Mohamed Meddi

Global rainfall erosivity assessment based on high-temporal resolution rainfall records

The exposure of the Earth’s surface to the energetic input of rainfall is one of the key factors controlling water erosion. While water erosion is identified as the most serious cause of soil degradation globally, global patterns of rainfall erosivity remain poorly quantified and estimates have large uncertainties. This hampers the implementation of effective soil degradation mitigation and restoration strategies. Quantifying rainfall erosivity is challenging as it requires high temporal resolution(<30 min) and high fidelity rainfall recordings. We present the results of an extensive global data collection effort whereby we estimated rainfall erosivity for 3,625 stations covering 63 countries. This first ever Global Rainfall Erosivity Database was used to develop a global erosivity map at 30 arc-seconds(~1 km) based on a Gaussian Process Regression(GPR). Globally, the mean rainfall erosivity was estimated to be 2,190 MJ mm ha−1 h−1 yr−1, with the highest values in South America and the Caribbean countries, Central east Africa and South east Asia. The lowest values are mainly found in Canada, the Russian Federation, Northern Europe, Northern Africa and the Middle East. The tropical climate zone has the highest mean rainfall erosivity followed by the temperate whereas the lowest mean was estimated in the cold climate zone.

Cartographie de l’érosion dans le bassin versant de l’Oued Mina en Algérie par télédétection et SIG

Résumé Dans cette étude, on a fait appel à la télédétection et aux systèmes d’information géographiques (SIG) pour évaluer et cartographier l’érosion hydrique en utilisant l’équation universelle des pertes en sol USLE dans le bassin versant de l’Oued Mina en Algérie. Ce bassin est caractérisé par une grande irrégularité dans les précipitations, une forte pente, une lithologie essentiellement marneuse et une couverture végétale très faible ce qui le rend très vulnérable à l’érosion. L’USLE est la combinaison de six facteurs spécifiques qui décrivent les caractéristiques du bassin versant. Les données de télédétection multi-temporelles et les SIG sont utilisés pour évaluer et cartographier chaque facteur individuellement. L’intégration des cartes thématiques des facteurs du modèle USLE dans le SIG permet de cerner l’impact de chaque facteur dans les pertes en sol, de classer par importance relative les zones d’érosion, et de quantifier les pertes en sol dans le bassin. Editeur Z.W. Kundzewicz Citation Toumi, S., Meddi, M., Mahé, G., et Brou, Y.T., 2013. Cartographie de l’érosion dans le bassin versant de l’Oued Mina en Algérie par télédétection et SIG. Hydrological Sciences Journal 58 (7), 1542–1558.

Hydrogeochemical assessment of the Upper Cheliff groundwater (North West Algeria)

The quality of the Upper Cheliff groundwater, located in North West Algeria, has in recent years undergone serious deterioration due to uncontrolled discharge of urban wastewaters, intensive use of chemical fertilizers in agriculture as well as to overexploitation. This study aims at analyzing the flow pattern of the Upper Cheliff groundwater, determining its current hydrochemical status and understanding the mineralization processes involved in its chemical quality. Two piezometric and sampling campaigns were carried out in 2008 in high water (April) and low water (October) periods. The major chemical ions (Ca2+, Mg2+, Na+, K+, Cl−, HCO3−, NO3−, SO42−) were analyzed in all samples. The piezometric data were mapped and allowed to analyze the groundwater flow conditions, in particular at the boundaries of the aquifer. The interpretation of hydrochemical data was made using various methods (Piper diagram, Stabler classification, base exchanges index, bi-elements scatter diagrams, saturation indices, mapping and multivariate principal component analysis). The results provide a better understanding of this aquifer hydrogeology and hydrochemistry. Several hydrochemical types (chloride-calcium, chloride-sodium and bicarbonate-calcium) characterize the groundwater. Mineralization processes and the origin of salinity are determined by the lithology of the aquifer (dissolution, base exchanges), and by climatic (evaporation) and anthropogenic factors (agricultural and urban wastes). The groundwater in the Upper Cheliff is currently of poor quality. This status is worrying, as this groundwater is an important natural resource for the socio-economic development of this region. Urgent measures must be taken to preserve this resource.

Artificial Neural Network Rainfall-Discharge Model Assessment Under Rating Curve Uncertainty and Monthly Discharge Volume Predictions

The accuracy of rainfall-discharge volume model predictions depends on the model design and uncertainty of the available stage-discharge measurements used to fit the rating curve, which converts a time-series of recorded stage into discharge. In general, the rating curve uncertainty is the product of several combined sources. Over Algerian rivers, the extrapolation of the rating curve beyond the gauging range is the main source of this uncertainty. This study, therefore, represents a quantitative approach to reflect rigorously the impact of the rating curve uncertainty on the improvement of monthly discharge volume prediction quality by the artificial neural network (ANN) rainfall-discharge model. The rating curve uncertainty of the Fer à cheval hydrometric station in the Mazafran watershed is performed within Bayesian analysis for stationary rating curves using the BaRatin method. This allows as to build a new time series of discharge in order to assess an ANN rainfall-discharge model. To do that, Levenberg–Marquardt back propagation neuronal network has been applied over 1972-2012 time-period, for five hydrometric stations in the Algiers Coastal Basin. The model inputs were constructed in different ways, during the algorithm development, such as precipitation, antecedent precipitation with different monthly lag times and antecedent monthly discharge volume. The results indicate that training/validation of ANN rainfall-discharge volume model is widely affected by the streamflow datasets uncertainty. A large proportion of model prediction errors are significantly improved when considering the rating curve uncertainty.

