Trends in frequency of precipitation extremes in the Yangtze River basin,China: 1960–2003 / Tendances d'évolution de la fréquence des précipitations extrêmes entre 1960 et 2003 dans le bassin versant du Fleuve Yangtze (Chine)

Abstract

The spatial distribution and trends in the frequency of precipitation extremes over the last 44 years (1960–2003), especially since 1990, have been analysed using daily precipitation data from 147 stations in the Yangtze River basin. The research results are as follows: (1) The 15 mm precipitation isohyet approximately divides the precipitation extremes (corresponding to the 95th percentile) of the stations in the middle and lower Yangtze reaches (higher) from those of the upper Yangtze reaches (lower). Also the starting time of the precipitation extremes in the middle and lower Yangtze reaches is earlier than of those in the upper Yangtze reaches. Precipitation extremes are concentrated mostly in June in the middle and lower Yangtze reaches, and July in the upper Yangtze reaches. (2) During the period 1960–2003, the first two decades had fewer precipitation extremes than the last two decades. There have been significant increasing trends and step changes in frequency of annual total precipitation extremes and precipitation extremes with a 1–5 day gap in the middle and lower Yangtze reaches. Precipitation extremes occur more frequently in shorter periods, separated by a few days. Precipitation extremes are also becoming more concentrated in the month with the highest frequency of extremes (June) in the middle and lower Yangtze reaches. In the upper Yangtze reaches, there is an upward tendency of extreme events in June. Increasing precipitation extremes in June for both the middle and lower, and the upper Yangtze reaches will increase the probability of flooding if the observed trends of the last 40 years continue into the future.     

Application du réseau des neurones artificiels à la prévision des débits horaires: Cas du bassin versant de l’Eure,France

RÉSUMÉ

Les modèles pluie–débit sont fortement utilisés dans la gestion des risques hydrologiques et la prévision des crues. Dans cette étude, nous présentons un modèle pluie–débit pour la prévision des débits horaires basé sur la technique des réseaux de neurones artificiels (RNA). Ce modèle a été développé et appliqué sur le bassin versant de l’Eure au Nord-Ouest de la France afin de dépasser les problèmes dus à la non-linéarité de la relation pluie–débit et à l’imprécision des données collectées. La création de ce modèle a nécessité plusieurs étapes pendant lesquelles nous avons pu déterminer les paramètres du modèle permettant la compréhension de la complexité hydrologique et la production des informations nécessaires à la prévision. Elles ont abouti à un modèle de réseau de neurones artificiels capable d’effectuer, en quelques secondes, des prévisions des crues efficaces jusqu’à un horizon de prévision de 48 h. Ces résultats confirment que les modèles RNA peuvent jouer un rôle important dans le domaine de la prévision car capables de modéliser la non-linéarité des relations pluie–débit rencontrées sur certains bassins hydrologiques.

Editor Z.W. Kundzewicz Associate editor E. Gargouri     

Application of linear and nonlinear techniques in river flow forecasting in the Kilombero River basin,Tanzania / Application de techniques linéaires et non-linéaires à la prévision des débits dans le bassin de la Rivière Kilombero,en Tanzanie

Abstract

Modelling of the rainfall–runoff transformation process and routing of river flows in the Kilombero River basin and its five sub-catchments within the Rufiji River basin in Tanzania was undertaken using three system (black-box) models—a simple linear model, a linear perturbation model and a linear varying gain factor model—in their linear transfer function forms. A lumped conceptual model—the soil moisture accounting and routing model—was also applied to the sub-catchments and the basin. The HEC-HMS model, which is a distributed model, was applied only to the entire Kilombero River basin. River discharge, rainfall and potential evaporation data were used as inputs to the appropriate models and it was observed that sometimes the system models performed better than complex hydrological models, especially in large catchments, illustrating the usefulness of using simple black-box models in datascarce situations.     

Analyse du transport solide en suspension dans le bassin versant de l'Oued El Hammam (Algérie du Nord)

