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Mahe G.,Mohammed V University | Lienou G.,University of Yaounde I | Bamba F.,University of Sfax | Paturel J.E.,CNRS HydroSciences Montpellier Laboratory | And 6 more authors.
IAHS-AISH Publication | Year: 2011

The Niger River basin covers 1.2 million km2 and extends over nine countries in West Africa. Its average discharge to the sea is about 6000 m3 s-1. The main upstream flood is produced during the 6-7 months of the tropical rainy season. The hydrological regime has been modified due to climatic and anthropogenic changes. There are only a few major dams on the River Niger, and future development plans will modify its regime and the flooded areas. The goal of this study is to provide a comprehensive overview of the hydrological changes of the Niger regime in its different sub-basins, in order to assess the impacts of future changes. The time series at Koulikoro and for the upstream basins show a high interannual flow variability since 1907, and a strong decrease since 1970. The runoff deficit in the Bani River after 1970 is greater than the rainfall deficit, due to a decrease in the groundwater level. NOAA images for 1990-2000 indicate that the flooded surfaces have decreased in the Inner Delta. The Sahelian flood from rivers in Burkina-Faso and Niger, and from the Sokoto River in Nigeria, has increased due to land degradation, despite the reduced rainfall. Now, more than half of the water of the Lower Niger comes from the Benue River. For the Sahelian basins, the increase in runoff can be closely related to the deforestation, but the dramatic decrease of the groundwater levels seems to be related to climate change. In the future, large changes will come from the proposed dams, which will reduce the flood peaks and the flooded surface areas, but will also have positive effects on the management of water resources. © 2011 IAHS Press.

Ducrocq V.,Meteo - France | Braud I.,IRSTEA | Davolio S.,CNR Institute of Neuroscience | Ferretti R.,University of L'Aquila | And 48 more authors.
Bulletin of the American Meteorological Society | Year: 2014

The establishment of a cold pool can maintain intense convective systems far upstream from the mountain barrier. For instance, the unusual location of the HPE over the Gard plain in September 2002 was explained by the presence of a low-level cold pool induced by the convective system itself. These lifting mechanisms were further studied by examining how characteristics of a conditionally unstable flow impinging upon the coastal complex terrain of the northwestern Mediterranean influence the location and intensity of quasi-stationary MCSs. A dedicated field campaign was thus designed to improve the present state of knowledge of Mediterranean HPEs and flash-flooding events and to improve numerical models. The Hpiconet rain supersite, located in the eastern extremity of the northern east west transect, aimed at characterizing the very finescale variability of the surface rainfall with one rain gauge or disdrometer per 4 km2.

Mulligan M.,King's College London | Cruz L.L.S.,King's College London | Pena-Arancibia J.,King's College London | Pandey B.,King's College London | And 2 more authors.
Water International | Year: 2011

This paper analyses water availability and use within and between the Challenge Program on Water and Food basins. It describes the main features of water demand and supply in the basins and indicates where there are deficits and opportunities for development of water resources. A typology of basin water resources status uses a range of global spatial datasets. The main outcomes of basin activities on water availability are identified. Interbasin assessment of water availability is very challenging for such very large basins, due in large part to difficulties in collecting and integrating local data sets. © 2011 International Water Resources Association.

Fabre J.,French National Center for Scientific Research | Collet L.,CNRS HydroSciences Montpellier Laboratory | Milano M.,CNRS HydroSciences Montpellier Laboratory | Ruelland D.,French National Center for Scientific Research | And 3 more authors.
IAHS-AISH Proceedings and Reports | Year: 2014

This study aims at defining the main stakes in the development of a generic, multidisciplinary approach to evaluate water supply capacity and its spatial and temporal variability over long time periods. A common modelling framework was applied over two Mediterranean basins with different physical and anthropogenic characteristics: the Ebro (85 000 km2, Spain) and the Herault (2500 km2, France) catchments. Runoff and river flow regulations were simulated using conceptual hydrological models and reservoir management models, respectively. Water demand was estimated from population and unit water consumption data for the domestic sector, and from irrigated area, crop, soil and climatic data for the agricultural sector. A ratio comparing water resource availability to water demand was computed on each catchment. Working on two catchments with different geographical scales and water management issues underlines the challenges in the development of a reliable and generic water allocation assessment method. © Copyright 2014 IAHS Press.

