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Isotopic tracers to assess the snowmelt contribution to the groundwater recharge: a case from the Moroccan High and Middle Atlas Mountains
Abstract
The significantly high water stress affecting Morocco during the past decades was an impact of drought and overexploitation of water resources. Therefore, assessment of these resources for better water management is a necessity. In our context, the High and Middle Atlas Mountains are the main contributors of downstream feeding within the country. The objective of this study is to assess rainfall and snowmelt runoff supplying groundwater of the aforementioned regions using the stable isotopes approach. Sampling campaigns and chemical and isotopic analyses were carried out in the Ourika and High Oum Er-Rbiaa sub-catchments, belonging to the great Tensift and the Oum Er-Rbiaa basins respectively. The snowmelt sampling in the Ourika basin was effectuated in two ways: the polyvinyl chloride snow cover boring and the passive capillary samples. The isotopic data of the Ourika basin allows estimating a recharge altitude between 2000 and 3000 m, following an altitudinal gradient of 0.27‰/100m. The contribution of rainfall and snowmelt in groundwater recharge using the isotopic mass balance model suggests a snowmelt recharge rate of 47% while rainfall supplies about 53%. The isotopic preliminary results from the HOER catchment indicates that all samples are close to global and local water meteoric lines suggesting their common origin from the Atlantic air masses, and recharge altitude varies between 1600 and 2900 m according to a gradient of 0.27‰/100 m. Ultimately, this study reveals the usefulness of environmental tracers to assess the endmembers contributions (snow and rain) to groundwater recharge at the catchment scale.
... These studies employ hydrogeological, hydro-geochemical, and isotopic methods to understand the origin of water, associated groundwater recharge processes, and conceptualize the groundwater flow within the major aquifer systems in many areas in Morocco. On the other hand, the contributions of precipitation (rain and snow) in the High Atlas and neighboring plains have been established by other authors in the Souss basin (Bouchaou et al., 2008;Bouragba et al., 2011;N'da et al., 2016), in the Haouz aquifer (Rhoujjati et al., 2021), and in the Draa basin (Cappy, 2006;Warner et al., 2013;Khettouch et al., 2023). The contribution of snowmelt varies between 42% and 80% in the different areas studied (N'da et al., 2016;Cappy, 2006). ...
... These tools of hydrogeological, hydro-geochemical, and isotopic methods to understand the origin of water, and associated groundwater recharge processes and conceptualize the groundwater flow within the major aquifer systems in many areas in Morocco, were contributed significantly to clarify the functioning of groundwater in the areas where a systematic monitoring is lacking. On the other hand, the contributions of precipitation (rain and snow) in the High Atlas Mountains and neighboring plains have been established by other authors in the Souss (Bouchaou et al., 2008;Bouragba et al., 2011;N'da et al., 2016), in the Haouz aquifer (Rhoujjati et al., 2021) in the Draa basin (Cappy, 2006;Warner et al., 2013) and in the Middle Atlas Mountains . This statement confirms very well the important role of the Moroccan Atlas and Rif Mountains in the recharge of the major hydrological basins through the country. ...
... This unique isotopic composition allows for tracing the contribution of snow to hydrological catchment pathways (Earman et al., 2006;Pavlovskii et al., 2018). Previous studies conducted in the High Atlas Mountains using isotopic techniques have revealed varying contributions of snowmelt to groundwater recharge, ranging from 47% to 80%, depending on factors such as catchment size, land use, and geological characteristics (Cappy, 2006;N'da et al., 2016;Rhoujjati et al., 2021). Additionally, hydrological modeling has indicated that approximately 25% of streamflow originating from the North of the High Atlas Mountains is derived from snowmelt (Boudhar et al., 2009). ...
... s.l (Bell et al., 2022). The annual snow cover surface in the Ourika sub-catchment during the past decade varies between 11.4 km 2 in 2013 and 44 km 2 in 2018 (Rhoujjati et al., 2021). ...
Study region: The Atlas Mountains of Morocco, specifically the High Oum Er-rbiaa (HOER) and Ourika catchments. Study focus: to identify the recharge processes within the semi-arid watersheds, in the Atlas Mountains, through monthly monitoring of snow, rainfall, surface water, and groundwater isotope signal, but also the usage of remote sensing data. New hydrological insights for the region: The spatial-temporal analysis of groundwater and precipitation isotopes reveals significant spatial heterogeneity, primarily influenced by the geological variations in each aquifer. Temporal variations indicate that direct recharge occurs in response to winter precipitation, whereas a delayed response is observed during the summer when snow replenishes groundwater towards the end of the melting season. The findings are further supported by the "Gravity Recovery and Climate Experiment" (GRACE) dataset, which demonstrates that high values of Total Water Storage (TWS) align with groundwater isotopes. This highlights the substantial groundwater abstraction rate between March and June to compensate for the lack of precipitation during this period. The analysis of isotope data indicates that 50% of groundwater recharge in the upstream Jurassic aquifer and 80% in the downstream Triassic-Paleozoic aquifers in the HOER catchment is sourced from snowmelt. Similarly, in the Ourika catchment, snowmelt contributes 30% and 50% of groundwater recharge in the upstream and downstream portions of the catchments respectively. This disparity is due to different melting rates across altitudinal ranges and variations in the lithology of each catchment.
... In the Western Mediterranean, specifically Morocco, several studies were carried out using isotopic tracers for water resources and climate including precipitation investigation in many areas (Bouchaou et al. 2008(Bouchaou et al. , 2017Celle-Jeanton et al. 2001;Hsissou and Mohamed 2007;Hssaisoune et al. 2019;Tagma et al. 2009). However, only a very limited number of works were focused mainly on isotopic signatures in precipitation and associated processes (Cappy 2006;N'da et al. 2016;Ouda et al. 2005b;Rhoujjati et al. 2021). Ouda et al. (2005a) monitored three meteorological stations across Morocco which disclosed both Atlantic and Mediterranean origins of precipitation. ...
... However, the scarcity of the data limits the understanding of the precipitation processes. Cappy (2006Cappy ( ), N'da et al. (2016 and Rhoujjati et al. (2021) investigated rainfall and snow in the High Atlas. Ait Brahim et al. (2016) provided a review focusing on 17 rain gauges in Northwest Africa which exposed the role of the Atlas Mountains, acting as a topographic barrier which limits the passage of humid air masses from the Atlantic Ocean. ...
Morocco, being part of the Mediterranean basin, is characterized by a semi-arid climate heavily affected by climate change, spatial heterogeneity of the water resources along with its high demand. As the region heavily relies on precipitation to supply surface and groundwater, the restraints are a capital threat to its availability. Therefore, conducting studies on the spatio-temporal variations of precipitation ought to be a necessity. Herein, we present the results of our study conducted in the High Oum-Er Rbiaa catchment in the Moroccan Middle Atlas Mountains. Spatial and temporal monitoring of precipitation isotopic composition during a full hydrological year indicated a wide variation of isotopic values ranging from – 3.7‰ to – 13.1‰ and from – 17.1‰ to – 78.2‰ for δ¹⁸O and δ²H, between winter and summer respectively. Deuterium excess was marked by a strong seasonality, ranging from -9.2‰ to 27.8‰, with a mean value of 14.8‰. The preliminary local meteoric water line (LMWL: δ\updelta²H = 6.58 × δ\updelta¹⁸O + 8.3 (R² = 0.92)) reflects the significant evaporation effect, whereas the high d-excess values might also suggest Mediterranean-sourced moisture. Global reanalysis data of the vertical integral of moisture flux combined with air masses trajectories simulations, confirm substantial Mediterranean-sourced moisture during the rainiest events in 2020–2021, as shown by the depleted isotope values (– 9.5 < δ¹⁸O (‰) < – 13.1; – 55 < δ²H (‰) < – 78.2) and high d-excess (18 < d-excess (‰) < 27). Contrariwise, summer precipitation displays weak and heterogenous moisture sources indicative of continental influence, as reflected by the enriched isotope values and high d-excess (0 < d-excess (‰) < 5) likely due to sub-cloud evaporation process. The findings allowed to emphasize the influence of large-scale water vapor transport of oceanic moisture contributing to winter precipitation within the region, whereas summer precipitation is affected by cloud microphysical processes generating local rainfall.