Résumé

Dans les régions semi-arides et arides, caractérisées par des précipitations relativement faibles et souvent à caractère torrentiel, les facteurs climatiques jouent un rôle primordial dans l'érosion des sols à l'échelle des versants. La majeure partie de l'exportation des matériaux solides est effectuée par les cours d'eau lors des crues. La présente étude traite de l'évaluation et de la quantification du transport solide dans le bassin versant de l'Oued El Hammam, un sous-bassin important de la Macta caractérisé par une forte érosion hydrique. La sensibilité des roches à l'érosion, l'intensité des précipitations et les perturbations du régime d'écoulement font que le flux des matières en suspension (MES) transportées par l'Oued El Hammam atteint des valeurs très importantes. L'analyse du bilan qui règle le processus pluie–ruissellement–transport solide montre de bonnes relations, notamment entre la lame d'eau écoulée et la quantité de charge solide transportée. Nous présentons des modèles statistiques permettant de reproduire les flux de MES. Après calage et validation des modèles sur les chroniques mesurées, ils sont utilisés afin de reconstituer des chroniques de flux de MES non mesurées, à partir de données historiques de débit et de pluie. L'étude de la relation C–Q à l'échelle de la crue a été modélisée par une fonction puissance Y = aX^b ; une analyse statistique de la constante a et de l'exposant b a été menée afin d'expliquer le comportement de ces deux paramètres et de mieux comprendre l'aspect aussi bien pratique que théorique des processus.

Citation El Mahi, A., Meddi, M., et Bravard, J.-P., 2012. Analyse du transport solide en suspension dans le bassin versant de l'Oued El Hammam (Algérie du Nord). Hydrological Sciences Journal, 57 (8), 1642–1661.     

Seasonal and annual maximum streamflow forecasting using climate information: application to the Three Gorges Dam in the Yangtze River basin,China / Prévision d'écoulements saisonnier et maximum annuel à l'aide d'informations climatiques: application au Barrage des Trois Gorges dans le bassin du Fleuve Yangtze,Chine

Abstract

This paper explores the potential for seasonal prediction of hydrological variables that are potentially useful for reservoir operation of the Three Gorges Dam, China. The seasonal flow of the primary inflow season and the peak annual flow are investigated at Yichang hydrological station, a proxy for inflows to the Three Gorges Dam. Building on literature and diagnostic results, a prediction model is constructed using sea-surface temperatures and upland snow cover available one season ahead of the prediction period. A hierarchical Bayesian approach is used to estimate uncertainty in the parameters of the prediction model and to propagate these uncertainties to the predictand. The results show skill for both the seasonal flow and the peak annual flow. The peak annual flow model is then used to estimate a design flood (50-year flood or 2% exceedence probability) on a year-to-year basis. The results demonstrate the inter-annual variability in flood risk. The predictability of both the seasonal total inflow and the peak annual flow (or a design flood volume) offers potential for adaptive management of the Three Gorges Dam reservoir through modification of the operating policy in accordance with the year-to-year changes in these variables.     

Dynamique et modélisation des crues dans le bassin du Mono à Nangbéto (Togo/Bénin)

Résumé

Les inondations des dernières années en Afrique de l’Ouest rendent nécessaire la prévision hydrologique pour réduire la vulnérabilité des populations. Nous avons étudié la dynamique des crues dans le bassin du Mono en amont du barrage de Nangbéto (Togo et Bénin) par des méthodes statistiques et déterministes. L’augmentation des précipitations au cours de la décennie 1990 et la mise en eau du barrage de Nangbéto en 1988 ont modifié le régime du Mono, dont les débits d’étiages ont augmenté. Les débits entrants et sortants du barrage sont équivalents, même lors des crues. Les maximums annuels des débits entrants peuvent être modélisés par une distribution des valeurs extrêmes (GEV) de type Fréchet, tandis que ceux des débits sortants, suivent une loi GEV de type Weibull (bornée). Le mécanisme dominant de génération des crues dans le bassin est la montée progressive des eaux associée à l’augmentation de la saturation des sols. L’analyse des débits de crue entre 1988 et 2010 n’a pas montré d’augmentation de la magnitude ou de la fréquence des crues. Le modèle GR4J reproduit bien les débits de crues en période calage, mais ces critères de performance se dégradent lorsque l’on s’en éloigne. Dans ces conditions, l’utilisation de ce modèle pour évaluer les risques futurs de crues serait hasardeuse et il est nécessaire d’envisager d’autres types d’approches.     

Variabilité et tendances observées sur les débits moyens mensuels,saisonniers et annuels dans le bassin de la Falémé (Sénégal)

Le changement climatique, lié au réchauffement de la Terre, agit directement sur notre milieu naturel en le transformant et s’accompagne de modifications dans le cycle hydrologique. Il s’en suit une baisse drastique des ressources en eau disponibles du fait de la forte diminution des totaux pluviométriques reçus. Dans cette étude, nous utilisons le test de Mann-Kendall pour caractériser la variabilité et les tendances des débits dans le bassin de la Falémé sur la période 1954–2014. Les résultats de l’analyse révèlent une tendance à la baisse statistiquement significative sur pratiquement tous les mois et sur les périodes de hautes et de basses eaux. Une tendance a été observée aussi sur les années de faible hydraulicité durant lesquelles l’écoulement des périodes de hautes et basses eaux est moins important. Le test de Mann-Kendall s’est donc avéré efficace pour indiquer les tendances négatives de l’écoulement dans le bassin de la Falémé.     

