over the past century, climate change altered precipitation and temperature regimes worldwide.  Recently, Montaldo and Sarigu (2017) showed that Sardinia runoff decreased over the 1975-2010 period, with mean annual values 40% lower than the 1922-1974 period.

These trends may have dramatic consequences on basin water resources, impacting forest sustainability. Forests are frequently exposed to periods characterized by a reduced water availability and increasing temperature that influence the evapotranspiration process (ET),and may increase tree mortality and change tree spatial distribution and density.

The Marganai forest, located in the South-West of Sardinia (Italy), is a Long-Term Ecosystem Research (LTER) Italian site and a European Site of Community Importance (Natura 2000) managed by the Sardinian forest authority (FORESTAS). Trees are mainly Quercus Ilex and historical data are available from 1924, with rain from 16 stations, and runoff one the at the Fluminimaggiore basin section (area of 83 km²). A persistent decrease trend of winter precipitation (Mann-Kendall t of -0.14) impacted runoff (t of -0.26). A distributed hydrological model at basin scale has been developed, which computed runoff, ET and predicted grass and tree leaf area index (LAI). The model has been successfully calibrated for runoff and ET estimation for the 1925–2020 period, confirming a dangerous trend in soil moisture and water availability for the trees.

The hydrologic water balance of the basin were also investigated under future IPCC climate change scenarios. From the General Circulation Models of Flato et al. (2013), we selected the HadGEM2-AO that simulates reasonable approximation of observed past seasonal precipitation and air temperature changes in Sardinia. Using the distributed eco-hydrologic model and future climate scenario we predicted both hydrologic water balance terms (soil moisture, runoff, ET).

The future scenario predicted a reduction of annual precipitation, an increase of rain intensity and extreme events, and an increase of temperature and VPD.

The model predicted a significant decrease of tree LAI (t of -0.79) and runoff (t of -0.11), mainly due to VPD increase. Future scenario predicting further dry will require new strategies in both forestal and water resources planning and management. 

How to cite: Sirigu, S., Corona, R., Montaldo, N., Airi, M., and Mallocci, M.: A semi-distributed eco-hydrological model for the estimation of the effect of the climate change on a Mediterranean forest, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-436, https://doi.org/10.5194/iahs2022-436, 2022.

The deterioration of the environment and more specifically the aquatic medium has nowadays become progressively an issue of great concern worldwide. In the current context of climate change and demographic / economic growth, Algeria is subjected to an increasing stress on water. Due to its relative poorness in surface water harvesting capabilities, the relatively easier exploitation of aquifers became the preferred source for water allocation both to population and to agriculture/industry in Algeria. Mitidja plain that is located south of the capital city Algiers, is the country’s most expanded sublittoral Mediterranean plain.It occurs in the central-north of Algeria, it is oriented East-West and extends over a length of 80 km and a width of 10-20 km. It comprises aquifers that are the main source of drinking water for the whole north-central part of the country. The intensification of industrial and agricultural activities combined with demographic growth and urbanization of the plain, resulted in a clear increase in demand for water accompanied by significant problems of degradation of the groundwater quality. The major ion hydrochemistry and environmental isotope composition (¹⁸O, ²H,³H) of Mitidja alluvial groundwaters were investigated to identify the sources and the processes that affect groundwater composition, water origin, and timing of recharge.

The interpretation of the hydro-geochemical data suggests that groundwater composition is largely controlled by the water-rock interactions, particularly the dissolution of evaporate minerals (Halite,Gypsum/Anhydrite) and ion exchange processes. Elevated content of nitrates indicates that agricultural activities are probably the most significant anthropogenic sources of nitrogen contamination.

The concentrations of Fe, Mn, Pb, and Cd in most samples were found higher than the prescribed limits defined by the World Health Organization (WHO). The application of the Principal Component Analysis (PCA) for trace metals identified two sources of pollution- natural and anthropogenic sources. Information inferred from Oxygen-18 and deuterium ratios reflected the existence of recharge through non-evaporated modern rainfall mostly originating from Mediterranean air masses. Measurable tritium concentrations in groundwaters allowed qualitative identification of the present-day component. It is confirmed thus that this component of the alluvial aquifer is supplied by recent rainfall taking place during the rainy season.

How to cite: Dalale, K., Adnane. s, M., Hamid, A. A., Hadjer, C., Mohamed El .H, C., Messaouda, B., Sid-Ali, O., and Mounia, B.: Geochemical and isotopic study of groundwaters in the Mitidja coastal plain, north‑central Algeria, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-110, https://doi.org/10.5194/iahs2022-110, 2022.