Boyer J.F.,IRD Montpellier | Servat E.,IRD Montpellier | Casiot C.,French National Center for Scientific Research | Jourde H.,CNRS HydroSciences Montpellier Laboratory
IAHS-AISH Proceedings and Reports | Year: 2014

According to the missions of the French OSUs (Observatoires des Sciences de l'Univers), an observatory must provide, on a given territory, a permanent monitoring activity. This mission requires strict organization linked to a relevant monitoring network, a high level of data quality and data availability. The requirements are provided by an Environmental Information System (EIS) such as those implemented for two Observation Systems which are part of OREME OSU: one dedicated to hydro-biogeochemical processes concerning metals and metalloids in surface waters downstream from the Carnoules mine, the other, dedicated to Multi Scale Observatory of flood dynamics and hydrodynamics in Karst. A specific architecture was chosen to develop an EIS that identifies and provides information mainly around three functions: (i) data centralization in a client/server database following the standards for metadata description, (ii) safe management of scientific information, and (iii) a geo-referenced photo album representing territory, measurement stations, and instrumentation devices used. © Copyright 2014 IAHS Press.

Ruelland D.,French National Center for Scientific Research | Hublart P.,CNRS HydroSciences Montpellier Laboratory | Tramblay Y.,IRD Montpellier
IAHS-AISH Proceedings and Reports | Year: 2015

This paper investigates the uncertainties linked to climate change impacts on runoff in four mesoscale basins (900 to 1800 km2) in the Mediterranean region. Runoff simulations were based on a daily conceptual model including a snow module. The model was calibrated and validated according to a differential split-sample test over a 20-year period and four competing criterions aiming to represent model structural uncertainty based on the concept of Pareto optimality. Five regional climate models (RCMs) from the Med-CORDEX initiative were used to provide temperature and precipitation projections under RCP8.5 by 2050. The RCMs' inability to realistically simulate reference climate (notably precipitation) led us to apply a monthly perturbation method in order to produce a range of climate scenarios. The structural uncertainty bounds obtained from the hydrological simulations over the reference period showed that the model was able to correctly reproduce observed runoff despite contrasted hydrological conditions in (and in between) the basins. Climate projections were shown to be convergent regarding temperatures, which could increase by about +1 to 3 °C on each basin. In contrast, no clear trends in precipitation could be put in evidence, some RCMs leading to a mean annual precipitation decrease (up to 64%), and others to an increase (up to 33 %). The hydrological projections resulted from the combination of the hydrological simulation bounds with the range of climate projections. Despite the propagation of those uncertainties, the 2050 hydrological scenarios agreed on a significant runoff decrease (2-77 %) during spring on all basins. On the opposite, no clear trend in runoff could be observed for the other seasons. © Author(s) 2015.

Filahi S.,Direction de la Meteorologie Nationale | Filahi S.,Hassan II University | Tanarhte M.,Max Planck Institute for Chemistry | Tanarhte M.,Hassan II University | And 3 more authors.
Theoretical and Applied Climatology | Year: 2015

The purpose of this paper is to provide a summary of Morocco’s climate extreme trends during the last four decades. Indices were computed based on a daily temperature and precipitation using a consistent approach recommended by the ETCCDI. Trends in these indices were calculated at 20 stations from 1970 to 2012. Twelve indices were considered to detect trends in temperature. A large number of stations have significant trends and confirm an increase in temperature, showing increased warming during spring and summer seasons. The results also show a decrease in the number of cold days and nights and an increase in the number of warm days and nights. Increasing trends have also been found in the absolute warmest and coldest temperatures of the year. A clear increase is detected for warm nights and diurnal temperature range. Eight indices for precipitation were also analyzed, but the trends for these precipitation indices are much less significant than for temperature indices and show more mixed spatial patterns of change. Heavy precipitation events do not exhibit significant trends except at a few locations, in the north and central parts of Morocco, with a general tendency towards drier conditions. The correlation between these climate indices and the large-scale atmospheric circulations indices such as the NAO, MO, and WEMO were also analyzed. Results show a stronger relationship with these climatic indices for the precipitation indices compared to the temperature indices. The correlations are more significant in the Atlantic regions, but they remain moderate at the whole country scale. © 2015 Springer-Verlag Wien

Marchand P.,CNRS HydroSciences Montpellier Laboratory | Salles C.,CNRS HydroSciences Montpellier Laboratory | Rodier C.,CNRS HydroSciences Montpellier Laboratory | Hernandez F.,CNRS HydroSciences Montpellier Laboratory | And 2 more authors.
Houille Blanche | Year: 2014