Periodicity of sediment load and runoff in the Yangtze River basin and possible impacts of climatic changes and human activities / Périodicité de la charge sédimentaire et de l'écoulement dans le bassin du Fleuve Yangtze et impacts possibles des changements climatiques et des activités humaines

Abstract

Periodicity of the runoff and the sediment load, and possible impacts from human activities and climatic changes, in the Yangtze River basin during 1963–2004 are discussed based on the monthly sediment and runoff data, and using the wavelet approach. Research results indicated that: (a) Sediment load changes are severely impacted by the different types of human activity (e.g. construction of water reservoirs, deforestation/afforestation); and the runoff variability is the direct result of climatic changes, e.g. the precipitation changes. (b) The impacts of human activity and climatic changes on the sediment load and runoff changes are greater in smaller river basins (e.g. the Jialingjiang River basin) than in larger river basins. The response of sediment load and runoff changes to the impacts of human activities and climatic changes are prompt and prominent in the Jialingjiang River basin relative to those in the mainstem of the Yangtze River basin. (c) Construction of the Three Gorges Dam has already had obvious impacts on the sediment transport process in the middle and lower Yangtze River basin, but shows no obvious influence on the runoff changes. Construction of the Three Gorges Dam will result in further re-adjustment of the scouring/filling process within the river channel in the middle and lower Yangtze River basin, and have corresponding effects on the altered sediment load because of the Dam's operation for the river channel, ecology, sustainable social economy and even the development of the Yangtze Delta. This will be of concern to local governments and policy makers.     

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.     

Analyse statistique des séquences sèches dans un bassin du nord de la Tunisie / Statistical analysis of dry events in a northern Tunisian basin

Abstract

A comparative statistical study of dry events during the rainy season is presented. In particular, we carried out statistical processing of the daily records of raingauges in the downstream basin of Lake Ichkeul, in the north of Tunisia. The climate is characterized by a rainy season lasting from the autumn until spring. The Poisson distribution was applied to describe the number of rainfall events, and negative binomial distribution was applied for the length of the dry events, in the rainy season. Since rainfall events are shorter, their duration follows a geometrical distribution, as theoretically required. For planning purposes, the longest seasonal dry spells associated with the various statistical recurrence periods are derived on the basis of the fitted GEV functions. A hydrological year starts at the beginning of the first rainfall event of a given season. The length of hydrological year is determined by the time interval between the start dates of two subsequent rainy seasons. The beginning of the hydrological year occurs on average toward mid-September, but the probability of it occurring before 15 September exceeds 40%. Spatial analysis of dry events is also done. A significant fraction of the dry events occurred for at least two stations simultaneously. Furthermore, 4.5% of the dry events have been observed at all three stations. The analysis of the dry events gives an alternative method to examine the dry spell phenomenon.     

Calcul des pluies et débits classés sur le bassin du Bani (Mali): une approche de la vulnérabilité des ouvrages et de la population depuis la sécheresse

Résumé Dans un contexte de changement climatique, les dimensionnements d'ouvrages hydrauliques peuvent avoir un rôle crucial dans une évaluation de la vulnérabilité. Ainsi, on calcule avec les données les plus récentes possibles la pluie journalière maximale annuelle de période de retour donnée (10, 20 et 100 ans) sur 51 stations ainsi que les débits de projet pour six stations sur le bassin versant du Bani au Mali (129 000 km²). Pluies et débits sont calculés avec une méthode utilisant les L-moments et en découpant le bassin en régions climatiques homogènes. Une formule empirique d'évaluation du débit décennal est enfin réévaluée, considérant la baisse importante des débits maximaux depuis 1970. Les valeurs trouvées soulignent l'importance du choix de la période, puisque quelques années peuvent faire varier de façon importante les valeurs classées.     

