Occurrence des sécheresses dans le bassin de la Medjerda (Tunisie)

La probabilité d'occurrence des sécheresses dans le bassin de la Medjerda (Tunisie) est calculée en se basant sur les totaux pluviométriques annuels de 35 postes sur une période de quarante ans. Les moments statistiques des volumes de déficits face à une demande en eau fixée sont estimés par la méthode des séries. Une fonction de répartition marginale des volumes de déficits est proposée, ainsi que des fonctions de répartition conditionnelles pour des durées sèches de un à six ans. Plusieurs lois de probabilité couramment utilisées en hydrologie sont étudiées. Des applications de ce modèle sont présentées.The probability of occurrence of drought in the Medjerda basin (Tunisia) is estimated using the stochastic process based on the measurement of total annual rainfalls taken in 35 stations over a period of 40 years.Marginal and conditional distributions of shortage volumes are analytically proposed at each location. Mean, standard deviation and skewness coefficients of shortage volumes are used for setting up a Person type III model. Then, similarly to I-D-F curves, drought duration curves are plotted within a given threshold. A general formulation of statistics of shortage volume population is given. It is expressed in terms of the position, the location and the scale parameters of the rainfall generator process, for a given threshold value. As an application, some useful distributions in hydrology are examined (Normal, Galton, Gamma, Weibull) and expected drought volumes are estimed.Model verification is performed using three stations of the basin for which the observed sample was extended to a period of 58 years. Comparison between observed and calculated statistics of shortage shows a good agreement. Expected shortage volumes are mapped using the average rainfall at each station as a threshold. A second threshold was based on an agricultural water demand. The corresponding water supply expected was mapped

Carbon dioxide emissions mitigation strategies’ performance

The climate change matter is due to Green House Gas Emissions produced essentially by CO2 emissions. To overcome this problem, decision markers developed several policies among them the adoption of energy efficient measures and the development of renewable energies. Using a panel data analysis, this paper tries to investigate the impact of adoption of such solutions on emissions levels for 161 countries during the period 1985-2014. Estimation results demonstrate that the magnitude of emissions reduction is more important for energy efficiency and that the role of renewable energy still insufficient yet. Furthermore, we proved that non-renewable energy, income per capita and population growth are destructive facts of environmental quality

Identification de zones pluviométriques homogènes d’un bassin versant à partir de l’information topographique

La recherche de zones pluviométriques homogènes sur la base des informations issues de la topographie consiste à subdiviser un bassin versant en zones climatiques homogènes. Ces régions sont identifiées en intégrant une information externe en bonne corrélation avec la pluviométrie, à savoir le relief. Le climat étant caractérisé par la moyenne et l’écart‑type des séries mensuelles pluviométriques, une relation entre ces statistiques et les variables explicatives reliées à la topographie est établie sous la forme d’une régression linéaire multiple. Ces variables constituent des attributs topographiques, qui servent de support à une classification du bassin versant en zones homogènes, pouvant être une étape préliminaire à un travail d’optimisation de réseaux pluviométriques.The identification of homogeneous rainfall zones, on the basis of topographic information, consists of subdividing the area of a watershed into homogeneous climate zones. These regions are identified by integrating external information that is well correlated with rainfall, namely the relief. The climate is characterized by the average and standard deviation of monthly rainfall. In the present study, a relationship between these statistics and explanatory variables linked to the topography, was modelled using multiple linear regression. These variables constitute topographic attributes that are adopted as support for the classification of watersheds into homogeneous zones and may be the preliminary step in the optimisation of rainfall networks

Prédétermination des débits maximaux de crue par simulation Monte-Carlo de la pluie nette