... This is particularly evident in many Moroccan watersheds, where snowmelt contributes between 15 % and 50 % of annual flow (Boudhar et al., 2009). Furthermore, recent studies highlight the vital role of snowmelt in groundwater recharge, with contributions ranging from 30 % to 80 % in various Atlas Mountain catchments (N'da et al., 2016;Rhoujjati et al., 2023Rhoujjati et al., , 2021. In addition, climate projections for Morocco suggest a significant decrease in winter precipitation, with a 15 % reduction expected by 2050 (Driouech et al., 2010) and a decrease in annual precipitation of up to 34 % for the period 2039-2065 (Hadri et al., 2020). ...
In semi-arid Mediterranean areas, a significant proportion of the population living downstream depends on water resources from snowmelt and precipitation as their main source of water. Consequently, snow-covered mountain regions can be considered as a vital water tower, providing a steady supply of water, and contributing significantly to streamflow and groundwater recharge. Given the scarcity of ground-based hydroclimatic measurements, remote sensing could be an effective technique for mapping and monitoring snow cover. This study evaluates the last version of MODIS (version 6, called V6) snow cover product, optimizing the NDSI threshold for accurate snow cover mapping and developing models for local fractional snow cover estimation in the southern Mediterranean region, particularly in the Moroccan Atlas Mountains. For this purpose, 448 Sentinel-2 (S2) scenes from six different regions across the Atlas Range were used to adjust the NDSI threshold and to develop FSC estimation models. In addition, a total of 8419 MOD10A1 images from March 2000 to June 2023, and 7561 MYD10A1 images from September 2002 to June 2023, were processed to improve cloud filtering and to develop a highly accurate daily snow cover product suitable for the Moroccan Atlas Mountains. The cloud correction approach significantly reduced the number of cloud-covered pixels, from 25.7% to 0.4% after filtering. Two schemes for selecting the MODIS NDSI threshold were tested: (1) the global reference of 0.4 and (2) the locally optimal threshold of 0.2. The average snow cover estimation errors using the optimal and global NDSI thresholds for Terra are an average overestimation of 0.34% and a significant underestimation of 6.13%, respectively. For Aqua, the corresponding errors are an overestimation of 1.4% and an underestimation of 6.8%. Thus, the optimal NDSI threshold of 0.2 could be more appropriate than the threshold of 0.4 for use in the southern Mediterranean region. The new FSC estimation models developed showed satisfactory performance with significant correlation coefficients (mean of 0.85 for Terra and 0.83 for Aqua), and with low RMSE and MAE values (mean of 0.17 and 0.12 for Terra and mean of 0.19 and 0.14 for Aqua) when comparing FSC derived from high-resolution S2 data with predicted FSC from MODIS NDSI. The daily snow cover product developed was compared with the high-resolution snow maps obtained from S2 satellite imagery in different regions of the Moroccan Atlas. On average, the product showed a mean correlation coefficient of 0.96, a mean absolute error of 0.22%, and a mean reasonable negative bias of −0.17%. This research concludes that the enhanced daily snow cover product could improve the understanding of spatiotemporal dynamics of snow extent and, therefore, contribute to quantifying the snowmelt contribution to the water budget through modeling approaches in the southern Mediterranean region.
... In contrast, the deeper aquifer is most likely recharged in the Jbel Kourati and Jbel Hadid Mountains, where the elevations range from 242 to 800 masl, or during a wet period with a distinctly negative isotopic signature. These observations have been made in other regions of Morocco (Bouchaou et al., 2009;Ettayfi et al., 2012;Hssaisoune et al., 2019Hssaisoune et al., , 2022Khettouch et al., 2022;Qurtobi et al., 2010;Rhoujjati et al., 2021;Tijani et al., 2022;Warner et al., 2013). ...
The Tadla plain located in the Oum Er-Rbia River Basin constitutes one of the principal agricultural production areas in Morocco. The groundwater resources are derived from the karst aquifer of the Atlas Mountains and the multilayered system (superficial and deep aquifers) of the Tadla plain. The Turonian constitutes the main productive aquifer in the area. The isotopic composition and concentration of strontium in 43 groundwater samples, combined with solute concentration data, provide important details regarding groundwater geochemical evolution, flow pathways and mixing processes in the Tadla multilayered aquifers. Shallow aquifers are characterized by significantly higher salinity, particularly in irrigated perimeter areas (Beni Amir and Beni Moussa). The relationship between chloride and EC shows a similar correlation for all water groups, except for some Atlas springs with conspicuously lower chloride/EC ratios. Stable isotopes suggest that the waters originated from meteoric water that was infiltrated into the different aquifers through permeable formations without secondary surface evaporation. The strontium isotope ratios of low saline water from the Turonian aquifer and the High Atlas spring waters overlap and show mixing (0.7078–0.7092) between Sr derived from the Turonian age limestone aquifer (0.703) and a higher 87Sr/86Sr source. Two types of chloride saline water were found in all aquifers: (i) low 87Sr/86Sr (0.7078) and Br/Cl (1.7 × 10–4) source that affects groundwater in the Turonian and Senonian aquifers. This type of water is originated from the dissolution of gypsum and halite deposits. (ii) High 87Sr/86Sr (0.7110) and marine Br/Cl (~ 1.5 × 10–3) source that occurs mostly in the Eocene aquifer.
... According to Jasechko (2019), annual precipitations characterized by d 18 O isotope signature heavier than groundwater are suggestive of a variety of recharge conditions, such as higher recharge altitudes (Gonfiantini et al., 1976), recharge biased to wet seasons or irrigation return flow (Williams & Rodoni, 1997). The hypothesis of higher recharge conditions is fairly emphasized in previously published data (Rhoujjati et al., 2021), by the usage of the altitudinal gradient of −0.27‰ (Bouchaou et al., 1995). The recharge altitude for the sub-catchment oscillates between 1600 and 3200 m. ...
Morocco is characterized by a semi-arid to arid climate, except for a humid zone in the North. This climatic restraint, accentuated by climate change and the high demand for water resources, requires the application of new approaches to complement conventional hydrological methods that will help to improve water assessment and management strategies. Among these approaches, stable isotopes allow to understand the different processes involving groundwater or water resources in general. The Atlas Mountains are an important supply of surface and groundwater, with a significant portion stemming from the snow cover. Hence, this work seeks to quantify the snowmelt contribution to surface water and groundwater recharge in the High Oum Er-rbiaa (HOER) through the Middle Atlas Mountains, by adopting the approach of stable isotopes. The methodology consisted in collecting surface, groundwater, precipitation and snow cover during an entire hydrological year. Preliminary findings are unveiled, as follows: the extensive isotope values of precipitation compared to surface and groundwater were revealed to be an indicator of a variety of recharge conditions, such as high altitude and temperature. Further assessment of the recharge altitude following an altitudinal gradient of − 0.27%/100 m indicated a recharge altitude between 1600 and 3200 (m asl).
... In contrast, the deeper aquifer is most likely recharged in the Jbel Kourati and Jbel Hadid Mountains, where the elevations range from 242 to 800 masl, or during a wet period with a distinctly negative isotopic signature. These observations have been made in other regions of Morocco (Bouchaou et al., 2009;Ettayfi et al., 2012;Hssaisoune et al., 2019Hssaisoune et al., , 2022Khettouch et al., 2022;Qurtobi et al., 2010;Rhoujjati et al., 2021;Tijani et al., 2022;Warner et al., 2013). ...
In many coastal areas in Morocco, groundwater (GW) constitutes an important water supply for human activities. Intensive pumping makes GW highly susceptible to contamination, affecting its quality and then human health. This work aims to assess and improve the application of environmental isotopes in exploring the connections between GW recharge and discharge, as well as to identify the direction, age, and speed of GW flow, in the coastal aquifer system of the Akermoud plain. A total of 23 boreholes and wells were sampled during two sampling campaigns in 2017 and 2018, including 11 samples from the shallow aquifer and 12 samples from the deep aquifer. A set of chemical and isotopic tracers (δ ¹⁸ O, δ ² H, ³ H, δ ¹³ C, ¹⁴ C, and ³ He) is used to track water and solute from input to output of the investigated system. Stable isotopes distinguish recharge at different altitudes for the shallow and deep aquifers. Both aquifers reveal consistently low values of ³ H (between 0.3 and 0.9 tritium units) and from 28% to 64% of modern carbon for six boreholes. According to ¹⁴ C correction models, GW has ages ranging from 3300 to 11,000 years before present. GW flows from SSE to NNW and discharge along the Atlantic coast of Akermoud plain with a velocity ranging from 0.41 to 1.8 m/year.