         Even in regions with very sparse population, hydrological processes are rapidly changing in semi-arid areas under the double constraint of climate change and anthropization. This is visible in the Trarza aquifer in south-western Mauritania where we investigated changes in groundwater recharge at different scales of time and space. This flat region of about 40,000 km² is mainly made of a succession of Quaternary sandy dunes and interdune depressions where rainfall varies between 100 and 250 mm.a^-1 from north to south. The apparent data scarcity, because of a very low demographic density and a limited hydraulic infrastructure, forced to search for all sources of hydrodynamic information, recent hydrogeological surveys as well as much older field campaigns. Out of this time scale of 60 years, the geochemical information shows the importance of Holocene eustatic variations in the present groundwater mineralization.

            While rainfall has varied a lot in the last decades (e.g. the dramatic droughts of the 1970s and 1980s), its infiltration in interdune depressions did not vary significantly as suggested by the piezometric stability over the last 50 years. This component of the groundwater recharge is estimated at about 4 mm.a^-1.

            Since 1989, the big Diama dam has raised the mean level of the Senegal River, which is now always higher than the neighbouring groundwater. The additional inflow from the river to the alluvium and to the Trarza aquifer is estimated at about 34 hm³.a^-1. Groundwater recharge from the river and rainfall infiltration over the whole area have the same order of magnitude. An even more recent form of anthropization is the new supply of water to the capital (45 hm³.a^-1), pumped from the Senegal River. The increased injection of urban waste waters in the aquifer has led to a groundwater rise in the Nouakchott area, where several urban districts are now submerged.

            The Trarza aquifer appears then as to be presently much more influenced by human pressures than by climatic fluctuations, but the long term rise of sea level may have heavy consequences before the end of the 21^th century in this very flat region.

How to cite: Mohamed, A. S., Leduc, C., Yeslem, S., Tagarinska, G., and Salek, A.: Impacts of climate variations and human influences on groundwater recharge in the semi-arid Trarza aquifer (SW Mauritania), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-169, https://doi.org/10.5194/iahs2022-169, 2022.

This work assesses the current situation of water resources in Lebanon in term of quantity and quality. Hence, 160 water resources studies were gathered from the literature and divided to three categories: water balance (44%), quality (42%) and management (14%). Each category was further divided into sub-topics. The analysis consists of qualitative analysis that discuss the studies topics and their temporal and geographical extent. And a quantitative analysis that compare results of different articles in each topic. Results show that the majority of studies are recent with 60% of the studies published after 2010. Moreover, disparities exist in the studies spatial distribution with only 25% covering the whole country while another 25% concentrated in the inland agricultural Beqaa plain. Moreover, the emphasis is greater on groundwater than surface water for quantity and quality. In term of precipitation, all studies agree on the high spatial variability but still there are difficulties estimating rainfall especially in mountainous and remote areas. Similarly, snow contribution is still poorly estimated and only available for small areas in Mount Lebanon were ground measurement stations exist. In addition, climatic trends show a tendency towards drier conditions, a shrinking snow cover, and an increase of extreme rainfall events frequency. Moreover, although surface hydrology studies are rare, the available ones show some regional pattern which is promising for prediction in ungauged locations. However, global change impact is poorly represented and the studies that exist point towards a decrease in river and spring discharges. On the other hand, groundwater studies show the prevalence of karstic aquifers with some characterized by a high storage capacity making them a pivotal source of water but also a vulnerable one due to their high infiltration rate. For water quality, the dominant hydro-chemical facies is Ca-Mg-HCO₃ due to the prevalence of carbonate rocks. Moreover, the studies show a degradation in surface and groundwater quality. Salt water intrusion, nitrate and pesticides pollution are main challenges in coastal aquifer and agricultural areas respectively. Finally, the steady increase in water resources studies in Lebanon is, unfortunately, accompanied by a decrease in water quantity and a quality degradation.

How to cite: Merheb, M., Abdallah, C., Moussa, R., and Halwani, J.: Water resources in Lebanon: an overview, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-173, https://doi.org/10.5194/iahs2022-173, 2022.

In crystalline aquifers, groundwater resources are generally scarce and may be subject to salinization, notably in semi-arid areas. In semi-arid Northeastern Brazil (NEB), the processes at the origin of the high and heterogeneous salinity observed in the crystalline basement are still controversial. This field study demonstrates how the use of stable and radioactive isotopes and dissolved gases, combined with hydrodynamic and hydrochemical methods, are powerful tools to understand the hydrogeological functioning and the salinization processes of fractured aquifers in such a region.