Une méthodologie a été proposée pour la prédétermination des débits à partir de la pluviométrie. Il s’agit d’associer, en entrée, les simulations Monte Carlo de hyétogrammes de pluie nette avec un modèle d’hydrogramme unitaire à base de géomorphologie pour obtenir des hydrogrammes simulés en sortie. À la fin des simulations, l’analyse statistique des sorties permet d’apprécier l’étendue de la variabilité de la réponse du bassin aux événements pluvieux et de caractériser les débits et les temps de pointe. Un total de 44 simulations ont été menées pour chacun des 15 événements observés pour un petit bassin versant situé en Tunisie centrale. L’analyse des hydrogrammes générés a montré une assez faible dispersion des débits de pointe, d’une simulation à l’autre, pour un événement donné, et a mis en évidence la dissymétrie des distributions des débits et temps de pointe. L’exploitation des résultats de l’ensemble des simulations permet de dégager des relations empiriques caractérisant le comportement du bassin selon les débits de pointe, les temps de pointe, les temps de base et les volumes écoulés.The predetermination of peak discharges and flood volumes of ungauged basins is an important aspect of the management of surface waters, protection against floods, water supply, etc. In this study, a method is proposed for the predetermination of discharges from rainfall data. The method associates effective rainfall obtained from Monte Carlo Simulations (MCS) with a unit hydrograph based on geomorphology. The unit hydrograph (UH) based on geomorphology is selected knowing that the parameters can be obtained from topographic charts, soil charts and ground occupation charts, as well as from soil data. The UH used was produced from the Nash cascade model in which the scale and shape parameters were taken from the literature. These parameters depend on the hydrographical network, the Horton ratios and the average peak flow velocity, which is assumed to be constant throughout the network and with respect to time. The average peak flow velocity can be expressed as a function of 1) geomorphologic parameters such as the total surface area of the basin, the slope of the highest order stream, the Manning-Strickler coefficient, the width of the channel, the kinematic wave parameter of the highest order stream and the length of the main channel, and 2) the effective rainfall intensity and duration.With respect to effective rainfall intensities, the idea is to consider the effective rainfall as a vector of the parameters of the hydrological model, and then to use the MCS method to generate the corresponding components. The proposed simulation framework includes: 1) the specification of the data for which the geomorphologic parameters and the time increments are fixed for all simulations, whereas the duration of the total rainfall and the effective rainfall volume vary from one event to another, and constitute constraints determining whether or not simulations should be rejected, 2) the random drawing of effective rainfall intensities and durations, 3) the computation of resulting hydrographs and 4) the analysis of the simulated hydrographs, where the hydrographs are first simulated for each event and then simulated in their entirety to highlight indicators to characterize outputs.In order to statistically interpret the simulated hydrographs, the generated peak discharges were classified for each event, and their 25th, 50th and 75th percentiles were analyzed. The same treatment was applied to the simulated times to attain peak values. The use of the 25th and 75th percentiles makes it possible to evaluate the extent of the 50% interval of the simulated discharges, whereas the median and the mode make it possible to position values representative of the distribution of the generated discharges. The hydrographs are assumed have the same “recurrence” as their peak discharge. Hydrograph generation by the MCS method is a two step process: 1) the generation of effective rainfall intensities based on the assumption that the total volume is observed, and 2) the convolution of the unit hydrograph resulting from each interval of effective rainfall.The study site, Saddine1, is a small catchment with a surface area of 384 hectares. It is located adjacent to Makthar in Tunisia (northern latitude 35°48’06’’ and longitude 9°04’ 09’’) in a mountainous zone. The catchment is controlled by a small headwater dam and was monitored from 1992 to 1999. Observed over periods of five minutes, the maximum rainfall intensity was 324 mm/h and the minimal intensity was 10 mm/h. The maximum total rainfall recorded for an event was of 106 mm. The longest duration for an event was of approximately 5 hours (299 min) and shortest was 12 minutes. A great disparity in the volumes was also noted: the maximum volume observed was 67,200 m3 whereas the minimum was 1,275 m3. The peak discharges of the recorded hydrographs were very variable with a minimum/maximum ratio of about 1/1370. Indeed the maximum discharge observed was 85.6 m3/s, and the minimum discharge only 0.062 m3/s. The time to attain peak flows for the rainfall events varied from 10 to 120 minutes. The effective rainfall intensities were calculated using the infiltration index method, ϕ, which remains a method still largely used in spite of its rudimentary character. The effective rainfalls estimated for each event varied from 0.3 mm with 17.5 mm.Before using the MCS, the model was calibrated. The results of the calibration analysis showed that the calculated hydrographs were reasonable comparable to the observed hydrographs. In addition to the shape, the peak discharge and the peak time reconstitutions were satisfactory. A total of 44 simulations were carried out for each of the 15 events observed, of which 13 allowed for the identification of the distributions of effective rainfall intensities and durations. The remaining two events were used for the validation of the approach. The analysis of the generated hydrographs showed a rather weak dispersion of the peak output from one simulation to another, for a given event. Moreover, the discharges and times to attain peak discharge resulting from the generated hydrographs followed a dissymmetrical distribution. The observed values of the peak discharges and times to attain peak discharge represent realisations of output simulations with different probabilities of occurrence. In order to capitalize on the model, relationships between simulated peak discharges, times to peak discharge, base times and volumes were constructed