Practitioner Points
The use of environmental tracers helps determine the origin of salinity and identify the recharge area.
Investigating the MRT of groundwater resources is essential, especially in arid regions.
Evaluating the efficiency of isotopic tracing is crucial in assessing the risk of groundwater contamination.
The findings provide insights for stakeholders to promote more sustainable groundwater management in coastal areas.
... Water scarcity in semi-arid regions is a major concern, as these regions are characterized by limited precipitation and high evaporation rates (Ait Brahim et al., 2017a;Boughdadi et al., 2023;El Bouazzaoui et al., 2022;Hakam et al., 2022a;Lautz, 2008;Rafik et al., 2023). Drought episodes exacerbate the situation, leading to a decrease in the amount of water available for populations, agriculture, and industries (Abahous et al., 2018;Dogramaci et al., 2012;Ez-zaouy et al., 2023;Ouarani et al., 2021Ouarani et al., , 2020Qadir et al., 2003;Rhoujjati et al., 2023aRhoujjati et al., , 2021. Extensive research has been conducted worldwide on this issue (Ait Brahim et al., 2019;Barnett et al., 2005;Bennani et al., 2016;Calow et al., 2010;Danni et al., 2019;Feitelson and Tubi, 2017;Malki et al., 2017;Ouatiki et al., 2022;Piao et al., 2010;Sun et al., 2013). ...
Study region: The upstream part of the Essaouira basin, a data-scare region in Morocco, Northwestern Africa.
Study focus: The scarcity of hydro-climate data is a significant challenge found in several regions worldwide, where qualitative and quantitative water resource information remains limited. Estimating and predicting groundwater levels (GWL) in such areas is a significant challenge in producing knowledge for effective water resource management. To address this issue, the present study aimed to use the Soil and Water Assessment Tool (SWAT) model in conjunction with downscaled total water storage (TWS) data (9 km) obtained from Gravity Recovery And Climate Experiment (GRACE) and machine learning techniques, specifically random forest (RF) and support vector machine (SVM), to estimate and predict the variation in GWL.
New hydrological insights for the region: This study constitutes a first of its kind in the study area; the SWAT model was set up for 10 years, with a warm-up period from 2000 to 2001, calibration from 2002 to 2007, and validation from 2008 to 2010. The statistical indices (Coefficient of Determination (R2) ≥ 0.73, R2 ≥ 0.78, Nash–Sutcliffe model efficiency coefficient (NSE) ≥ 0.67, NSE ≥ 0.80 respectively for calibration and validation) highlight a significant correlation, implying the model’s capability to faithfully reproduce the streamflow. The downscaled TWS demonstrates an impressive ability to identify and monitor fluctuations in GWL. Using machine learning algorithms (RF and SVR), the prediction of GWL yielded satisfactory results, NSE = 0.78 and root mean square error (RMSE) = 0.33, NSE = 0.51 and RMSE = 0.49 for the RF and SVR, respectively. Despite some limitations, our approach provided promising results in GWL prediction, with the possibility of expanding to other data-scarce regions.
... At the beginning of the ablation period, meltwater infiltrates into the soil and resides there temporarily prior to large-scale drainage through the surface soil layers. Because of this complexity, environmental tracers are critical and limited to favorable for site-dependent estimations on catchment scale (Rhoujjati et al., 2021). The isotopic evolution by the model may would be limited to only applying in smallscale watershed meteorologically well-instrumented locations. ...
Snowmelt, a component of the hydrological cycle, is influenced by changing climate and meteorological events. In the context of hydrometeorological studies, the water isotopic composition of snowmelt has been commonly used. This study examined temporal variations in the isotopic composition of snowmelt from an isotopically heterogeneous snowpack to the context of accurate quantification of isotope-based hydrograph separation. In this study, a one-dimensional model was used to simulate the isotopic variations of the meltwater by varying the initial isotopic compositions of the snow layers and parameters such as effectiveness of exchange (ψ), ice-to-liquid ratio of the exchange system (f), and water saturation (S). Isotopic evolution is sensitive to the initial layer sequence of isotopically enriched or depleted snow in the snowpack and the extent of isotopic differences between the layers. More variated patterns are observed in the isotopic evolution as the ψ and f values are increased; particularly, a significant modification is observed in the bottom layer that is altered by the enriched top layer, thereby further affecting the pattern of isotopic evolution. The isotopic heterogeneity has been suggested to be a significant factor in the isotopic evolution of snowmelt, even though various other influencing factors have been considered under natural conditions. Because of the close dependence of snow and glacial conditions upon climate change, this study is expected to support further hydrometeorological studies, particularly in snow-dominated regions.
... where X and 1-X are the contributions of A and B to the mixture, respectively. In the Moroccan context, the same equation was used to give a rough estimation of potential contribution of end-members (rainfall, snowmelt and surface water) to groundwater recharge (N'da et al., 2016;Rhoujjati et al., 2021;Rafik et al., 2022). In the present study, Eq. (1) is applied to estimate the contribution of rainfall and surface water to groundwater recharge based on groundwater δ 18 O data from 2004, 2006, 2018 and 2020 sampling campaigns. ...
Study region: The downstream part of the Essaouira basin, Morocco, Northwestern Africa.
Study focus: This study combines multivariate statistical analyses, stable isotopes, hydro-geochemical, hydrogeological, geological and remotely sensed data to gain a better understanding of the hydrological and groundwater salinization processes in a coastal aquifer. Hydrogeochemical data from 223 samples as well as stable isotope data collected during 10 sampling campaigns between 1990 and 2020 were compiled and subjected to a comprehensive analysis. Groundwater recharge obtained from the stable isotope approach was checked using a water balance method based on remote sensing data of actual evapotranspiration.
New hydrological insights for the region: Seawater intrusion was detected only for the period of 2009-2020, nearby the ocean, whereas hyper-salinity due to evaporite dissolution occurred throughout the entire period (1990-2020) primarily in the southern part of the aquifer. Additionally , the isotopic mass balance model shows that aquifer recharge from the Ksob river area is mainly located in the northeastern region. Furthermore, based on average values of stable isotopes of rainfall and groundwater, preliminary results show that only months of November, December and January with rainfall higher than 54 mm contribute to groundwater recharge. The water balance approach confirmed these results, but also revealed a lower recharge in February, with a monthly average precipitation of 46 mm. The outcomes of this research enabled the construction of a comprehensive conceptual 3D model of the Essaouira coastal aquifer. The insights from this research are important to guide measures for sustainable water resources management.
... The "long-term groundwater recharge estimation is indispensable to address the abovementioned problems" of water resources in dry regions (Hassen et al. 2021;Zhang et al. 2020). The methods of recharge estimation are broadly classified as numerical (Hartmann et al. 2017), physical (Nimmo et al. 2015), chemical (Salem et al. 2022;Rhoujjati et al. 2021;Mensah et al. 2014), or a combination (Zhu et al. 2020). Various specific methods were used by the researchers to estimate groundwater recharge globally (Fabio et al. 2022;Twihri et al. 2022;Tiwari et al. 2021;Khan et al. 2021). ...