The study area is located in the state of Ceará (NEB). Monthly and hourly piezometric data were collected respectively from March 2018 to December 2019 over a network of 56 boreholes, and from November 2016 to December 2019 in four of these boreholes. Chemical sampling (major ions and/or minor and trace elements) was carried out in 27 boreholes in December 2017, in 38 in June 2018 and 20 in June 2019. Stable (¹⁸O, ²H) and radioactive (¹⁴C, ³H) isotopes, as well as CFC and SF₆ concentrations were also measured on a total of 137, 10 and 10 samples, respectively.

The strong heterogeneity of the crystalline aquifer was highlighted by Electrical Conductivity (EC) ranging between 1000 and 15000 μS/cm and contrasted temporal variations of EC or piezometric levels. Stable isotope data showed that groundwater recharge occurs through both direct and indirect infiltration of evaporated surface (45-65% on average for the latter). Multi-tracer dating confirms that groundwater is relatively recent (from decades to hundreds of years, with a large contribution of post-1950 water) and that circulation processes are fast. The chemical study suggests that the groundwater, originally bicarbonated, becomes progressively enriched in chloride and sodium, due to the strong evapotranspiration in the quite endorheic context. The NaCl salinity is interpreted as originating from rainfall. However, water and chloride budgets modeling shows that the highest salinities can only be explained by direct withdrawal of groundwater by the vegetation roots of the native bush, with an evapotranspiration rate equivalent to the annual recharge.

How to cite: Kreis, M., Taupin, J. D., Patris, N., Lachassagne, P., Vergnaud-Ayraud, V., Burte, J., Leduc, C., and Martins, E.: Use of a multi-tracer approach for the hydrogeochemical characterization of fractured crystalline aquifers in semi-arid region, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-179, https://doi.org/10.5194/iahs2022-179, 2022.

The determination of the origin of salinity in the superficial aquifer of Mornag (NE Tunisia), and the understanding of its hydrological and geochemical behaviours related to severe natural and anthropogenic constraints, were approached by the combined study of chemical elements and stable isotopes (²H and ¹⁸O). This study indicates that: (1) the high salinities of the superficial aquifer of Mornag are mainly explained by the dissolution/precipitation processes of evaporite minerals in the aquifer formation, (2) the present-day recharge during rainwater infiltration brings downward a high content of nitrates and other dissolved salts, (3) infiltration of untreated sewage from the main urban areas contaminates the aquifer, (4) two other sources of dissolved salts in groundwater exist, favoured by the intensive exploitation of the phreatic aquifer. The first one is due to mineralised water infiltration from Meliane Wadi where activities, mainly a cement factory, discharge their wastewater. Intrusion of marine saltwater is the second source of salinity caused by aquifer over-exploitation. This hypothesis is supported by the high chloride concentration (>240 meq/l), Br/Cl ratios (>1.8 ‰) and the piezometric level lower than sea level. On the other hand, the artificial recharge with low mineralization waters by the Mejerda-Cap Bon Canal and the natural recharge in the valley of wadi El Hma, contribute to a dilution of groundwater. The freshwater/saltwater mixing causes geochemical interactions modifying the water chemistry: cationic exchange, precipitation phenomena. Isotopic tools (²H and ¹⁸O) show that the water of this aquifer system is recharging by direct infiltration from the boundary and in the valley of wadis.

How to cite: Ben Alaya, M., Taupin, J. D., Masadek, H., Ayari, I., Patris, N., Chabenne, N., Toumi, B., and Melki, F.: Application of Geochemical and Isotopic Tools to Investigate Water Recharge and Salinization in a Coastal Phreatic Aquifer Suffering Severe Natural and Anthropogenic Constraints: Case of the Mornag Aquifer, NE Tunisia, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-266, https://doi.org/10.5194/iahs2022-266, 2022.

The Mediterranean region is characterised by growing anthropogenic and climate pressures, resulting in increased water demand. Even though groundwater represents a strategic freshwater reserve in the Mediterranean, its status is becoming increasingly uncertain. The uneven distribution of data availability and scant data-sharing policies and systematic monitoring are significant constraints for management and vulnerability assessments. The objectives of this work are: i) characterization of significant changes in groundwater level time series in the region, ii) comparison of groundwater level models with in-situ data, iii) determine the influence of drivers in the temporal changes as well as the spatial distribution of groundwater levels. 

A database has been developed with over 8,000 time series of groundwater levels collected from national monitoring systems of Spain, Portugal and France, concentrating most measurements after 1980. At first, a search for long term trends and temporal patterns is performed on the most complete time series in the 1985-2014 period. Correlations between significant trends and environmental and anthropogenic drivers are assessed. Furthermore, the outputs of three steady-state global groundwater models (Reinecke et al. (2019), de Graaf et al. (2015) and Fan et al. (2013)) are compared to both interpolated grid-based and piezometer observations. And the relationship between the spatial distribution of groundwater level with explanatory variables is characterized.

