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On met en évidence une fluctuation périodique du niveau du fleuve Sénégal à la station de Podor en période d'étiage, qui s'ajoute à l'évolution moyenne du niveau et se traduit par un réhaussement en début de journée à 8H et un abaissement en fin de journée à 18H. Ce signal périodique analyse de décembre à juin s'observe sur toute la période analysée (du 01/01/2000 au 11/03/2019). Son amplitude moyenne tend à augmenter avec le temps, en passant de 2 cm en 2000 à 4 cm en 2019. Ceci permet de penser que les fluctuations ont une origine anthropique, au moins partielle (prélèvements diurnes probablement). On met également en évidence une inversion de pente moyenne de ligne d’eau entre les stations de Podor et Richard Toll, intervenue de façon prolongée à deux reprises depuis janvier 2019 et qui perdure depuis le 18/02/2019. L'hypothèse la plus vraisemblable pour expliquer ce phénomène, compte tenu des niveaux observés à Podor, Richard Toll et Diama et des débits observés à Matam et Diama, correspond à une alimentation du fleuve par un reflux du lac de Guiers par le canal de la Tahouey. Une partie de cet apport pourrait alors remonter le fleuve à partir de Richard Toll, du fait des apports de l'amont très affaiblis par les prélèvements et l'évaporation entre Matam et Podor. Des mesures de débit sur le terrain seraient nécessaires pour expliquer l'origine des deux phénomènes de façon certaine.

Une analyse des pluies journalieres extremes du bassin du Cheliff (plus grand bassin du Nord de l’Algerie) a ete etablie sur la periode 1971–2010. Pour cela 13 stations pluviometriques ont ete selectionnees et recueillies aupres de l’Agence Nationale des Ressources hydrauliques (ANRH). Six indices de pluies journalieres ont ete analyses pour caracteriser l’evolution temporelle de la frequence et l’intensite des pluies journalieres sur la periode d’etude. Ces indices correspondent a la pluie totale annuelle des jours de pluies ( 1 mm), aux percentiles 90, 95, 99 et 99.5% et a l’intensite journaliere des jours de pluie (1 mm). Le test de Mann–Kendall indique une tendance generale a la baisse significative pour les pluies totales et l’intensite journaliere de certaines stations. La frequence des fortes pluies ne montre pas de changement significatif de son evolution temporelle pour la majorite des stations. La recherche de relation entre les indices de pluies journalieres et les differents modes de circulation atmospherique a mis en evidence l’influence de l’oscillation mediterraneenne sur la variabilite des precipitations journalieres du Cheliff, particulierement pour les stations qui ont connu une baisse significative de leur indice de pluies journalieres

This research investigated the effect of climate change on the two main river basins of Senegal in West Africa: the Senegal and Gambia River Basins. We used downscaled projected future rainfall and potential evapotranspiration based on projected temperature from six General Circulation Models (CanESM2, CNRM, CSIRO, HadGEM2-CC, HadGEM2-ES, and MIR005) and two scenarios (RCP4.5 and RCP8.5) to force the GR4J model. The GR4J model was calibrated and validated using observed daily rainfall, potential evapotranspiration from observed daily temperature, and streamflow data. For the cross-validation, two periods for each river basin were considered: 1961-1982 and 1983-2004 for the Senegal River Basin at Bafing Makana, and 1969-1985 and 1986-2000 for the Gambia River Basin at Mako. Model efficiency is evaluated using a multi-criteria function (F-agg) which aggregates Nash and Sutcliffe criteria, cumulative volume error, and mean volume error. Alternating periods of simulation for calibration and validation were used. This process allows us to choose the parameters that best reflect the rainfall-runoff relationship. Once the model was calibrated and validated, we simulated streamflow at Bafing Makana and Mako stations in the near future at a daily scale. The characteristic flow rates were calculated to evaluate their possible evolution under the projected climate scenarios at the 2050 horizon. For the near future (2050 horizon), compared to the 1971-2000 reference period, results showed that for both river basins, multi-model ensemble predicted a decrease of annual streamflow from 8% (Senegal River Basin) to 22% (Gambia River Basin) under the RCP4.5 scenario. Under the RCP8.5 scenario, the decrease is more pronounced: 16% (Senegal River Basin) and 26% (Gambia River Basin). The Gambia River Basin will be more affected by the climate change.