Irrigation development is crucial to satisfy the rising food demands of the growing worldwide population. This is mainly imperative in dry regions where “crop water requirements are largely met by supplemental irrigation due to poorly distributed and erratic rainfall. Irrigation development is also essential for accomplishing many UN’s SDGs” such as “SDG2 (Zero Hunger), SDG3 (Good health and well-being), and SDG15 (Life on Land).” However, “without proper management, irrigation development can cause twin water resource issues, i.e., rising water tables and salinization in irrigated dry regions.” A long-term groundwater recharge estimation is indispensable to manage the abovementioned problems. This study develops and employs a simple water balance model to estimate the long-term (40 years, e.g., from 1979 to 2019) seasonal groundwater recharge for evaluating the rising water tables in a study region of India. “The investigation is the first in the study region and is easy to follow, and it can also be replicated in other regions of the world dealing with similar problems. The analysis disclosed that the developed model performs very well in estimating the groundwater recharge.” This is also verified statistically by the high R-squared (0.959) and model efficiency (0.956) values and low ME (0.0183 m) and RMSE (0.1178 m) values. The analysis divulges that the study area receives a normal net recharge of 5.9 Mm3 that causing a normal yearly water table rise of 0.13 m throughout the study period. Since the water table is by now high, a further rise would aggravate the situation. Alternative management plans should be considered for sustainable water management in the region. As a follow-up action, four potential alternatives were studied using the developed model. The analysis of the alternatives disclosed that rice areas should be reduced and substituted with other crops with low water requirements as the latter would have lower seepages which are needed to maintain a favorable water balance. Similarly, the conjunctive use of water resources requires to be augmented for irrigating crops which supports more groundwater draft from the region. The other alternative proposes the implementation of improved irrigation methods, i.e., sprinkler and drip, to mainly irrigate the non-rice crops as it would reduce the substantial water losses to the groundwater system which is associated with the conventional surface-flooding irrigation method. The analysis implies that realizing a combination of multiple changes altogether would be more beneficial as compared to the distinctive changes in baseline conditions.
... To estimate the contribution of the end-members (rainfall and snowmelt), we used the isotopic mass balance model (N'da et al., 2016;Bouchaou et al., 2008). Based on the average oxygen-18 values of groundwater obtained in the Souss (N'da et al., 2016;Bouchaou et al., 2008;Bouragba et al., 2011;Dindane et al., 2003), Haouz aquifer (Rhoujjati et al., 2021, Boukhari et al., 2014 and Draa basin (Cappy, 2007;Warner et al., 2013), the contributions of precipitation (rain and snow) in the High Atlas and the surrounding plains were established. ...
Study region
Atlas Mountains located in Morocco.
Study focus
Mountainous regions constitute an area of water production, while water is used in downstream plains. In Central Morocco, the Atlas Mountains represent the most important water supply in the country. The solid part of precipitation forms seasonal snowpack. Snowmelt is important for the water supply for different uses in neighbouring plains. Accurate knowledge of snow water equivalent is key information needed by policy-makers to help design and implement appropriate allocation strategies for water resource management. The objective of this paper is to provide a summary of our research activities on snow hydrology in the Atlas Mountains during the past twenty years. The approach combines in situ measurements, remote sensing, and modeling.
New hydrological insights for the region
Following a description of the context of the Moroccan Atlas Mountains and the experimental network, an overview of the main results obtained is presented: the characterization of the spatiotemporal dynamics of snow cover; the impact of the North Atlantic Oscillation on the snow-covered area; the snowmelt contribution to the flows of the Atlas rivers; the contribution of snowmelt to surface and groundwater recharge and the quantification of climate change impacts on snow and associated runoff from the Atlas Mountains. We also present challenges and future research perspectives within this topic.
This chapter is dedicated to presenting the optimization method employed, which primarily utilizes the functionalities provided by GIS (geographic information systems) and remote sensing for data structuring, cross-referencing information layers, and spatial analysis across various themes. It incorporates a multicriteria hierarchical analysis approach, enabling the integration of multiple decision criteria into a unified model. This approach involves conducting comparative evaluations of each pair of criteria and calculating their weights for the comparative assessment of each pair of options concerning each sub-criterion. Both methods employed showcase a robust multicriteria decision support tool. It is noteworthy that ensuring the validity of the SCS-CN procedure necessitates the incorporation of other supply models to enhance the accuracy of determining suitable locations for water accumulation structures.
The variations of the stable isotope compositions in water provide critical information on hydroclimatic mechanisms. The climatological and hydrological processes in the Nujiang headwaters in the central Qinghai–Tibetan Plateau are extremely complex and are controlled by alternating continental/local recycled and maritime moisture. However, previous studies have only derived limited data from different types of water in the Nujiang headwaters. Therefore, aiming to understand the sources of stable oxygen (δ18O) and hydrogen (δ2H) isotopes’ compositional variability and how these are related to hydroclimatic processes, we measured δ18O and δ2H values from surface waters, snow and precipitation across the Nujiang headwaters from April to September 2018. We found higher δ18O (−13.7‰), δ2H (−101.8‰) and deuterium excess (d-excess; 7.6‰) values in the non-monsoon season and lower values in the summer monsoon season. Our findings indicated that the δ18O and δ2H compositions were significantly affected by different moisture sources in this region. The slope (6.66) and intercept (−14.90) of the surface water line (SWL: δ2H = 6.66 δ18O − 14.90, R2 = 0.98) were lower than those of the local meteoric water line (LMWL: δ2H = 9.50 δ18O + 41.80, R2 = 0.99) and global meteoric water line (GMWL), indicating that precipitation was the primary water vapor source for surface water, and evaporation was the dominant hydrological process for the Nujiang headwaters. In general, δ18O and δ2H tended to be negatively correlated with precipitation and air temperature. In addition, δ18O and δ2H values in the Nagqu River were inversely correlated with the intensity of discharge, highlighting a precipitation-driven isotope-discharge pattern. Our findings provide a theoretical basis for the hydroclimatic mechanisms occurring in the Nujiang headwaters and further augment our understanding of the southern–middle–northern hydroclimate in the Qinghai–Tibetan Plateau.
Groundwater ¹⁸O/¹⁶O, ²H/¹H, ¹³C/¹²C, ³H, and ¹⁴C data can help quantify molecular movements and chemical reactions governing groundwater recharge, quality, storage, flow, and discharge. Here, commonly applied approaches to isotopic data analysis are reviewed, involving groundwater recharge seasonality, recharge elevations, groundwater ages, paleoclimate conditions, and groundwater discharge. Reviewed works confirm and quantify long held tenets: (i) that recharge derives disproportionately from wet season and winter precipitation; (ii) that modern groundwaters comprise little global groundwater; (iii) that “fossil” (>12,000‐year‐old) groundwaters dominate global aquifer storage; (iv) that fossil groundwaters capture late‐Pleistocene climate conditions; (v) that surface‐borne contaminants are more common in younger groundwaters; and (vi) that groundwater discharges generate substantial streamflow. Groundwater isotope data are disproportionately common to midlatitudes and sedimentary basins equipped for irrigated agriculture, but less plentiful across high latitudes, hyperarid deserts, and equatorial rainforests. Some of these underexplored aquifer systems may be suitable targets for future field testing.
Snowfall may have different stable isotopic compositions compared with rainfall, allowing its contribution to potentially be tracked through the hydrological cycle. This review summarizes the state of knowledge of how different hydrometeorological processes affect the isotopic composition of snow in its different forms (snowfall, snowpack, and snowmelt), and, through selected examples, discusses how stable water isotopes can provide a better understanding of snow hydrological processes. A detailed account is given of how the variability in isotopic composition of snow changes from precipitation to final melting. The effect of different snow ablation processes (sublimation, melting, and redistribution by wind or avalanches) on the isotope ratios of the underlying snowpack are also examined. Insights into the role of canopy in snow interception processes, and how the isotopic composition in canopy underlying snowpacks can elucidate the exchanges therein are discussed, as well as case studies demonstrating the usefulness of stable water isotopes to estimate seasonality in the groundwater recharge. Rain‐on‐snow floods illustrate how isotopes can be useful to estimate the role of preferential flow during heavy spring rains. All these examples point to the complexity of snow hydrologic processes and demonstrate that an isotopic approach is useful to quantify snow contributions throughout the water cycle, especially in high‐elevation and high‐latitude catchments, where such processes are most pronounced. This synthesis concludes by tracing a snow particle along its entire hydrologic life cycle, highlights the major practical challenges remaining in snow hydrology and discusses future research directions.
This article is categorized under:
• Science of Water > Hydrological Processes
Study of the Cenomanian-Turonian and Plio-Quaternary aquifers of Essaouira basin (Western Morocco), based on the interpretation of geochemical (major elements) and isotopic (18 O, 2 H, 13 C and 14 C) data, has aided the understanding of the hydrodynamics of these aquifers, which is greatly affected by tectonics. Hydrochemical characteristics based on the bivariate diagrams of major ions (Cl À , SO 4 2À , NO 3 À , HCO 3 À , Na þ , Mg 2þ , K þ and Ca 2þ) and electrical conductivity and mineral saturation indices indicate that the origins of groundwater mineralisation are the result of: (1) evaporite dissolution; (2) cation exchange reactions; (3) and evaporation processes. Radiogenic isotopes (3 H and 14 C) have highlighted the presence of significant recent recharge in the eastern part of the basin, with groundwater moving according to the general flow path (south-east to northwest). Stable isotope data from the Essaouira basin plot along the Global Meteoric Water Line and below the Local Meteoric Water Line. This suggests that groundwater has been recharged under several different climate regimes.