Significant groundwater level changes can be found in at least one third of the assessed piezometers. The simulated steady-state hydraulic head obtained from the three models showed a good agreement with the in-situ data in the Iberian Peninsula. A combined analysis of the temporal and spatial drivers for groundwater dynamics at a regional scale will ameliorate groundwater process understanding in the Mediterranean region. This study also makes a case about the importance of consistent and reliable monitoring as a necessary step for management of the resource. 

Acknowledgement: This work was supported by Sustain-COAST and InTheMED projects. Sustain-COAST - funded by the German Federal Ministry of Education and Research (Grant 01DH19015) under the EU PRIMA 2018 programme. InTheMED - funed by the PRIMA 2019 programme supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 1923.

How to cite: Chavez Garcia Silva, R., Ben-Salem, N., Reinecke, R., Rode, M., and Jomaa, S.: Understanding groundwater drivers in the Mediterranean region using a combination of modeling and in-situ data at a regional scale, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-344, https://doi.org/10.5194/iahs2022-344, 2022.

The Mediterranean region is experiencing rapid population growth, increasing water demand, and faster climate warming. Groundwater plays a central role in the development of the Mediterranean by ensuring food security, buffering climate changes impacts and maintaining socio-economic stability and ecosystems integrity. However, despite groundwater being recognised as a powerful catalyser against climate- and human-induced effects, its status remains unknown, and its budget is uncertain. Moreover, the lack of appropriate groundwater monitoring programs at a regional scale, data sharing policy, and fragmented water policy and governance have complicated this vital resource's sustainable utilisation and protection.

To this end, an international and multidisciplinary team of scientists with complementary skills have joined efforts through two PRIMA-funded projects (Sustain-COAST and InTheMED) towards better groundwater management and governance in the Mediterranean. In this respect, the Sustain-COAST Living Labs provide the setting to explore innovative governance approaches that could be scaled to increase resilience and adaptation capacity across the Mediterranean. At a regional scale, efforts target detailed water policy examination, pathways exploration towards the reinforcement of in-situ data collection, and groundwater modelling. Examination of water policy of the Mediterranean revealed an unbalanced situation between South Europe, characterised by complete, harmonised and straightforward water policy. Conversely, in North Africa and Middle East, water policy was found complex, not regionalised and fragmented in various initiatives. Results also showed the Mediterranean has become increasingly dependent on cereal importation over local food production, which poses a severe threat to its best diet overall and food security. Results suggested that combining in-situ data and regional groundwater modelling can offer further insights into this data-scarce region. Believing “that no one size fits all”, lessons learned from success stories, and tailored solutions to typical demonstration sites from both shores of the Mediterranean region are of extreme importance.

Acknowledgement: This work was supported by Sustain-COAST and InTheMED projects. Sustain-COAST was funded by the German Federal Ministry of Education and Research (BMBF, Germany, Grant 01DH19015) under the EU PRIMA 2018 programme. InTheMED is part of the PRIMA 2019 programme supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 1923.

How to cite: Jomaa, S., Ben-Salem, N., Chávez, R., Reinecke, R., Varouchakis, E., Vasco Silva, J., Ceseracciu, C., Phuoc Lai Nguyen, T., Daloglu Cetinkaya, I., K. Saysel, A., K. Copty, N., Rouhani, A., Oueslati, M., Mino, E., P. Karatzas, G., Roggero, P. P., Rode, M., and Gómez-Hernández, J. J.: Inclusive and resilient groundwater assessment towards sustainable development in the Mediterranean region, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-419, https://doi.org/10.5194/iahs2022-419, 2022.

Semi-arid areas are usually associated with decreasing water levels due to groundwater overexploitation, that threatens the sustainability of the water resource and causes negative environmental impacts. More surprisingly, semi-arid areas also host situations of long-term rising groundwater levels, due to anthropization. Changes in land use and land cover, surface application of groundwater pumped from deeper aquifers, inflow of external resources or insufficient sanitation may generate a significant rise in groundwater levels. Consequences on the local water balance may be not less dramatic than those of overexploitation, as rising groundwater tables compromise i) medium term agriculture, via waterlogging and salinization of soils, ii) urban development, via the saturation of drainage systems and water networks and iii) the environment, via the increase in groundwater discharges towards low-topography areas or surface water masses. Qualitative consequences include the death of crops by hypoxia, the increase of water diseases, or the eutrophication of surface water masses. Illustrated by lessons learnt from Mauritania, Niger, Algeria, Australia and Spain, this paper proposes a typology of contexts and associated consequences. It also illustrates implemented or proposed remediation actions, acting from the causes (land-use restrictions, implementation of drip irrigation, enhancement of sewage networks) to the effects (green belt around cities, drainage of agricultural plots for downstream or more remote rejection, groundwater abstraction at regional scale for further treatment). In a wider scale, this paper highlights a less visible but crucial aspect of the need to anticipate anthropogenic and climatic impacts on groundwater evolution at several timescales