Modélisation pluie-débit et classification hydroclimatique

La recherche de similarité hydrologique est très importante pour l’estimation des débits aux bassins non jaugés. L’indice radiatif d’aridité, proposé dans le modèle de bilan hydrique de Budyko, en combinaison avec le bilan radiatif, représente un paramètre de contrôle de l’ETR (évapotranspiration réelle). Cet indice permet de définir des régions climatiques ou géobotaniques dans lesquelles s’inscrivent les modèles pluie-débit ajustés d’après des historiques d’observations hydroclimatiques. Le présent travail utilise le modèle HBV muni d’une routine d’optimisation à l’aide de l’algorithme SCE‑UA. Il propose une méthodologie de calage dans laquelle on tient explicitement compte de l’ETR établie à grande échelle, à partir de l’indice d’aridité. Cette méthode de calage adopte comme fonction objective la combinaison de trois critères : minimisation de l’écart quadratique sur les débits, minimisation de l’écart sur le bilan hydrique, minimisation de l’écart à l’ETR régionale. On montre qu’ainsi, on améliore la performance du modèle en période de validation.The research of hydrological similarity is very important for runoff estimation with respect to ungauged basins. The Budyko radiative dryness index may represent a control parameter for the estimation of actual evapotranspiration ETR, as output of rainfall-ruonff models. These models are generally adjusted according to hydro – climatic observations, whithout taking account for energy balance insights. Budyko index helps defining climatic or geobotanic regions, in which rainfall-runoff models may be enrolled. To develop these ideas, the HBV rainfall-runoff model is adopted, coupled to a SCE-UA optimisation tool. It is proposed to perform the model adjustment taking explicitly account for ETR regional estimation, as a constraint. The calibration method adopts an objective function combining three criteria: minimization of runoff root mean square error, minimization of water budget simulation error, minimization of the difference between mean annual simulated ETR and regional ETR. It is found that, by this way, model performances are enhanced, especially for the validation period

History of the Human and Nature Relationship, Discovery of Greenhouse Effect and Awareness of the Environmental Problem

The evolution of man and nature relationship during human history has allowed human beings to be sheltered from the threats of their natural environments and has permitted them to exercise their powers there but has against part the breakdown of this relationship because of the excessive exploitation of natural resources, discharges and waste that cause nature pollution. This rupture caused climate change due to the evolution of the production model from the primitive model to the capitalist model. The objective of this paper is to shed light on the evolution of the relationship between human beings and their natural environment and the awareness of the climate change problem. This research allows appreciating and comparing the effectiveness of the resolutions that can help researchers understanding the climate change context, serve as a springboard for empirical studies, and represent a decision tool for policymakers. To this end, we use a knowledge synthesis methodology to make an inventory of our research problem