To characterize snow isotopic signatures, monitoring of snowmelt was carried out at two sites (Oukaimden and Ifni) in the Moroccan High Atlas Mountains. For the Oukaimden site, samples of snow were taken by two methods to compare sampling techniques: (1) coring with a polyvinyl chloride (PVC) tube and (2) passive capillary sampling (PCS) installed at the snow/soil interface. The analyses show variable isotope contents, ranging from −14.7 to −2.5 ‰ for oxygen-18 and from −116 to −28.2 ‰ for deuterium. The most depleted values are observed in March 2013 at high elevation (3229 m asl). The majority of snow core samples display fractionation by sublimation, whereas those collected by the PCS sampling method are close to the Global Meteoric Water Line. The isotopic signature is comparable for snow, surface water and groundwater samples, indicating that snowmelt plays an important role in recharging aquifers, lakes, and rivers on the southern and northern sides of the Atlas Mountains. Recharge by snowmelt allows the dilution of salinity in adjacent aquifers. Characterization of the stable isotopic composition of snow obtained from snow cores is limited in comparison with the PCS method, which provides realistic compositions of the melt water contribution to water resources in this semi-arid area.
The present study has analyzed the origin of recharge
and groundwater salinity in the Haouz alluvial plain, located in Central Morocco. Stable isotopic data (18O, 2H) indicate that the recharge of the alluvial aquifer is dominated by high-altitude meteoric water originating from the High-Atlas Mountains that border the plain to the south. Tritium globally indicates the presence of recent groundwater, as well as mixing between old and recent groundwater. Alluvial groundwater salinity varies from east to west. This variability is mainly induced by enrichment in chloride and sulfate salt contents. Strontium content reveals that sulfate could be related, respectively, to the influence of the Senonian carbonate deposits containing gypsum. Dissolution of halite is revealed by the plot of 18O vs Cl, where the most saline samples do not show any changes in 18O. Br/Cl ratio varies in a wide range, probably due to an orographic effect. The nitrate distribution was analyzed using indicator-geostatistical techniques resulting in probability maps. Nitrate contamination is shown to occur particularly in the eastern part of the Haouz plain. In this paper, some aspects of groundwater resources management are addressed. Different management actions are identified with regard to the current water resources status and to the land and water uses. In this framework controlling groundwater abstraction, optimizing irrigation and enhancing mountain-front recharge constitute the major key management actions that should be carried out.
Water resources in a given watershed area are mainly related to the morphology of the basin and to the prevailing climatic
conditions in the area. The exposure and orientation of the basin to rain-producing air masses are also determining factors. The watershed
of Ourika lies on the northern side of the High Atlas between 1070 m and 4001 m, with an average altitude of about 2500 m. It is well
exposed to the Atlantic humidity from the northwest, rainfall is therefore large. The slopes are also steep in the Ourika basin and the soil is
impermeable. This contrasts with the Marghène basin (upstream of oued Draa), lying on the southern part of the High-Atlas. This valley is
directed toward the south. Rainfall, slopes and altitudes are low in comparison with those of the Ourika basin. In fact, it is not exposed to
rain-producing air masses which come from the northwest. These morphological and pluviometric differences make the discharges in
Ourika basin larger than in the Marghène basin. Also, it snows on the Ourika catchment more than the Marghène’s. The snowmelt
increases spring and summer discharges and allows a perennial use of the water in the Ourika area.
Modélisation de l'érosion hydrique via les SIG et l'équation universelle des pertes en sol au niveau du bassin versant de l'Oum Er-Rbia - Morocco. The objective of the present work was to estimate soil losses in the oued Oum Er-Rbia watershed (SW Middle Atlas, Morocco). The adopted method is based on the use of Wischmeier model and geographic information system (GIS). The mean and maximum values of rainfall erosivity factor R were 90 and 119, respectively. The soil erodibility factor K is ranged from 0.01 to 0.54 (mean= 0.33). The topographical factor LS varied from 0 to 216 (mean= 16). Thecombination of different maps related to different parameters (R, K, LS, vegetation cover C and anti-erosive practices P) allowed obtaining the erosion map. The obtained results showed that the erosion affected the entire Oum Rbia watershed, but with different degrees. The mean of rate of soil loss was of 224 t / ha / year, with 45% of the basin area is subject to erosion between 50 and 400 t/ha/year mainly in areas characterized by a steep slope, high erodibility and low vegetation cover which reflects the importance of water erosion in the Oum Er-Rbia watershed.
Keywords - Oum Er-Rbia watershed, water erosion, Wischmeier model, GIS.
We modified a passive capillary sampler (PCS) to collect snowmelt water for isotopic analysis. Past applications of PCSs have been to sample soil water, but the novel aspect of this study was the placement of the PCSs at the ground-snowpack interface to collect snowmelt. We deployed arrays of PCSs at 11 sites in ten partner countries on five continents representing a range of climate and snow cover worldwide. The PCS reliably collected snowmelt at all sites and caused negligible evaporative fractionation effects in the samples. PCS is low-cost, easy to install, and collects a representative integrated snowmelt sample throughout the melt season or at the melt event scale. Unlike snow cores, the PCS collects the water that would actually infiltrate the soil; thus, its isotopic composition is appropriate to use for tracing snowmelt water through the hydrologic cycle. The purpose of this Briefing is to show the potential advantages of PCSs and recommend guidelines for constructing and installing them based on our preliminary results from two snowmelt seasons.
Le bassin versant de l’Ourika, situé dans le Haut-Atlas de Marrakech, présente une forme allongée avec des pentes très importantes au niveau des affluents et des versants. Du point de vue lithologique, il est formé de roches cristallines du socle à la partie amont, et de dépôts silteux et argileux permo-triasiques plus tendres à l’aval. Ces terrains assez imperméables augmentent les risques d’inondation. Cette situation favorise une augmentation des volumes d’eau mobilisés par le cours d'eau principal et le développement d’importantes crues. La charge solide charriée ou en suspension provient généralement des deux types de terrains soumis localement à une érosion intense. Les produits d’érosion qui sont stockés en amont, sous formes d’éboulis ou de cônes de déjection, aux ruptures de pentes des bas versants ou des confluences, sont remobilisés en périodes de crue quand les débits augmentent. Le 17 août 1995, un orage abattu en amont du bassin versant, a provoqué une crue violente et de courte durée. Cette crue dévastatrice fût consécutive à une pluie intense, couplée à un environnement géomorphologique propice au ruissellement.
The Yinchuan Plain has more than 2000 years of history of irrigation by diverting water from the Yellow River. Currently, the amount of water diverted from the Yellow River is about 21.7 times the water formed on the plain as a result of precipitation and inflow of groundwater. Under the intensive influence of irrigation, the plain changed from a desert into a rich and populous area, earning its name as ‘South China Beyond the Great Wall’, with lakes scattered across the Yinchuan Plain just as stars in the sky. In this research, 17 representative lakes were sampled to analyze and study 2H and 18O content; the results showed that lakes on the plain have undergone obvious non-equilibrium evaporation. Recharges of the lakes can be divided into three types: recharge from the Yellow River, from groundwater and from both of these. The Craig–Gordon non-equilibrium evaporation model for isotope fractionation was used to estimate the evaporation proportion of each lake. The results showed that evaporation from lakes on Yinchuan Plain is generally extensive under the dry climatic conditions. Most lakes have an evaporation proportion of over 25%, with the largest originating from Shahu lake and Gaomiaohu lake in the northern part of the plain, at 42.5% and 42.8%, respectively. The evaporation proportions calculated on the basis of 18O and 2H are very close to each other. This shows that the method used in this paper is feasible for estimating the evaporation proportions of lakes in areas with a heavy anthropogenic influence. Copyright © 2013 John Wiley & Sons, Ltd.