How to cite: Baudron, P., Leduc, C., Mohamed, A. S., Zeddouri, A., Hadj-Said, S., Leblanc, M., Lachaal, F., Tweed, S., and García Aróstegui, J. L.: A not-so-paradoxical groundwater rise in semi-arid environments, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-486, https://doi.org/10.5194/iahs2022-486, 2022.

            Social, economic and environmental changes are deeply affecting the entire Earth. Population growth and agricultural intensification are ever more demanding in natural resources, and especially water that is now threatened in both quality and quantity. This degradation is particularly visible in semi-arid and arid areas. The Sahara desert is typical of these multiple constraints and rapid changes where the sustainable management of water resources is a major issue. In Southern Algeria (P < 80 mm.a^-1, PET > 2000 mm.a^-1), perennial water reserves are groundwater with a small to very small recharge: the biggest regional aquifers are considered as having nearly fossil water. In contrast, the alluvial areas associated with the currently active wadis represent small aquifers which are renewed by a few floods each year. In the case of Wadi Tamanrasset, the alluvial aquifer has an average thickness of 20 m and is exploited by the inhabitants because of its accessibility and its good chemical quality. Rare recharging flood events occur mainly between July and September.

            We studied the physical conditions commanding flow and recharge of groundwater, and especially the transfer from surface to groundwater by combining hydrodynamics and isotope tracing of water (¹⁸O, ²H). Monthly monitoring of groundwater level was carried out in around thirty wells and was complemented by automatic recorders with hourly time steps installed since March 2016 in three wells, along a 600 m transect perpendicular to the wadi bed. The part of flood water recharging the alluvial aquifer could then be estimated. The response of the water table is slow and continuous, and becomes visible only two months after the first flood; its maximum rise was 1 m in 2016. Isotopic analyses of rain water on a daily time scale, of the wadi water on a 1-hour time scale during runoff and of groundwater (two complete campaigns in the dry and wet seasons and a specific monitoring of the transect every month) have provided additional information on surface-groundwater transfer.

How to cite: Hadj Saïd, S., Zeddouri, A., Taupin, J. D., Patris, N., and Leduc, C.: Recharge and groundwater dynamics in the Tamanrasset alluvial aquifer (Algerian Sahara), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-491, https://doi.org/10.5194/iahs2022-491, 2022.

The Brazilian semi-arid region presents fragility in terms of surface and groundwater resources due to the irregularity in precipitation regimes and the high evaporation rates. In this context, the communities and the stakeholders are conditioned to seek strategies to cope with droughts, and groundwater emerges as  an alternative supply. This demand requires detailed studies to understand fissural aquifers, given the circulation and storage of water in these aquifers is subject to the presence of structural discontinuities, in particular, influencing the variation of hydrodynamic characteristics and the salinity of wells. The area object of this study corresponds to the Forquilha and Vista Alegre Catchments, in the Ceará State, Northeast Brazil. The present research performed the identification and automatic extraction of the structural lineaments through remote sensing. PALSAR MDE images with 12.5 m spatial resolution and technical data from wells drilled in the region were used. This method promoted the identification of areas of interest for groundwater prospecting. The basins present intermittent drainages and low hydrogeological vocation. Lineaments with preferential NE-SW striking and WNW-ESE striking, in a secondary way, were identified, mainly associated with the drainages of the region. In Vista Alegre the relationship between flow rates and lineaments show a direct affinity. The wells reveal higher flow rates in the western region of the basin, where there is a zone of greater intersection of lineaments, moderate salinity and low variation of the static level in the rainy season. Preliminary results indicate poor interaction between surface and groundwater dynamics. At Forquilha, the relationship between structural features and the most productive wells occurs between structural intersections and drainage. Salinity and static level variation present direct interference in the rainy season, which is reflected in the reduction of the electrical conductivity. In this case, the interaction between the structures and the drainages is more coherent with respect to the lineaments, drainage direction and local relief. Therefore, knowing the structural context of a basin is a necessary increment for a more efficient and planned exploitation of groundwater resources, especially in semi-arid regions that are highly vulnerable to climate change.