Intermittent rivers pose different challenges to stream rating due to high spatial and temporal gradients. Long dry periods, cut by short duration flush flood events explain the difficulty to obtain reliable discharge data, for low flows as well as for floods: problems occur with standard gauging, zero flow period, etc. Our study aims to test the use of an acoustic Doppler current meter (ADC) for improving stream rating curves in small catchments subject to large variations of discharge, solid transport and high eutrophisation levels. The study is conducted at the outlet of the river Vène, a small coastal river (67 km2) located close to the city of Montpellier (France). The low flow period lasts for more than 6 month; during this period the river flow is sustained by effluents from urban sewage systems, which allows development of algae and macrophytes in the riverbed. The ADC device (Sontek ®Argonaut SW) is a pulsed Doppler current profiling system designed for measuring water velocity profiles and levels that are used to compute volumetric flow rates. It is designed for shallow waters (less than 4 meter depth). Its main advantages are its low cost and high accuracy (1% of the measured velocity or 0.05 m/sec, as reported by the manufacturer). The study evaluate the improvement in rating curves in an intermittent flow context and the effect of differences in sensitivity between low and high water level, by comparing mean flow velocity obtained by ADC to direct discharges measurements. The study also report long-term use of ADC device, by considering effects of biofilms, algae and macrophytes, as well as solid transport on the accuracy of the measurements. In conclusion, we show that the equipment is reliable and is able to provide additional information. However we show also that it is always difficult to measure low flow. © 2014 Société Hydrotechnique de France.

Neppel L.,CNRS HydroSciences Montpellier Laboratory | Arnaud P.,IRSTEA | Borchi F.,CNRS HydroSciences Montpellier Laboratory | Carreau J.,CNRS HydroSciences Montpellier Laboratory | And 6 more authors.
Houille Blanche | Year: 2014

This paper focuses on a comparison of 3 families of extreme rainfall frequency analysis methods: 1) purely local approaches which consist in fitting a probability distribution function (pdf) to a sample of observed daily rainfall, 2) local-regional approaches where the sample of annual maxima daily rainfall at the target site is enlarged by rainfall observations in a surrounding homogeneous neighbourhood and 3) purely regional approaches for estimating the extreme rainfall pdf at an ungaged site. For 2) and 3) the extreme rainfall pdf can be estimated either by frequency analysis based on the extreme value theory or from the simulations of the French stochastical rainfall model named SHYREG. The comparison relies on a dataset of 1568 daily rainfall gages belonging to the French Weather Service (Météo-France) or the French Electricity Company (EDF) in the southern half of France. A comparison methodology and several comparison criteria have been defined to evaluate the bias and variances of the quantiles and the confidence intervals. The main results are: 1) At the local scale, the General Pareto Distribution fitted on a peak over threshold sample performs better that the Generalized Extreme Value pdf fitted on max annual sample, 2) the exponential pdf is clearly unsuitable in Mediterranean area, 3 the local approaches perform poorly compared to the local-regional and purely regional frequency analyses except for the MEWP weather pattern frequency analysis which is comparable to the local regional frequency analysis for non-Mediterranean climate and when the calibration sample size exceeds 10 years, 4) the local regional frequency analysis and the SHYREG method performances are comparable, and 5) there is only a weak decrease in performances when using a purely regional frequency analysis instead of a local-regional frequency analysis. © 2014 Société Hydrotechnique de France.

Soubeyroux J.-M.,Meteo - France | Neppel L.,CNRS HydroSciences Montpellier Laboratory | Veysseire J.-M.,Meteo - France | Tramblay Y.,CNRS HydroSciences Montpellier Laboratory | And 2 more authors.
Houille Blanche | Year: 2015

This paper focuses a synthesis of the works led within the framework of the French project ANR/Extraflo on the evolution of the daily (and infra daily) extreme rainfall in France. An important dataset of more than 900 series was used. It was shown that a majority of series presented a not significant upward trend in particular in Mediterranean area, in relation with various recent exceptional extreme events. An interesting way to characterize this evolution consists in identifying climatic co-variables associated to heavy rainfall events (weather patterns, average temperatures, flow of humidity) and in taking into account them with a non stationary POT model. The application of this method with climatic projections under scenario A2 from IPCC could lead to a possible increase on extreme precipitation quantiles on the horizon 2070. © Société Hydrotechnique de France, 2015.

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