Study region : The study considers six precipitation stations located in Senegal, West Africa. Senegal is located in the Sahel, an area that is threatened by climate variability and change. Both droughts and extreme rainfall have been an issue in recent years. Study focus : Two different statistical downscaling techniques were applied to the outputs of four regional climate models at six selected precipitation stations in Senegal. First, the delta-change method was applied to the mean annual precipitation as well as the 5, 10, 20, 50 and 100-year return period daily precipitation events. Second, a quantile–quantile transformation (QQ) was used to downscale the monthly distributions of precipitation simulated by regional climate models (RCMs). The 5, 10, 20, 50 and 100-year daily precipitation events were afterward calculated. All extreme events were calculated assuming that maximum annual daily precipitations follow the generalized extreme value (GEV) distribution. The two-sided Kolmogorov–Smirnov (KS) test was finally used to assess the performance of the quantile–quantile transformation as well as the GEV distribution fit for the annual maximum daily precipitation. New hydrological insights for the region : Results show that the two downscaling techniques generally agree on the direction of the change when applied to the outputs of same RCM, but some cases lead to very different projections of the direction and magnitude of the change. Projected changes indicate adecline in mean precipitation except for one RCM over one region in Senegal. Projected changes in extreme precipitations are not consistent across stations and return periods. The choice of the downscaling technique has more effect on the estimation of extreme daily precipitations of return period equal or greater than ten years than the choice of the climate models.

© D. Guyomard Présentation La pêcherie palangrière réunionnaise s’est développée depuis 1991 à partir de la Réunion. Initialement ciblée sur les thonidés, la technique s’est progressivement adaptée à la capture des espadons (Xiphias gladius Linnaeus, 1758) par l’adoption du calmar comme appât, de filages le soir au coucher du soleil pour laisser la ligne dériver de nuit en subsurface et des cyalumes (bâtonnets luminescents) attirant les proies de l’espadon en surface, calmars et petits poisso...

The Dixon-Tyree stem hygrometer has hitherto been used primarily indoors in controlled conditions. We used it, and the leaf pressure chamber, to measure water potentials in plantation rubber trees outside in the Cote d’Ivoire (May and September 2004). Measurements of stem and root xylem water potentials were considered to be reliable, provided they complied with technical constraints that we specify. The stem hygrometer is non-destructive if the sensor is well installed, and provides measurements for two to three weeks without intervention, although the initial measurements are sometimes erroneous.

Debris-covered glaciers respond to atmospheric conditions in different ways from debris-free glaciers, due to the presence of debris at the surface during the ablation season and at the snow/ice interface during the accumulation season. Understanding the response of debris-covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change. To tackle this issue, we developed the Crocus-DEB model as an adaptation of the detailed snowpack model Crocus, to simulate the energy and mass balance of debris-covered glaciers, including periods when debris is covered by snow. Crocus-DEB was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at Col de Porte, France, with very good results in terms of conductive heat flux, both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice, with and without snow overlying the debris. The model was also evaluated using field data from the debris-covered glacier Changri Nup, Nepal, Himalaya. This paper introduces the design of the model, its performance and its ability to explore relationships between model parameters, meteorological conditions and the critical debris thickness.

Dinitrogen-fixing organisms in cyanobacterial mats were studied in two shallow coral reef ecosystems: La Reunion Island, southwestern Indian Ocean, Sesoko (Okinawa) Island, and northwestern Pacific Ocean. Rapidly expanding benthic miniblooms, frequently dominated by a single cyanobacterial taxon, were identified by microscopy and molecular tools. In addition, nitrogenase activity by these blooms was measured in situ. Dinitrogen fixation and its contribution to mat primary production were calculated using (15)N(2) and (13)C methods. Dinitrogen-fixing cyanobacteria from mats in La Reunion and Sesoko showed few differences in taxonomic composition. Anabaena sp. among heterocystous and Hydrocoleum majus and Symploca hydnoides among nonheterocystous cyanobacteria occurred in microbial mats of both sites. Oscillatoria bonnemaisonii and Leptolyngbya spp. occurred only in La Reunion, whereas Hydrocoleum coccineum dominated in Sesoko. Other mats dominated by Hydrocoleum lyngbyaceum, Phormidium laysanense, and Trichocoleus tenerrimus occurred at lower frequencies. The 24-h nitrogenase activity, as measured by acetylene reduction, varied between 11 and 324 nmoles C(2)H(2) reduced microg(-1) Chl a. The highest values were achieved by heterocystous Anabaena sp. performed mostly during the day. Highest values for nonheterocystous cyanobacteria were achieved by H. coccineum mostly during the night. Daily nitrogen fixation varied from nine (Leptolyngbya) to 238 nmoles N(2) microg(-1) Chl day(-1) (H. coccineum). Primary production rates ranged from 1,321 (S. hydnoides) to 9,933 nmoles C microg(-1) Chl day(-1) (H. coccineum). Dinitrogen fixation satisfied between 5% and 21% of the nitrogen required for primary production.