Waterdrops were suspended in vertical streams of N2, Ar, or He gas with relative humidities of 0, 50, and 100% to determine the effects of evaporation and isotopic exchange on the deuterium and oxygen-18 contents of the drops. Equilibrium fractionation was found to exist between a drop and vapor at its surface (even during rapid evaporation in zero humidity atmospheres), but a kinetic fractionation occurred during diffusive transport of the vapor species (H2O, HDO, and H218O) between the surface of the drop and the free atmosphere. In dry atmospheres the kinetic fractionation was given by (D/D′)n, where D/D′ is the ratio of the diffusion coefficients of H2O and HDO or H216O and H218O in the particular gas used. The exponent n was found to be in good agreement with the value obtained from studies of evaporation rates of falling drops by previous authors (n = 0.58). In moist atmospheres the kinetic fractionation depended also on the relative humidity and isotopic composition of the atmospheric vapor. Exchange adjustment times for isotopic equilibration of drops with saturated atmospheres were measured and found to be in agreement with theoretical predictions. Applications of the results to the study of atmospheric processes and isotopic fractionation during evaporation of lakes are discussed.
In this study, isotopic compositions of monthly (Global Network of
Isotopes in Precipitation), event, and intraevent rain samples are used
to examine the relationship between precipitation deuterium excess, the
type of synoptic weather systems, and associated moisture directions in
a coastal area of South Australia. The results indicate that both
synoptic weather systems and associated atmospheric moisture sources
influence deuterium excess values in precipitation. Rain events caused
by frontal systems tend to have moisture sources from the Indian Ocean
to the south of Australia. They usually have deuterium excess values of
15‰ to 25‰, depending on the moisture source direction.
Rain events caused by synoptic low-pressure and trough systems tend to
have inland moisture sources, and have a deuterium excess of 10‰
to 15‰. In addition to weather systems and associated moisture
sources, subcloud processes alter the deuterium excess in the resulting
precipitation, which is an effect that is more significant during summer
when it is warm and dry. Together, these factors contribute to the
seasonal variability of deuterium excess in the study area. Deuterium
excess of winter frontal precipitation, resulting from minimal subcloud
evaporation, is useful to infer the moisture source direction. In other
seasons, deuterium excess in precipitation is more likely altered by
subcloud evaporation. Nevertheless, intraevent samples in the middle of
a frontal event that has experienced minimal subcloud evaporation are
useful to estimate cloud deuterium excess. The results also suggest that
an abrupt change in dominant precipitation weather patterns occurs
between January and February, characterized by a sudden decrease in
δ18O and deuterium excess.
The isotopic characteristics of hydrogen and oxygen of various water bodies in the Yinchuan plain were investigated. A total of 131 water samples were collected and another 99 water samples collected by other scholars and the International Atomic Energy Agency were referred to in the study. The stable isotopic compositions of precipitation and lake waters are influenced by dry climate and strong evaporation of the area, and the slope of local meteoric water line and lake water line are smaller than that of global meteoric water line. The isotopic compositions of the Yellow River water are significantly lower than the weighted averages of local atmospheric precipitation and are controlled by the runoff of upstream areas. The isotopes of phreatic water suggest that the single phreatic water is predominantly recharged by the bedrock fissure water of Helan Mountain, while the phreatic water in multilayer structure area is recharged by multiple sources. The confined waters in the area may be recharged under cooler climate conditions than the present, which makes the heavy isotopes depleted. The 3H contents of various water bodies are in the following order: the Yellow River water > multilayer phreatic water > single phreatic water > lake water > drainage ditch water > upper confined water > lower confined water. This is in accordance with the recharge, discharge and circulation conditions of the specific water bodies. The isotope compositions of waters in the Yinchuan plain are mainly affected by external water recharge rather than local precipitation. This study is meaningful and helpful in understanding the groundwater flow systems and water cycle in the area.
Pour mieux comprendre les modalites d'alimentation des sources de l'Atlas, des campagnes de coloration et d'analyses isotopiques ont ete effectuees sur l'ensemble des sources. La disparite des circulations, la variabilite des vitesses et des taux de restitution, revelent un aquifere complexe ou a plusieurs entrees. La majorite des ecoulements convergent vers la source de Ain Asserdoune qui constitue une zone d'abaissement d'axe de plis. L'etude isotopique montre la variation des teneurs en 180 avec l'altitude des zones de recharge des differents exutoires et avec la saison. Les gradients definis autorisent la determination de l'altitude moyenne des impluviums des systemes jusqu'alors mal connus, en particulier celui de l'exutoire principal du massif, Ain Asserdoune.
Highlights
► Determine the recharge of the aquifer. ► Use isotopic and geochemical data to study the sanity origin. ► assess the residence time of water. ► Confirm the pertinence of geochemical and isotopic tools in hydrology science.
Sublimation dominates the ablation process on cold, high-altitude glaciers in the tropical Andes. Transport of water vapor through the firn and exchange with ambient moisture alter the stable isotope composition of the surface layers. A sublimation experiment carried out during an ice core drilling campaign on Cerro Tapado (5536 m above sea level, 30°08'S, 69°55'W) revealed a strong enrichment in the 2H and 18O content in the surface layer. Concerning the deuterium excess, a decrease occurred at daytime, while during the night, the values remained comparatively constant. At daytime the sublimation is enhanced due to the higher moisture deficit of the ambient air accompanied by relatively high firn surface temperatures. Low surface temperatures at night cause condensation of water vapor in the firn pores near the surface and thus inhibit penetration of the isotopically enriched surface front into deeper firn layers. Measuring an isotope profile obtained through detailed sampling between the surface and 38 cm depth proved this mechanism. The observed modification of the isotopic composition at the surface was quantitatively described by a model, which also reproduced the mass loss measured with sublimation pans and calculated from relevant meteorological data. The results of this study suggest that the influence of sublimation on the preserved isotope record of ice cores under comparable environmental conditions is rather limited. In any case, simultaneous measurements of delta2H and delta18O help to identify layers in an ice core which might be effected by sublimation. However, since the mass loss due to sublimation was of the order of 2-4 mm per day during the experiment, important palaeoinformation from an isotope record could be eliminated during extended dry periods.
A theoretical model is derived to account for the deuterium-oxygen 18 relationship measured in meteorice waters. A steady state regime is assumed for the evaporation of water at the ocean surface and the subsequent formation of precipitation. The calculations show that the deuterium and oxygen 18 content in precipitation can be taken as linearly related. From the slope and the intercept (known as the deuterium excess) of the deltaD-delta18O linear relationship for precipitation we compute the mean values on a global scale of the evaporating ocean surface temperature and the relative humidity of the air masses overlying the oceans. The deuterium excess is primarily dependent on the mean relative humidity of the air masses formed above the ocean surface. Paleoclimatic data may be obtained by this isotopic method from the analysis of old water and ice samples. A moisture deficit of the air over the ocean, equal to only 10%, in comparison to 20% for modern conditions, is deduced from the deuterium-oxygen 18 distribution measured in groundwater samples older than 20,000 years.
The 18O/16O ratio of snowmelt from a seasonal snowpack typically increases with time as the melting process progresses. This temporal evolution is caused by isotopic exchange between liquid and ice as meltwater percolates down the snow column. Consequently, hydrograph separations of spring runoff using the bulk snow composition as the new water end-member will be erroneous. Accurate determinations of the new water input should take into account the temporal variation of the snowmelt. Here we present a one-dimensional (1-D) physically based model for the isotopic evolution of snowmelt. Two parameters, the effective rate of isotopic exchange between water and ice and the ice to liquid ratio of the exchange system, are important for controlling the range and temporal pattern of the isotopic variation in snowmelt. For all plausible values of these parameters the modeled isotopic signature of snowmelt changes by 1–4‰ as snowmelt progresses. These isotopic shifts will affect the results of hydrograph separations.