How to cite: Linhares, S., Alves, R., Kreis, M., Rocha, R., Estácio, A., Bezerra, J., Martins, E., and Barbosa, N.: Analysis of structural lineaments in the fissural aquifers of the Forquilha and Vista Alegre catchments using remote sensing, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-607, https://doi.org/10.5194/iahs2022-607, 2022.

Mediterranean temporary ponds are very shallow ponds, isolated from permanent water bodies, which undergo a periodic cycle of flooding and drought, and have a characteristic flora and fauna adapted to this alternation. They are identified as one of the worldwide biodiversity hotspots and constitutes therefore a priority habitats according to the Natura 2000 network of the European Union. Despite this protective conservation status, this habitat has suffered continuous degradation and loss, disappearing at a fast rate due anthropogenic impacts and climate pressures. In most cases, temporary wetland disappearance is unintentional and related to a lack of understanding of its hydrological functioning within the watershed.

In this study, we use observations of hydraulic heads, geochemical and isotopic composition of pond and groundwater from the Musella pilote study site (Corsica, Western Mediterranean) to assess the applicability of the isotope hydrology tools for understanding the hydrological behaviour of temporary wetlands and refine their optimal environmental conditions.

By combining together physical and isotope measurements, we demonstrated (i) the main role played by groundwater and subsurface water in the flooding phase of the temporary pond; (ii) the involvement of different water reservoirs in varying proportions over time to maintain the pond filled with water: precipitation, subsurface and groundwater by using d-excess; (iii) the main role played by evaporation in the starting of the drying up phase; and (iv) the connection existing between a geographically isolated wetland and the regional groundwater body.

Results bring the urgent need to consider both surface and groundwater fluxes in wetland’s specific protection statutes. To this aim, we encourage the use of the water stable isotopes to insight the hydrological behaviour of the wetlands in order to have additional cost-effective arbitration elements able to help ensuring their sustainability considering the future consequences of climate change in the Mediterranean region.

How to cite: Mattei, A., Huneau, F., Garel, E., Sorba, L., Santoni, S., and Orsini, S.: Isotope hydrology to insight the behaviour of Mediterranean Temporary Ponds: Implications on sustainable ecohydrological management strategies, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-411, https://doi.org/10.5194/iahs2022-411, 2022.

Hill reservoirs are small dams intercepting stream runoff in headwater catchment. These reservoirs have been increasingly used in arid and semi-arid regions, in order to provide water for irrigation and farming. Understanding the hydrological functioning of these reservoirs and especially the losses due to infiltration through the reservoir bed is important in order to improve reservoir management practices notably in mediterranean basin threatened with climatic change and water scarcity.

The present work aims to explore numerically the dynamic of infiltration through the reservoir bed in relation to the water level variation in reservoir. The approach is based on a modeling study of a 2D flow model with the Hydrus model. The simulated domain represents a longitudinal section of the hill reservoir. Different scenarios with three different forms of variations of the daily water level in the reservoir were tested. We also considered different hydraulic properties of porous media underlying the reservoir bed to analyse their effects on the infiltration rate.

The monthly dynamics of simulated infiltration rate in real conditions was consistent with the monthly infiltration estimated in Bouteffeha et al., (2015) based on a hydrological water balance approach. Furthermore, daily infiltration rate seems to vary according to the variation of the reservoir water level. For all scenarios of reservoir water level dynamics and hydraulic properties, the numerical exploration shows that the relationship between infiltration rate and daily water level is hysteretic, involving different infiltration rates for the rising and the recession phases for given water level . As a consequence, linear relationship usually used in hydrologic model to simulate infiltration from reservoir may lead to significant errors, particularly during the rising phase in the wet season when the reservoir is filling up.

References:

Bouteffeha, M., Dages, C., Bouhlila, R., et Molénat, J. (2015). A water balance approach for quantifying subsurface exchange fluxes and associated errors in hill reservoirs in semiarid regions. Hydrological Processes, 29(7), 1861-1872

How to cite: Bouteffeha, M., Dages, C., Molénat, J., and Bouhlila, R.: Numerical exploration of the dynamics of infiltration in hill reservoir, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-472, https://doi.org/10.5194/iahs2022-472, 2022.

Salinization is a worldwide issue particularly threatening arid and semi-arid soils. Primary salinization is due to unbalanced flows between upward water and solute flows leading to salts accumulation and downward flows which allow the leaching of salts. Soil salinity affects vegetation by causing osmotic and toxic stress. In return, soil water transfers are impacted since water extraction by plants is limited. Salinity leads also to a decrease of soil hydraulic conductivity.