Trends in annual discharge from the Yangtze River to the sea (1865–2004) / Tendances et épisodes extrêmes dans les débits annuels du Fleuve Yangtze débouchant dans la mer (1865–2004)

Abstract

Uninterrupted records of annual discharge from the Yangtze River to the sea (at Datong Hydrographical Station) began in the 1950s. This series shows no significant trend. However, at Hankou, a station upstream from Datong, annual discharges have been observed since 1865 almost without gaps. The annual discharges at Datong and Hankou were found to be closely correlated. Based on the regression equation, the missing annual discharges at Datong were estimated and a time series from 1865 to 2004 was established. Although the annual discharge has varied greatly, it shows a significant decreasing trend. The trendline revealed an 8.2% decrease from 1865 to 2004. The decrease in discharge was attributed to increases in water consumption and reservoir construction, while the interannual variations were related to climate variability. The decreasing trend in discharge is expected to continue in the coming decades due to human activities. This decreasing trend should be taken into account in the decision making on the South-to-North-Water Diversion projects.     

Spatial distribution of resistivity in the hydrogeological systems,and identification of the catchment area in the Rharb basin,Morocco / Répartition spatiale de la résistivité dans les systèmes hydrogéologiques et détection des zones de captages dans le bassin du Rharb,Maroc

Abstract

Abstract Geophysical results obtained in the Rharb basin, Morocco are reported. Correlations between hydrogeological well logs reveal several water-bearing Plio-Quaternary units resting on a substrate of blue marls. Geo-electrical borehole analyses were interpreted using bi-logarithmic diagrams which indicate the permeable layers of the aquifer and also its basement. Resistivity data from NE–SW and NW–SE electrical sections allow definition of the permeable/impermeable levels, and identification of ?ditches? that may be favourable sectors for hydrogeological exploitation. Resistivity anomalies were investigated by analysing maps of resistivity at 400 and 1000 m AB. Anomalies identified in the Rharb basin are related to the thickening of the permeable bodies (sand, limestone, sandstone deposits). In the coastal zone (AB = 1000 m), there is a strong decrease of the resistivity gradient (35–10 Ω m), which is probably linked to marine intrusion. Electrical anomalies allow detection of the water-bearing zones notably in the western and southwestern parts of the Rharb basin.     

Prediction of base flows from basin characteristics: a case study from Zimbabwe / Prévision de débits de base à partir de caractéristiques du bassin: une étude de cas au Zimbabwe

Abstract

Abstract Base flows make up the flows of most rivers in Zimbabwe during the dry season. Prediction of base flows from basin characteristics is necessary for water resources planning of ungauged basins. Linear regression and artificial neural networks were used to predict the base flow index (BFI) from basin characteristics for 52 basins in Zimbabwe. Base flow index was positively related to mean annual precipitation (r = 0.71), basin slope (r = 0.76), and drainage density (r = 0.29), and negatively related to mean annual evapotranspiration (r = –0.74), and proportion of a basin with grasslands and wooded grasslands (r = –0.53). Differences in lithology did not significantly affect BFI. Linear regression and artificial neural networks were both suitable for predicting BFI values. The predicted BFI was used in turn to derive flow duration curves of the 52 basins and with R ² being 0.89–0.99.     

Effects of suburban construction on runoff contributing zones in a small southern Ontario drainage basin / Les conséquences du développement suburbain pour les zones d'appel dans un petit bassin versant de sud Ontario

Abstract

The runoff response of a small drainage basin in southern Ontario has been monitored over a 5 year period, during which 25 per cent of its surface has been modified by suburban construction activity. Direct runoff response to summer and autumn rainstorms has not been noticeably affected by the development, but response to spring snowmelt has increased by three to four times. Summer and autumn storm runoff still appears to be generated mainly by direct precipitation on a natural, saturated, contributing zone alongside the channel, which has been little affected by the construction activity. The construction surfaces have had their infiltration capacities greatly reduced by devegetation and compaction, but runoff from them does not contribute to the storm hydrograph unless ephemeral channels and swales which link them to the main stream are saturated and capable of conducting flow. This happens rarely during rainstorms, but consistently during snowmelt, when ground conditions are extremely wet. The seasonal contrasts in the effect of partial suburban development on direct runoff response, are therefore caused by seasonal variations in the extent to which the construction surfaces are integrated into the active runoff contributing zone of the drainage basin.     

