Hydrological assessment of different satellite precipitation products in semi-arid basins in Morocco

In data-sparse regions and in developing countries such as Morocco, where flooding has serious socio-economic impacts, satellite-based precipitation products open new possibilities for monitoring and modelling water resources and floods. The objective of the study is to explore the possibility of using satellite precipitation products (SPPs) with hydrological models (CREST and MISDc) over 9 basins in Morocco. This work provides a hydrological assessment of three SPPs that have demonstrated good capabilities in reproducing precipitation over different basins in Morocco (GPM IMERG – PERSIANN CDR (PERCDR) and CHIRPS). The two hydrological models are coupled with a stochastic calibration method to provide the different ranges of uncertainties. In addition, we investigate the ability of SPPs on reproducing the November 2014 flood event that affected a large part of Morocco. The results indicated that, in calibration, both hydrological models provided similar performance to reproduce river discharge with observed precipitation or PERSIANN CDR. In validation, the combination of the MISDc model with PERSIANN CDR performed the best, notably allowing a good simulation of the flood hydrographs during the November 2014 event. Future analysis of relationships between SPPs, basin properties, and hydrological modelling technique will allow to find the appropriate combination for different application purposes

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 Summary Analysis of Groundwater Vulnerability to Climate Variability and Anthropic Activities in the Haouz Region, Morocco

The Haouz aquifer is undergoing climatic aridity and anthropic pressure largely related to the agricultural sector. In this study, special attention was given to the main factors that have a direct impact on the fluctuations of the piezometric level (PL). Different statistical analyses (cross-correlations, PCA, cascading analysis) of the relationship between these factors were applied here. The results identify three distinct groundwater operating systems. The first is manifested in areas dominated by groundwater irrigation. The correlation is insignificant between the PL and surface water (R ≤ ±0.3). The natural balance of the water cycle is then disturbed causing a pronounced deficit in the PL. The second system is perceptible in areas dominated by irrigation from surface water, while the third system is noticeable in Bour areas, cultivated in rainfed mode. For both systems, the hydrological cycle is preserved, and the contribution of surface water to groundwater recharge is noticeable (±0.4 ≤ R ≤ ±1). Drought transfer between the water cycle components occurs in a cascading process for both systems. These results can help decision-makers to identify the risks related to groundwater vulnerability to climatic variability and overexploitation in the Haouz region, allowing for the promotion of efficient groundwater management

Comparison of High-Resolution Satellite Precipitation Products in Sub-Saharan Morocco

Precipitation is a crucial source of data in hydrological applications for water resources management. However, several regions suffer from limited data from a ground measurement network. Remotely sensed data may provide a viable alternative for these regions. This study aimed to evaluate six satellite products (GPM-F, CHIRPS, PERSIANN-CCS-CDR, GPM-L, GPM-E and PDIR-Now), with high spatio-temporal resolution, in the sub-Saharan regions of Morocco. Precipitation observation data from 33 rain-gauge stations were collected and used over the period from September 2000 to August 2020. The assessment was performed on three temporal scales (daily, monthly and annually) and two spatial scales (pixel and basin scales), using different quantitative and qualitative statistical indices. The results showed that the GPM-F product performed the best, according to the different evaluation metrics, up to events with 40 mm/day, while the GPM near real-time products (GPM-E and GPM-L) were better at detecting more intense rainfall events. At the daily time scale, GPM-E and GPM-L and, on monthly and annual scales, CHIRPS and PERSIANN-CCS-CDR, provided satisfactory precipitation estimates. Moreover, the altitude-based analysis revealed a bias increasing from low to high altitudes. The continental and mountainous basins showed the lowest performance compared to the other locations closer to the Atlantic Ocean. The evaluation based on the latitudes of rain gauges showed a decrease of bias towards the most arid zones. These results provide valuable information in a scarcely gauged and arid region, showing that GPM-F could be a valuable alternative to rain gauges

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

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Comparison of High-Resolution Satellite Precipitation Products in Sub-Saharan Morocco

Precipitation is a crucial source of data in hydrological applications for water resources management. However, several regions suffer from limited data from a ground measurement network. Remotely sensed data may provide a viable alternative for these regions. This study aimed to evaluate six satellite products (GPM-F, CHIRPS, PERSIANN-CCS-CDR, GPM-L, GPM-E and PDIR-Now), with high spatio-temporal resolution, in the sub-Saharan regions of Morocco. Precipitation observation data from 33 rain-gauge stations were collected and used over the period from September 2000 to August 2020. The assessment was performed on three temporal scales (daily, monthly and annually) and two spatial scales (pixel and basin scales), using different quantitative and qualitative statistical indices. The results showed that the GPM-F product performed the best, according to the different evaluation metrics, up to events with 40 mm/day, while the GPM near real-time products (GPM-E and GPM-L) were better at detecting more intense rainfall events. At the daily time scale, GPM-E and GPM-L and, on monthly and annual scales, CHIRPS and PERSIANN-CCS-CDR, provided satisfactory precipitation estimates. Moreover, the altitude-based analysis revealed a bias increasing from low to high altitudes. The continental and mountainous basins showed the lowest performance compared to the other locations closer to the Atlantic Ocean. The evaluation based on the latitudes of rain gauges showed a decrease of bias towards the most arid zones. These results provide valuable information in a scarcely gauged and arid region, showing that GPM-F could be a valuable alternative to rain gauges

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

Challenges in flood modeling over data-scarce regions: how to exploit globally available soil moisture products to estimate antecedent soil wetness conditions in Morocco

International audienceThe Mediterranean region is characterized by intense rainfall events giving rise to devastating floods. In Maghreb countries such as Morocco, there is a strong need for forecasting systems to reduce the impacts of floods

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

Evaluation of the Drivers Responsible for Flooding in Africa

Africa is severely affected by floods, with an increasing vulnerability to these events in the most recent decades. Our improved preparation against and response to this hazard would benefit from an enhanced understanding of the physical processes at play. Here, a database of 399 African stream gauges is used to analyze the seasonality of observed annual maximum flood, precipitation and soil moisture between 1981 and 2018. The database includes a total of 11,302 flood events, covering most African regions. The analysis is based on directional statistics to compare the annual maximum river flood with annual maximum rainfall and soil moisture. The results show that the annual maximum flood in most areas is more strongly linked to the annual peak of soil moisture than of annual maximum precipitation. In addition, the interannual variability of flood magnitudes is better explained by the variability of annual maximum soil moisture than by the variability in the annual maximum precipitation. These results have important implications for flood forecasting and the analysis of the long-term evolution of these hydrological hazards in relation with their drivers.Water Resource