Salinisation is often described as a threat to agriculture, but less as a driver of specific ecosystem functioning, such as salt marshes. These interfaces between land and sea are very present in the Mediterranean deltas and lagoon complexes, and provide several ecosystem services, (e.g. being the natural areas among with the highest carbon storage rate). Salinity in these ecosystems is highly dependent on freshwater inputs from precipitation, natural or anthropic flooding, making them vulnerable to global changes. Nevertheless, the effects of flooding on hydrological dynamics and solute transfers in salt marshes are not well known.

We choose a study site in the lowlands of the Aude river (the Castelou site, Narbonne, France) to address the question of the hydrological behavior of a salt marsh managed by different flooding intensities in relation to plant communities. Soil moisture, saturated zone depth, and salinity dynamics are monitored by a set of continuous and point measurements at 12 sites distributed along a flood management gradient and a natural salt pressure gradient. Based on these observations, time continuous data series have been built by a physics-based modeling. The analysis provides a better understanding of the effects of flooding on soil water and solute stocks and fluxes, and relates them to the specific composition of plant communities.

We show that flooding has varying effects on water storage in unsaturated and saturated zones. Soil water recharge has a small effect on soil salt content on an annual scale but limits the level of osmotic stress. In the absence of flooding, osmotic stress is more pronounced, altering the specific composition of plant communities, suggesting changes in their functional properties.

How to cite: Berteloot, V., Crabit, A., Barkaoui, K., Kazakou, E., and Colin, F.: Hydrological behaviour of mediterranean salt marshes and implications for vegetal cover, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-287, https://doi.org/10.5194/iahs2022-287, 2022.

Sediment transport is linked to socio-economic issues, including reservoir siltation, dam storage loss, arable soil loss, terrain quality deterioration, and land productivity decline. In semi-arid regions (e.g., north of Algeria), the climate often alternates between long periods of drought and sporadic floods. Sediment production steadily occurs during dry periods as a result of various processes that disturb the soil, and it is greatly increased during a rainfall episode, due to the rain-splash effect. During a flood, heavy sediment transport occurs because of sediments originating from both the basin and hydrographic network. Consequently, to prioritize management strategies, sediment dynamics and sources contribution assessment are needed. While many methods to quantify sediment source contributions are available, their applicability is restricted by financial limitations, data availability, and suitability. So, more suitable methods are required. In this work, a rapid integration method is presented. This approach aims to separate and quantify sediments originating from the hydrographic network by water erosion and sediments supplied from the catchment, in-channel storage, and accidental processes. The required data is limited to continuous or semi-continuous sediment concentration-discharge measurements (including turbidity-based sediment concentration). The method is validated and tested for several basins, including watersheds from humid regions, to verify whether it can be generalized.

How to cite: Khettab, O. E. F. and Megnounif, A.: Sediment transport and origin in Mediterranean semi-arid basins: Sediment dynamics assessment and quantification, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-515, https://doi.org/10.5194/iahs2022-515, 2022.

A consequence of climate change, less investigated from the hydrological point of view, is the alteration of the frequency and intensity of forest disturbances that can reduce forest productivity, change the distribution of tree species, and shift their range and density. Based on this, this study evaluates the ability of remnants of native forests to resist or adapt to a changing climate. The case study is the island of Sardinia, located within the Mediterranean basin. Sardinia covers a latitudinal gradient of 300 km; and it is one of the least populated and the most forested regions in Italy. It is considered one of the most important biodiversity reservoirs inside the Mediterranean hotspot. From one hand Sardinia is experiencing a decreasing pressure on forests due to human factors, from the other, some studies demonstrate that winter precipitation and runoff are decreasing alarmingly, and this can have an impact on forests. Based on the above, this study aims, through the analysis of 20 years of satellite images (MOD44B), to evaluate forest cover changes and to detect any possible relationship with some of the most important climate variables such as precipitation (96 years daily data), air temperature and vapor pressure deficit (40 years of data). Results indicate that in the last 40 years Sardinia has experienced a simultaneous increase in air temperatures (0.026 °C*y^-1) and VPD (0.001 kPa*y^-1) combined with reductions in both total precipitation (-14.03 mm*y^-1) and winter precipitation (-12.09 mm*y^-1), and that the areas with a mean annual precipitation lower than 700 mm went from the 26% in the period 1922-1979, to 63% during 1980-2018, and in effect 1980 was detect as changing point for annual precipitation. These climatic variations have led to an important reduction of the tree cover in some historical forests of Sardinia, and in the broad-leaved ones particularly. The reduction in TC shows a positive correlation with mean annual precipitation (ρ= 0.66) and altitude (0.72), while negative correlations were detected with temperature (ρ= -0.57) and VPD (ρ= -0.48). Results highlight that forests are adapting to climate change, and this may have an impact on local water resources.