The study of isotopic variation in snowmelt from seasonal snowpacks is useful for understanding snowmelt processes and is important for accurate hydrograph separation of spring runoff. However, the complex and variable nature of processes within a snowpack has precluded a quantitative link between the isotopic composition of the original snow and its melt. This work studies the isotopic composition of new snow and its modification by snow metamorphism and melting. To distinguish individual snowstorms, we applied solutions of rare earth elements to the snow surface between storms. The snowmelt was isotopically less variable than the snowpack, which in turn was less variable than the new snow, reflecting isotopic redistribution during metamorphism and melting. The snowmelt had low 18 O values early in the season and became progressively enriched in 18 O as the pack continued to melt. On a given day, meltwater 18 O was systematically lower whenever melt rates were low than when melt rates were high. The progressive enrichment in 18 O of snowmelt and the dependence of 18 O on melt rates can be explained by isotopic exchange between liquid water and ice. A one-dimensional (1-D) model of the melting process, including advection and water-ice isotopic exchange kinetics, reproduces the observed progressive 18 O enrichment of snowmelt.
The watershed of the Ourika River is a part of the Marrakech hydrosystem of the High Atlas. In the montaneous part of the watershed,
the bedrock has a low permeability, the vegetation is sparse on steep slopes and rare on the upper areas, the main valleys are narrow and deep. The N
to NW exposure favours rain falls which are usually strong, short in duration, and sometimes very intense. The conjunction of these physical and climatological
factors is at the origin of violent pulses of the Ourika River, which are characterized by high velocities and rates of flow, active erosion and
strong sediment transport. These extreme events in a semi-arid mountain setting are a repetitive phenomenon of variable intensity. The rising time of
the floods is very short and the maximum rate of flow is much higher than the mean rate.
Within the 34 years of data, floods occurred in any month of the year, excepted December. 44% of the floods occurred in spring, and 25%
in summer which is the dry season in Morocco, except in high mountain regions. These summer floods are the result of intense stormy rains, related
to a hot and stormy weather at the front of Trade winds.
The hydrograms are steep and narrow, mostly simple, monogenic and clearly distinct. They are dissymmetric: the rising level phase is short, and
the drop in level is slower. Because of their suddenness and violence, these flash floods represent a major natural and recurrent risk for the touristic valley.
For the last decades, several damaging floods in Morocco lead to develop a policy of management of the water resources in the country. Locally,
after the flash flood of the Ourika Valley of 1995, several structural and non stuctural actions were undertaken. To reduce the high vulnerability of the
Valley new equipments have been set up. A warning monitoring system is installed in the upper reaches of the valley, it can display an alert to the population
along the valley. Supporting walls and gabions reinforce the banks of the river. Works to widen some narrows of the river bed have regulated the
flow of the river. Concrete sills and gabions break the flow of the main tributaries. The efficiency of these engineering structures is presently evaluated.
In the centre of Morocco, the High Atlas mountain range represents the most important water storage for the neighbouring arid plains through liquid and solid precipitation. In this context, we evaluated the performance of the Snowmelt Runoff Model (SRM) on the five main tributary watersheds of the High Atlas range. Due to the very low density of climate stations in the High Atlas, snowfall and snowmelt processes are difficult to monitor using meteorological data alone. In order to compensate for the lack of in situ data, snow maps are also derived from remotely-sensed data. We compared the streamflow forecasting performance when the model is driven by one or the other estimate of snow-covered area. Both estimates are generally comparable in all watersheds, and satisfactory streamflow simulations were obtained at seasonal time scales using both snow-cover products. However, significant differences can be observed for selected storms, with more accurate streamflow predictions being obtained when the remotely-sensed data are used.
Snow in the High Atlas Mountains is a major source for freshwater renewal and for water availability in the semi-arid lowlands of south-eastern Morocco. Snowfall- and snow-ablation monitoring and modelling is important for estimating potential water delivery from the mountain water towers to the forelands. This study is part of GLOWA-IMPETUS, an integrated management project dealing with scarce water resources in West Africa. The Ameskar study area is located to the south of the High Atlas Mountains, in their rain shadow. As a part of the M'Goun river basin within the upper Drâa valley, the study area is characterised by high radiation inputs, low atmospheric humidity and long periods with sub-zero temperatures. Its altitude ranges between 2000 m and 4000 m, with dominant north- and south-facing slopes. Snowfall occurs mainly from November to April but even summit regions can become repeatedly devoid of snow cover. Snow cover maps for the M'Goun basin (1240 km2) are derived from calculations of NDSI (Normalized Difference Snow Index) from MODIS satellite images and snow depth is monitored at four automatic weather stations between 2000?4000 m. Snowfall events are infrequent at lower altitudes. The presence of snow penitentes at altitudes above 3000 m indicates that snow sublimation is an important component of snow ablation. Snow ablation was modelled with the UEB Utah Energy Balance Model (Tarboton and Luce, 1996). This single layer, physically-based, point energy and mass balance model is driven by meteorological variables recorded at the automatic weather stations at Tounza (2960 m) and Tichki (3260 m). Data from snow pillows at Tounza and Tichki are used to validate the model's physical performance in terms of energy and water balances for a sequence of two snowfall events in the winter of 2003/4. First UEB modelling results show good overall performance and timing of snowmelt and sublimation compared to field investigations. Up to 44% of snow ablation is attributed to snow sublimation in typical winters with subzero temperatures and low atmospheric humidity at an altitude of 3000 m. At altitudes below 3000 m snowmelt generally dominates over sublimation. Unfortunately, the highest altitude zones suffer long periods with direct water loss into the atmosphere by sublimation in the course of which they cannot contribute to direct runoff or groundwater formation in the southern High Atlas Mountains.
Keywords: sublimation, snow ablation modelling, energy balance model, High Atlas Mountains
The paper evaluates long-term seasonal variations of the deuterium excess (d-excess = delta(2)H - 8. delta(18)O) in precipitation of stations located north and south of the main ridge of the Austrian Alps. It demonstrates that sub-cloud evaporation during precipitation and continental moisture recycling are local, respectively, regional processes controlling these variations. In general, sub-cloud evaporation decreases and moisture recycling increases the d-excess. Therefore, evaluation of d-excess variations in terms of moisture recycling, the main aim of this paper, includes determination of the effect of sub-cloud evaporation. Since sub-cloud evaporation is governed by saturation deficit and distance between cloud base and the ground, its effect on the d-excess is expected to be lower at mountain than at lowland/valley stations. To determine quantitatively this difference, we examined long-term seasonal d-excess variations measured at three selected mountain and adjoining valley stations. The altitude differences between mountain and valley stations ranged from 470 to 1665 m. Adapting the 'falling water drop' model by Stewart [J. Geophys. Res., 80(9), 1133-1146 (1975).], we estimated that the long-term average of sub-cloud evaporation at the selected mountain stations (altitudes between about 1600 and 2250 m.a.s.l.) is less than 1 % of the precipitation and causes a decrease of the d-excess of less than 2 per thousand. For the selected valley stations, the corresponding evaporated fraction is at maximum 7 % and the difference in d-excess ranges up to 8 per thousand. The estimated d-excess differences have been used to correct the measured long-term d-excess values at the selected stations. Finally, the corresponding fraction of water vapour has been estimated that recycled by evaporation of surface water including soil water from the ground. For the two mountain stations Patscherkofel and Feuerkogel, which are located north of the main ridge of the Alps, the maximum seasonal change of the corrected d-excess (July/August) has been estimated to be between 5 and 6 per thousand, and the corresponding recycled fraction between 2.5-3 % of the local precipitation. It has been found that the estimated recycled fractions are in good agreement with values derived from other approaches.
The basin of Oum-Er-Rabiaa is part of the Middle Atlas, it constitutes an important water resource on the scale of Morocco. The hydrogeological system of the region is characterized by many springs, some of which have a high salinity rate spilling into Oum-Er-Rabiaa river. The present study aims to investigate: Firstly, the distribution of lineaments along the major shear corridors crossing the area as well as their hydrogeological importance, and secondly, to verify the influence of geological characteristics on the physicochemical properties of the studied water bodies. This study is based on a combined analysis through: Remote Sensing, Satellite Imagery, Geographic Information Systems (GIS), Field Studies and Geochemical Analysis. The results demonstrated that the lithological and structural characteristics of the geological formations, play a predominant role in the creation of this hydrogeological system, as well as, in the diversity of the physicochemical proprieties of water resources in the area, these geological formations are mainly composed by: Liassic limestone characterized by a circulation of fresh water (fresh springs), this Liassic limestone is put in contact with the Triassic saline clays through geological faults, which is in the origin of the creation of saline springs contaminating the upstream of the Oum-Er-Rabiaa river. In the light of the decisive results obtained a set of solutions have been proposed such as the diversion of saline springs, the purification in situ, and the development of a fish farming project. These solutions aim to guarantee a better quality of water resources of the area, to preserve agriculture and to valorize the saline water bodies with a sustainable development perspective.
