Flood Hazard Mapping Using Two Digital Elevation Models: Application in a Semi-Arid Environment of Morocco

The High Atlas of Morocco is a semi-arid mountainous environment that frequently suffers from natural hazards. For example, the watersheds upstream of Marrakech city are subject to extreme floods, caused by heavy rains. These episodes are frequent and often devastating, as was the August 1995 event that caused hundreds of deaths in the Ourika Valley. The purpose of this work is to characterize the risk of flooding in this valley, by simulating the water levels and the floodplain extension. This watershed of the Ourika is characterized by a high relief, a rugged topography and a low permeability substratum. To perform this hydraulic simulation, the resolution and accuracy of Digital Elevation Models (DEM) can strongly impact the results in terms of water levels and flow velocities during floods. Two digital elevation models (DEM) were compared: a DEM ASTER with a spatial resolution of 30 m and a DEM derived from stereoscopic images of Pleiades with a resolution of 4 m. Using a hydraulic model (HEC-RAS) and the two DEM resolutions, flood areas corresponding to different return periods are simulated and compared. For the assessment of the two DEM, many areas are selected that are characterized by different types of exposure: highly frequented tourist areas near a regional road and agricultural areas on alluvial terraces, where cultivated fields and infrastructure are vulnerable. The results showed that the high-resolution Pleiades DEM allows for accurate mapping of floodplains in complex terrain, as it realistically representsthe topography and allows correct simulation of observed water levels. This study highlights the added value of a high-resolution remote sensing for flood modeling in areas where data are scarce

LES CRUES DE L’OUED ISSIL EN AMONT DE MARRAKECH (MAROC), UN RISQUE NATUREL RECURRENT THE FLOODS OF THE WADI ISSIL UPSTREAM OF MARRAKESH (MOROCCO), A RECURRING NATURAL HAZARD

The wadi Issil originates in the High Atlas of Marrakesh, at altitudes above 2000 m. The mountainous part of the watershed is characterized by significant slopes, a low-permeable bedrock and a widespread dense hydrographic network.Concerning precipitation, the upstream stations of the basin record heavy and high rainfall levels. The average value e.g. in Agaiouar is approximately 582 mm a year, which is close to what can be found in sub-humid lands.This hydrogeomorphic and rainfall situation is conducive to the development of sudden and very fast floods. The recently opened hydrometric station of Aït Bouzguia has recorded some floods over the last years with a fast rising time (from 1h15 to 1h30). Using the data recording at the station of Ouagjdite, located upstream of the basin, response times of 2h30 were collected. These short periods pose a major risk as they do not allow a prediction of such floods in due time.These types of flood are renown for their infrastructure damages in Marrakesh, especially in areas near the wadi Issil. They often lead to substantial costs and sometimes the loss of human lives. Wadi’s overflow phenomenon is also exacerbated by numerous rubble or household waste, being abandoned on the stream bed. These waste materials shrink the wadi’s section and reduce its conveyance accordingly. Furthermore, the reduced diameter of some waste water systems, notably bridges nozzles, increases the risk.Several land-use plannings have been submitted, some others have been applied and some are currently underway. They roughly consist in dredging and raising banks of some sections, and in building new bridges and protective reinforcement walls along the wadi’s shores. These actions should strengthen with the strict prohibition of waste and rubble disposal in the stream bed. This can be done by promoting awareness of people living close to the wadi and an overall improvement of the environment involved. Aside from that, there could be a broader and fruitful coordination between the Wilaya, the water administration, the municipalities and Civil Society

Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories: a pooled analysis of 2181 population-based studies with 65 million participants