How to cite: Cipolla, S. S. and Montaldo, N.: Spatiotemporal evolution of forest cover and of historical climate data: a case study in the Mediterranean basin, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-635, https://doi.org/10.5194/iahs2022-635, 2022.

The wadi Ambouli is at the origin of rare and severe flash floods with increasing frequency in recent years. These floods are responsible for a lot of damage including human lives and good losses. Moreover, the aquifer located in the south-eastern part of the wadi Ambouli watershed (794 km²) is essential as the main source of drinking water for the city of Djibouti. Therefore, knowledge and prevention of flows events are of primary relevance for the development and flood prevention of the city of Djibouti neasted downstream to the wadi Ambouli.

Within the framework of the management of the urban expansion of the city, it is necessary, in the long term, to set up a hydrological model in order to model the flow and flood processes and to better understand the groundwater/surface water dynamics. A special focus is needed toward the extreme events.

To overcome the few rainfall available data, remote sensing techniques have been used to provide more representative information on rainfall spatio-temporal distributions. We present here a comparative study of rainfall data from 15 satellite products with those from rain gauge stations located in the wadi Ambouli watershed.

The analysis is conducted on various time steps, annual, monthly and daily, at the spatial scale from the Ambouli watershed (794 km²) to the point scale (comparison of point rainfall station and satellite grid). The comparisons of time series are based on the correlation coefficient r with the corresponding p-value and the Kling Gupta Efficiency (KGE) criterion.

The first results at annual and monthly time steps show that 5 satellite products present a high correlation coefficient and KGE with ground rainfall data (EWEMBI, GPCC, JRA_55_Adj, MSWEP and WFDEI_GPCC). For the Djibouti Aerodrome station, which is the one with the longest temporal data, the satellite products EWEMBI, JRA_55_Adj, and WFDEI_GPCC provide the best estimates of rainfall depth (annual scale). The MSWEP product (with r = 0.76) underestimates the annual rainfall over almost the entire study period.

How to cite: Moussa Omar, G., Paturel, J.-E., Salles, C., Mahe, G., Jalludin, M., Satge, F., Ismail Nour, M., and Hassan Hersi, A.: Rainfall from ground-based rain gauges vs satellite products at different time steps in the southeast of the Republic of Djibouti, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-64, https://doi.org/10.5194/iahs2022-64, 2022.

Coastal lagoons are biodiversity hotspots, but often affected by human pressure like high nutrient and sediment loads from intensive agriculture and negative impacts from tourism and urban expansion. The Mar Menor (southeast Spain) is the largest salt water lagoon of Europe, however, in recent years the lagoon has been subject to a substantial loss of its biodiversity due to increasing human pressure from the surrounding Campo de Cartagena catchment. The Campo de Cartagena is characterized by a semi-arid climate with long dry spells and infrequent, but extreme, precipitation events. Since the opening of the inter-basin water transfer Tajo-Segura in 1979, the area of intensive irrigated agriculture has progressively increased, from around 10% in 1977 to 45% in 2020. The aim of this study is to evaluate the impact of these historical land use changes on a range of hydrological and soil erosion indicators. These indicators include irrigation water demand, plant water stress, soil erosion, sediment yield, among others. We also evaluated an adaptation strategy by creation of a 1.5-km green buffer surrounding the Mar Menor lagoon consisting of wetlands with the aim to catch sediments before they can enter the Mar Menor. We applied the hydrology-soil erosion model SPHY, which simulates the most relevant hydrological and soil erosion processes, including irrigation and sediment transport. The model results show that historical land use change caused a substantial increase of irrigation water demand (+209%), sediment yield (+42%) and flood discharge (+115%), which negatively impact the scarce water resources, the water quality of the Mar Menor lagoon and flooding of urban areas. The Green buffer scenario has the potential to decrease the impact on the Mar Menor through a significant reduction in sediment yield towards the lagoon. This work has been financed by ERDF/Spanish Ministry of Science, Innovation and Universities—State Research Agency/Project PID2019-109381RBI00/AEI/10.13039/501100011033 (XTREME) under the National Program for Research, Development and Innovation focused on the Societal Challenges and the Horizon 2020 project COASTAL (Collaborative land-sea integration platform, grant agreement 773782).

How to cite: Eekhout, J., Albaladejo, J., Martínez-López, J., Castillo, V., and de Vente, J.: Evaluating the impact of irrigated agriculture on a coastal lagoon in a semi-arid catchment in southeast Spain, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-749, https://doi.org/10.5194/iahs2022-749, 2022.