Regionalisation of rainfall erosivity in northern Algeria

The risk of erosion and desertification is a major problem in the Mediterranean region in general and Algeria in particular. Algeria has a known downward trend of very high rainfall since 1975, especially in the Central and Western regions. In this work, the spatial pattern and temporal trend of the modified Fournier index (MFI) are investigated. Also, it is aimed to answer the question of whether a change has occurred or not in the concentration of rainfall using the precipitation concentration index (PCI). A total of 117 rainfall stations are used to determine these two indices as well as the development of a formula for calculating MFI based on annual rainfall. For mapping the modified Fournier index, 273 stations are used. The results show no change in the seasonal distribution of rainfall. However, a downward trend of about 30% of MFI is present in the Central and Western regions. The eastern regions of the North Algeria have not experienced this decline. The spatial variability shows that the MFI value increases from the west to east and from the south to north.

Spatial and Time Variability of Drought Based on SPI and RDI with Various Time Scales

The spatial and temporal variability of droughts were studied for the Northeast Algeria using SPI and RDI computed with monthly precipitation data from 123 rainfall stations and CFSR reanalysis monthly temperature data covering the period 1979–80 to 2013–14. The gridded temperature data was interpolated to all the locations having precipitation data, thus providing to compute SPI and RDI with the time scales of 3-, 6- and 12-month with the same observed rainfall data. Spatial and temporal patterns of droughts were obtained using Principal Component Analysis in S-Mode with Varimax rotation applied to both SPI and RDI. For all time scales of both indices, two principal components were retained identifying two sub-regions that are similar and coherent for all SPI and RDI time scales. Both components explained more than 70% and 74% of drought spatial variability of SPI and RDI, respectively. The identified sub-regions are similar and coherent for all SPI and RDI time scales. The Modified Mann-Kendall test was used to assess trends of the RPC scores, which have shown non-significant trends for decreasing drought occurrence and severity in both identified drought sub-regions and all time scales. Both indices have shown a coherent and similar behavior, however with RDI likely showing to identify more severe and moderate droughts in the southern and more arid sub-region which may be due to its ability to consider influences of global warming. Results for RDI are quite uniform relative to time scales and show smaller differences among the various climates when compared with SPI. Further assessments covering the NW and NE of Algeria using longer time series should be performed to better understand the behavior of both indices.

Comparing SPI and RDI Applied at Local Scale as Influenced by Climate

Drought and wetness events were studied in the Northeast Algeria with SPI and RDI. The study area includes a variety of climatic conditions, ranging from humid in the North, close to the Mediterranean Sea, to arid in the South, near the Sahara Desert. SPI only uses precipitation data while RDI uses a ratio between precipitation and potential evapotranspiration (PET). The latter was computed with the Thornthwaite equation, thus using temperature data only. Monthly precipitation data were obtained from 123 rainfall stations and monthly temperature data were obtained from CFSR reanalysis gridded temperature data. Both data sets cover the period 1979–80 to 2013–14. Using ordinary kriging, the gridded temperature data was interpolated to all the locations having precipitation data, thus providing to compute SPI and RDI with the same observed rainfall data for the 3-, 6- and 12-month time scales. SPI and RDI were therefore compared at station level and results and have shown that both indices revealed more sensitive to drought when applied in the semi-arid and arid zones. Differently, more wetness events were detected by RDI in the more humid locations. Comparing both indices, they show a coherent and similar behavior, however RDI shows smaller differences among climate zones and time-scales, which is an advantage relative to the SPI and is likely due to including PET in RDI.

Modeling of discharge and sediment transport through the SWAT model in the basin of Harraza (Northwest of Algeria)

Abstract The objective of this study is to model discharge and solid erosion quantification through a small agricultural watershed by applying the SWAT model (Soil and Water Assessment Tools) on the Wadi Harraza’s basin of which is part of Wadi Cheliff’s basin, with an average altitude of 500 m, drains an area of 568 sq km. Soil and Water Assessment Tool (SWAT, version 2009) model integrated with Geographic Information System (ArcGIS, version 10.0) were used to simulate the discharge and sediment concentration of Wadi Harraza’s basin for the period from 2004 to 2009. Model calibration and validation were performed for monthly time periods using Sequential Uncertainty Fitting 2 (SUFI-2, version 2) within SWAT-CUP. Our calibration and validation outputs for monthly simulation showed a good model performance for discharges. Thus the evolution of the average total annual sediment in the Wadi Harraza’s basin which will be deposited in the Wadi Cheliff, is estimated at 54.24 t ha−1.

Correction to: Spatial and Time Variability of Drought Based on SPI and RDI with Various Time Scales

Due to an oversight, Figure 1 image and Figure 4 caption were incorrectly captured in the original publication.

Impact of Climate Variability on Hydrology of the Western Mitidja Watershed, Algeria

The objective of this study is to analyze the hydro-climatic regimes of the watershed of Mitidja West, and then try to evaluate the influence of climate on superficial flows. Rainfall data and databank for monthly discharges come from the National Agency of Hydraulic Resources (ANRH), rainfall are recorded from 23 rainfall stations distributed over the watershed and whose size varies from one station to another, and Time series of discharges data are generally from 1987 to 2012, but vary in duration. However, we noted that flows have been subjected to ruptures of 1975 until the middle of the 1980s. However, this reduction is due to a the climate impact associated with precipitation which decrease significantly since the end of the 75 years; or an anthropogenic impact due to the many hydraulic infrastructure development since 1985. Thus, for the simulation of the discharges from the rains, the efficiency of the model to simulate monthly discharges of the basin is given by the analysis of the criterion of Nash, of which it gave satisfactory values ​​superior to (60%), we can say, afterwards, that the GR2M model has a certain efficiency to simulate the discharges in the monthly time step and to guarantee a better understanding of the hydrological behavior of the basin.