Summary Background Comparable global data on health and nutrition of school-aged children and adolescents are scarce. We aimed to estimate age trajectories and time trends in mean height and mean body-mass index (BMI), which measures weight gain beyond what is expected from height gain, for school-aged children and adolescents. Methods For this pooled analysis, we used a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. We applied a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5–19 years. The model allowed for non-linear changes over time in mean height and mean BMI and for non-linear changes with age of children and adolescents, including periods of rapid growth during adolescence. Findings We pooled data from 2181 population-based studies, with measurements of height and weight in 65 million participants in 200 countries and territories. In 2019, we estimated a difference of 20 cm or higher in mean height of 19-year-old adolescents between countries with the tallest populations (the Netherlands, Montenegro, Estonia, and Bosnia and Herzegovina for boys; and the Netherlands, Montenegro, Denmark, and Iceland for girls) and those with the shortest populations (Timor-Leste, Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala, Bangladesh, Nepal, and Timor-Leste for girls). In the same year, the difference between the highest mean BMI (in Pacific island countries, Kuwait, Bahrain, The Bahamas, Chile, the USA, and New Zealand for both boys and girls and in South Africa for girls) and lowest mean BMI (in India, Bangladesh, Timor-Leste, Ethiopia, and Chad for boys and girls; and in Japan and Romania for girls) was approximately 9–10 kg/m2. In some countries, children aged 5 years started with healthier height or BMI than the global median and, in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall (eg, boys in Austria and Barbados, and girls in Belgium and Puerto Rico) or gaining too much weight for their height (eg, girls and boys in Kuwait, Bahrain, Fiji, Jamaica, and Mexico; and girls in South Africa and New Zealand). In other countries, growing children overtook the height of their comparators (eg, Latvia, Czech Republic, Morocco, and Iran) or curbed their weight gain (eg, Italy, France, and Croatia) in late childhood and adolescence. When changes in both height and BMI were considered, girls in South Korea, Vietnam, Saudi Arabia, Turkey, and some central Asian countries (eg, Armenia and Azerbaijan), and boys in central and western Europe (eg, Portugal, Denmark, Poland, and Montenegro) had the healthiest changes in anthropometric status over the past 3·5 decades because, compared with children and adolescents in other countries, they had a much larger gain in height than they did in BMI. The unhealthiest changes—gaining too little height, too much weight for their height compared with children in other countries, or both—occurred in many countries in sub-Saharan Africa, New Zealand, and the USA for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls. Interpretation The height and BMI trajectories over age and time of school-aged children and adolescents are highly variable across countries, which indicates heterogeneous nutritional quality and lifelong health advantages and risks

Rising rural body-mass index is the main driver of the global obesity epidemic in adults

Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities(.)(1,2) This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity(3-6). Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017-and more than 80% in some low- and middle-income regions-was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing-and in some countries reversal-of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.Peer reviewe

Comparison of flood modeling approaches in semiarid Mountainous catchments (High-Atlas, Morocco)

International audienceIn semi-arid regions such as the Mediterranean basin, floods usually represent a largecontribution to water resources. In addition, climate scenarios indicate a possible increase in extremeevents in the Mediterranean region. Therefore, it is necessary to model floods to better understand theprocesses involved and predict these risks. The Moroccan catchments flowing downstream of theHigh-Atlas Mountains are among the areas most vulnerable to flooding. The Issyl catchment (170km²)is located at the foothills of the High Atlas Mountains, with altitudes ranging from 632 to 2295m, andproducing floods that directly affect the city of Marrakech. The Rheraya catchment is a mountainousbasin with altitudes ranging from 1000m to 4165m, and affected by violent floods that constitute athreat for the villages located in low elevation areas. This paper compares the efficiency of two modelstructures, based either on the Soil Conservation Service - Curve Number (SCS-CN) method or theGreen and Ampt model. In addition, the comparison is also performed using global and semidistributed model structures to account for the spatial variability of rainfall. A total of 21 flood eventsthat occurred between 2008 and 2014 were tested for the two watersheds. The results of the globalapproach show a good reproduction of the maximum discharge with both models, but the flood volumeare not adequately reproduced for the Rheraya catchment. The results of the semi-distributedapproach show a clear improvement for several events, with better Nash criterion values on averagewith the SCS-CN model. In conclusion, we found that the Green and Ampt model outperforms theSCS-CN model in global mode, and it is the opposite in semi-distributed mode. Since the parametersof the Green-Ampt model can be successfully approximated using soil information, this model appearsadequate for climate changes studies or real time flood forecasting

Apport de modélisation hydraulique à la cartographie des zones inondables. Cas du bassin versant de la Gheraya (Haut Atlas, Maroc)