Runoff reduction by forest growth in Hiji River basin,Japan / Diminution de l'écoulement causée par la croissance forestière dans le bassin versant du Fleuve Hiji,Japon

Abstract

Forest growth unfavourably reduces low flows and annual runoff in a basin in Japan. Annual precipitation and runoff of the watershed are summarized from observed daily rainfall and discharge, and annual evapotranspiration is estimated from the annual water balance. The water balance analysis shows obvious trends: reduced annual runoff and increased evapotranspiration over a 36-year period when forest growth increased the leaf area index. Between two periods, 1960–1969 and 1983–1992, mean annual runoff decreased 11%, from 1258 to 1118 mm, due to a 37% increase in evapotranspiration (precipitation minus runoff) from 464 to 637 mm. This increase in evapotranspiration cannot be attributed to changed evaporative demand, based on climatic variability over the 36-year period of record. Flow duration curves show reduced flows in response to forest growth. In particular, they suggest stronger absolute changes for higher flows but stronger proportional changes for medium and lower flows. A distributed model is applied to simulate the influences of five scenarios based on a 30% change in leaf area index and 5% change in soil storage capacity. From the simulation results, canopy growth appears to contribute much more to flow reduction than changes in soil storage capacity.     

SIMULATION OF A SERIES OF DAILY AREAL MEAN RAINFALLS FOR A BASIN USING RAINFALL OBSERVATIONS AT A REFERENCE STATION LOCATED OUTSIDE THE BASIN / Simulation d'une série de précipitations journalières moyennes spatiales sur un bassin,en utilisant les hauteurs pluviométriques observées à une station de référence située en dehors du bassin

Abstract

A mathematical model is built which enables daily estimates to be made of the areal mean rainfalls for a basin using rainfall observations at a reference station of the same climature* but which may be situated at some distance from the basin. The method consists of:

1. (1) determining the probabilities of the characteristic types of association between areal mean rainfalls of varying magnitude at the basin and rainfall events of various types at the reference station.

2. (2) establishing the conditional distributions of areal mean rainfalls at the basin.

3. (3) estimating the areal mean rainfalls at the basin (a) by the Monte Carlo method and (b) by accepting that the mean basin rainfalls and the reference station rainfall are, in their respective statistical distributions, fractiles of the same order.

Finally, the validity of the simulated series is checked by means of various tests.     

Uncertainty and sensitivity analysis of runoff and sediment yield in a small agricultural watershed with KINEROS2 / Analyse d'incertitude et de sensibilité des simulations d'écoulement et de transport solide de KINEROS2 dans un petit bassin versant agricole

Abstract

Using the Monte Carlo (MC) method, this paper derives arithmetic and geometric means and associated variances of the net capillary drive parameter, G, that appears in the Parlange infiltration model, as a function of soil texture and antecedent soil moisture content. Approximate expressions for the arithmetic and geometric statistics of G are also obtained, which compare favourably with MC generated ones. This paper also applies the MC method to evaluate parameter sensitivity and predictive uncertainty of the distributed runoff and erosion model KINEROS2 in a small experimental watershed. The MC simulations of flow and sediment related variables show that those parameters which impart the greatest uncertainty to KINEROS2 model outputs are not necessarily the most sensitive ones. Soil hydraulic conductivity and wetting front net capillary drive, followed by initial effective relative saturation, dominated uncertainties of flow and sediment discharge model outputs at the watershed outlet. Model predictive uncertainty measured by the coefficient of variation decreased with rainfall intensity, thus implying improved model reliability for larger rainfall events. The antecedent relative saturation was the most sensitive parameter in all but the peak arrival times, followed by the overland plane roughness coefficient. Among the sediment related parameters, the median particle size and hydraulic erosion parameters dominated sediment model output uncertainty and sensitivity. Effect of rain splash erosion coefficient was negligible. Comparison of medians from MC simulations and simulations by direct substitution of average parameters with observed flow rates and sediment discharges indicates that KINEROS2 can be applied to ungauged watersheds and still produce runoff and sediment yield predictions within order of magnitude of accuracy.     

Long-range forecasts of River Po discharges based on predictable solar activity and a fuzzy neural network model / Prévisions à long terme des débits du Fleuve Pô basées sur l’activité solaire prévisible et sur un modèle de réseau de neurones flou

Abstract

Abstract Is it possible to make seasonal and interannual forecasts of hydrological variables if one cannot predict next week’s rainfall? Contrary to common view, some scientists support the hypothesis that variations in mean global temperature and precipitation are controlled more by external forcing (solar variability and volcanic eruptions) than by increasing atmospheric concentration of greenhouse gases. Temperature and precipitation are connected with special phases of the 11-year sunspot cycle, which coincide with significant accumulation of energetic solar eruptions. Because of the possibility of identifying years with many solar eruptions, the attractive prospect emerges of the long-term hydrological forecasting based on cycles of solar activity. Starting from this assumption, an expert system was built based on a fuzzy neural network model for seasonal and interannual forecasting of the Po River discharge. It was found that indices of solar activity and of global circulation are sufficient to yield useful forecasts of hydrological variables.