The Souss-Massa plain, an important agriculture area of the Middle Western of Morocco, is a depression zone filled with Plio-Quaternary sediments which are overlying a complex multi-layered sedimentary basement. Over the last decades, population growth, agriculture development and recurrent droughts have been increasing the pressure on the aquifers of the region. The shallow aquifer is intensively exploited. About 94% of the water resources in the basin are used for agriculture. Groundwater levels show a general, continuous depletion. Chemical tracers indicate a progressive deterioration of groundwater quality in many areas with multiple sources of salinity. Another consequence of overexploitation and water use for agriculture is the increase of nitrate concentrations in groundwater.
This multiple isotope investigation (18O, 2H, 14C, 3H, noble gases) confirms that the aquifer is mainly recharged by waters derived from the High Atlas Mountains, where the precipitation rate is higher than in the study area. The spatial variations of stable and radioactive isotope concentrations indicate that active mixing of recently recharged and old groundwater within the aquifer system. The recent recharge is observed mainly along the Souss River and in the irrigated areas.
The evolution of the fluids can be observed on a locale scale in the 3He/4He ratios, which are largely controlled by the amount of 4He, indicating the addition of terrigenic He to groundwater and/or mixing processes. The finding of mantle helium signature in shallow aquifer generally supports the assumption of the deep, permeable faults in the area of the Souss depression (El Klea and Biougra faults).
This study indicates the extent of groundwater renewability and allows establishing a scientifically-based water management model for sustainable exploitation of water resources in the Souss-Massa basin.
Application of stable isotope methods to evaluate the contribution of different water sources to groundwater recharge relies on the knowledge about isotopic signatures of these sources. The data collected at study sites in the Canadian Prairies show that snowpack isotopic signatures exhibit a high spatial variability over a small scale (<100[U+202F]m) limiting the usefulness of point samples to estimate an average isotopic composition of snow over a large area. Isotopic signatures of snowmelt runoff can be different from those of pre-melt snowpack, further undermining the applicability of snow isotopic signature to characterisation of snowmelt-driven hydrological processes. Accounting for the actual signature of snowmelt runoff has strong effects on its perceived role in recharging groundwater. The data also show that diffuse and depression-focussed components of groundwater recharge have different isotopic signatures, where the latter closely resembles snowmelt runoff.
Understanding the main controls on stable isotope variations in precipitation is fundamental for the interpretation of the hydrological cycle. However, spatio-temporal variations in δ18Op are poorly known in Morocco. Herein, we explore the relative influence of meteorological variables, spatial and orographic (altitudinal) effects, atmospheric circulation and moisture sources on precipitation stable isotopes in Morocco. Precipitation events and two-years-long monthly records from 17 rain-gauge stations in Morocco are investigated and compared in this study to global gridded records of monthly and annual stable isotopes in precipitation. We highlight that the main spatial controls on precipitation stable isotopes are the topography and the distance from marine source. The most depleted mean annual isotopes are located in the High Atlas Mountains (δ18Op=-9.56‰ and δ2Hp=-59.3‰), while the most enriched isotope ratios exist in southwestern Morocco (δ18Op=-2.35‰ and δ2Hp=-7.47‰). The well-constrained relationship between δ18Op and altitude describes a gradient of 0.11 to 0.18‰ per 100 m. The seasonal variation is expressed by a general enrichment that reaches -4.8‰ during the dry season, related to the recycled vapor contained within the summer precipitation. Notwithstanding the scarcity of temperature and precipitation measurements, the amount effect is observed in multiple stations during several rain events and precipitation seems to have more influence on δ18Op than temperature. Backward moisture trajectories indicate a distinct depletion in δ18Op in extreme events originating from the Atlantic Ocean. The presence of a rain shadow effect is also revealed on the lee side of High Atlas Mountains, southeastern Morocco.
The contribution of snowmelt to groundwater recharge at four sites in the southwestern United States was evaluated using stable isotopes of O and H. Paired precipitation collectors were installed at the study sites; data show that (1) there is often a significant difference between the stable isotope composition of fresh snow and the bulk meltwater derived from it (this suggests that using the isotope composition of high-elevation springs as a proxy for precipitation may not be sound if snow is a recharge source) and (2) collector design can significantly influence the stable isotope composition of collected snow. Because the isotope composition of snow from a given location becomes heavier (i.e., more rain-like) with increased exposure, using bulk snowmelt compositions to calculate input to groundwater recharge results in significantly increased estimates of snowmelt contributions to recharge (compared to estimates derived from fresh snow signatures). Snowmelt provides at least 40–70% of groundwater recharge at the study sites, although only 25–50% of average annual precipitation falls as snow. On the basis of these results and presently accepted scenarios for alterations in precipitation in the western United States over the next 50 years (significantly decreased snowpack due to increased atmospheric CO2), investigations of how climate change may affect groundwater resources are needed. We also investigated the potential for snow/atmospheric water vapor isotope exchange to influence the isotope signature of snow (which has been a subject of debate); the results of a laboratory experiment suggest that it can drive significant shifts in the isotope signature of snow, even at temperatures below 0°C.
The Visean transgression is well known in the main part of northern Morocco, where it was synchronous with faulting. At that time the Khenifra area, divided into pre-Visean blocks, was covered with a shallow sea, making an opportunity for developing this transgression in stages. Here, the Visean overlies the pre-Visean terrains through a major unconformity during at least four transgressive phases: (1) V1: limestones, then flysch, onto an anchizonal Ordovician series (N of Ba Moussa); (2) V2a: carbonated platform onto anchizonal Devonian series (Assif bou Imezdaoun sedimentary klippes); (3) V2b−V3a: detrital platform onto an epizonal Cambro-Ordovician series (Jebel Hadid Horst); (4) V3b: detrital submergence, in places carbonated, along the sides of the horsts, where the transgression accompanied fault movements, an Fe metallogeny and a resedimentation phenomenon. The Devonian klippes could originate from the edges of the grabens during these movements.
The surface and crustal structure of the Atlas ranges of Morocco are described by a structural section from the foreland basin of the Rif to the Sahara craton. The Atlas ranges derive from inversion of Jurassic extensional or transtensional troughs during the Cenozoic, and they consist of dominantly thick-skinned thrusts and folds separated by tabular plateaux. Paleozoic basement is downwarped in synclinal areas up to 3 km below sea level, but is exposed at the surface in the peripheral plains, thus lying at a higher regional elevation than in much of the interior of the ranges. Synorogenic basins are poorly preserved. Based on the surface geology and available geophysical data, a reinterpretation of the crustal structure is proposed, in which the thrust system of the High Atlas is interpreted to cut into the lower crust and offset the Moho. The moderate amount of shortening along the transect (about 12%) contrasts with the elevated Atlas topography, which cannot be explained by crustal thickening alone. The presence of Cenozoic alkaline volcanics, widespread in the Middle Atlas, together with low seismic velocities suggest the existence of a thermally anomalous mantle contributing to uplift in the region.
Uranium and thorium contents as well as radon alpha-activities per unit volume were evaluated inside different water samples by using a method based on calculating the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) detection efficiencies for the emitted alpha-particles and measuring the resulting track density rates. The validity of the SSNTD technique utilized was checked by analysing uranyl nitrate (UO2(NO3)26H2O) standard solutions. A relationship between water radon concentration and water transmission of different water sources belonging to two regions of the Middle Atlas (Morocco) water reservoir was found. The influence of the water flow rate as well as the permeability and fracture system of the host rocks of the sources studied was investigated.
Etude de la contribution de la fonte des neiges aux eaux de surfaces et souterraines
- J Benlekbir
Hydrogeological characterization of the Upper Drâa Catchment: Morocco
- S Cappy
Cappy S (2006) Hydrogeological characterization of the Upper Drâa
Catchment: Morocco (Issue August)
Isotopic changes during snow metamorphism oD oD 3
- I Friedman
- C Benson
- Jim Gleason
- S G Survey
Friedman I, Benson C, Gleason JIM, Survey SG (1991) Isotopic
changes during snow metamorphism oD oD 3