International audienceLes oueds du Haut Atlas de Marrakech ont la triste réputation d’être imprévisibles et redoutables parleurs crues éclairs et leurs inondations répétées des dernières décennies (1989, 1995, 1999, 2006,2009, 2014). Le bassin versant de la Gheraya (225 km²) ne sort pas de la règle. Ses fortes cruespeuvent inonder des zones agricoles, des zones de fréquentation touristique et les voies decommunication. A cet effet, ce travail consiste à caractériser l’aléa de crue en simulant les hauteursdes eaux de l’oued et les extensions latérales des crues. Après une analyse fréquentielle des débitsde pointe, et à l’aide d’un modèle numérique de terrain (MNT) à bonne résolution (4 mètres) et desoutils de modélisation hydraulique, nous avons simulé l’étendue des crues de différentes périodes deretour sur les berges de l’oued. Le choix des secteurs d’application est motivé par deux types d’enjeu: une zone touristique habituellement fréquentée par les visiteurs (Rha de Moulay Brahim) où sontexposés des bâtiments de restauration, la route régionale 203 et évidemment les vies humaines. Laseconde zone est un secteur d’activité agricole sur les terrasses alluviales au niveau de la ville deTahannaout où les champs et quelques aménagements anthropiques sont vulnérables. Lacartographie des zones inondables attire l’attention sur le risque des débordements de la Gherayasur ces zones d’activités humaines ; notamment par l’inondabilité des champs cultivés, de certainsbâtiments et de la route qui désenclave la haute vallée d’Imlil et d’Asni

A spatial and integrated flood risk diagnosis

International audiencePurpose-The purpose of this paper is to identify vulnerable areas for flood hazard and to analyze stakes exposed in touristic valley of Morrocan mountains. The three goals are: methodological (low-cost diagnosis without starting data), operational (to show the risk and identify avenues of prevention in Ourika) and incentive (to reproduce this on other sectors in Morocco). Design/methodology/approach-The vulnerability of three areas of the Ourika valley (the most frequented) was assessed by a hydro-geomorphological study, human frequentation surveys and risk indices at the building scale. Findings-Surveys carried out in the field allowed the identification of areas with high risk, the evaluation of the buildings' vulnerability and the frequentation of the valley. Evacuation plans, allowing easy access to potential refuges in case of flood, were finally proposed. Originality/value-The reproducible, inexpensive and relevant nature of the approach (integrated and spatialized) helps in decision making and facilitating dialogue for prevention

Analysis of observed climate trends and high resolution scenarios for the 21st century in Morocco

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Validation of the AROME, ALADIN and WRF Meteorological Models for Flood Forecasting in Morocco

International audienceFlash floods are common in small Mediterranean watersheds and the alerts provided by real-time monitoring systems provide too short anticipation times to warn the population. In this context, there is a strong need to develop flood forecasting systems in particular for developing countries such as Morocco where floods have severe socio-economic impacts. In this study, the AROME (Application of Research to Operations at Mesoscale), ALADIN (Aire Limited Dynamic Adaptation International Development) and WRF (Weather Research and Forecasting) meteorological models are evaluated to forecast flood events in the Rheraya and Ourika basin located in the High-Atlas Mountains of Morocco. The model evaluation is performed by comparing for a set of flood events the observed and simulated probabilities of exceedances for different precipitation thresholds. In addition, two different flood forecasting approaches are compared: the first one relies on the coupling of meteorological forecasts with a hydrological model and the second one is a based on a linear relationship between event rainfall, antecedent soil moisture and runoff. Three different soil moisture products (in-situ measurements, European Space Agency’s Climate Change Initiative ESA-CCI remote sensing data and ERA5 reanalysis) are compared to estimate the initial soil moisture conditions before flood events for both methods. Results showed that the WRF and AROME models better simulate precipitation amounts compared to ALADIN, indicating the added value of convection-permitting models. The regression-based flood forecasting method outperforms the hydrological model-based approach, and the maximum discharge is better reproduced when using the WRF forecasts in combination with ERA5. These results provide insights to implement robust flood forecasting approaches in the context of data scarcity that could be valuable for developing countries such as Morocco and other North African countries

Comparison of modeling approaches for flood forecasting in the High Atlas Mountains of Morocco

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