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

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

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight NCD Risk Factor Collaboration (NCD-RisC)

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions

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

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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Evaluation of the GPM-IMERG Precipitation Product for Flood Modeling in a Semi-Arid Mountainous Basin in Morocco

International audienceA new precipitation dataset is provided since 2014 by the Global Precipitation Measurement (GPM) satellite constellation measurements combined in the Integrated Multi-satellite Retrievals for GPM (IMERG) algorithm. This recent GPM-IMERG dataset provides potentially useful precipitation data for regions with a low density of rain gauges. The main objective of this study is to evaluate the accuracy of the near real-time product (IMERG-E) compared to observed rainfall and its suitability for hydrological modeling over a mountainous watershed in Morocco, the Ghdat located upstream the city of Marrakech. Several statistical indices have been computed and a hydrological model has been driven with IMERG-E rainfall to estimate its suitability to simulate floods during the period from 2011 to 2018. The following results were obtained: (1) Compared to the rain gauge data, satellite precipitation data overestimates rainfall amounts with a relative bias of +35.61% (2) In terms of the precipitation detection capability, the IMERG-E performs better at reproducing the different precipitation statistics at the catchment scale, rather than at the pixel scale (3) The flood events can be simulated with the hydrological model using both the observed and the IMERG-E satellite precipitation data with a Nash–Sutcliffe efficiency coefficient of 0.58 and 0.71, respectively. The results of this study indicate that the GPM-IMERG-E precipitation estimates can be used for flood modeling in semi-arid regions such as Morocco and provide a valuable alternative to ground-based precipitation measurements