Using three daily measurements of wind speed and direction from synoptic weather station data in SE Niger, we examined the diurnal, seasonal and interannual time-scale of Sahel climate variability between 1950 and 1992. The seasonal wind patterns are closely related to the temperatures and West African monsoon dynamics. The transitions between the two seasons are marked by an important increase in calms (wind speed < 0.5 m s-1). Such variations are related to meridional shifts of the Inter Tropical Discontinuity (ITD) and Inter Tropical Convergence Zone (ITCZ). Interannual fluctuations of annual wind speeds are consistent with Sahel rainfall variability. Dry years, such as in 1969-1973 and 1983-1986 periods, are associated with negative anomalies in wind speeds mainly due to an increase in calms and dry conditions. Nevertheless, we note several differences: the first period is associated with a yearly increase in the annual mean speed, while the second is associated with a decrease. Differences could be related to changes in atmospheric circulation, especially regarding the strength and latitudinal position of Tropical and African Easterly jets.

A travers une démarche expérimentale de simulation de la circulation routière pour estimer les pollutions atmosphériques en milieu urbain, cette proposition questionne les opportunités qu'offre la simulation multi-agents pour intégrer des données d'observations du trafic routier au sein d'un système d'information géographique. Pour cela, la construction du modèle d'affectation s'est faite en deux étapes : une première, d'acquisition et de structuration des données de comptages et une seconde visant à interfacer ces données au sein d'une plateforme de simulation multi-agents pour en reproduire la variabilité intra journalière et la fréquentation routière.

International audience

International audience; The Chao Lake, located in the Yangtze basin, is the fifth largest freshwater lake in China. The lake catchment (9130 km2 ) includes the city of Hefei (3.5 million inhabitants) and a large extent of paddy fields and rural areas. The Fengle River is a tributary of the Chao Lake. It is currently subject to flood risks and inundation issues. Many changes are expected in land use and agricultural practices in the future, due to the tourist appeal of the Chao Lake shore and the fast expansion of the city of Hefei. Climate changes are also expected in this region, with a high impact on the rainfall regime. The consequences of all these changes on flood occurrence and magnitude are a major issue for the economic development of the area and tools are needed to carry out such an analysis. Here, a methodology is proposed for investigating the potential impact of rainfall regime change on flood duration and frequencies in the future. The methodology consists of three steps: first from a literature review scenarios of changes in precipitation are identified and used to build future series of daily rainfall; secondly, future daily discharges are simulated using a distributed hydrological model (MERCEDES) previously calibrated on current rainfall–discharge data; finally the current vs future discharge dynamics are characterized in terms of flood frequencies from discharge–duration–frequency curves. The methodology is implemented on the Fengle River, for which 20 years of daily discharges (Taoxi station), daily rainfall (eight stations), temperature and evapotranspiration (Hefei weather station) are available.

International audience

The horizontal and vertical movements of large bigeye tuna (#Thunnus obesus$ Lowe, 1839 ; 25 to 50 kg) captured in the south Pacific Ocean (French Polynesia) were determined using pressure-sensitive ultrasonic transmitters. Bigeye tuna swam within the first 100 m below the surface during the night-time and at depths between 400 and 500 m during the daytime. The fish exhibited clear relationships with the sound scattering layer (SSL). They followed its vertical movements at dawn and dusk, and were probably foraging on the organisms of the SSL. Bigeye tuna did, however, make regular rapid upward vertical excursions into the warm surface layer, most probably in order to regulate body temperature and, perhaps, to compensate for an accumulated oxygen debt (i.e. to metabolize lactate). The characteristics of these dives differ from those reported from previous studies on smaller bigeye tuna (approximately 12 kg) near the main Hawaiian Islands. During the daytime, the large fish in French Polynesia made upward excursions approximately only every 2.5 h, whereas smaller fish in Hawaiian waters made upward excursions approximately every hour. Our data are the first observations on the role of body size in the vertical behavior of bigeye tuna. (Résumé d'auteur)

A process-based model for semi-arid grassland ecosystems was developed. It is driven by standard daily meteorological data and simulates with a daily time step the seasonal course of root, aboveground green, and dead biomass. Water infiltration and redistribution in the soil, transpiration and evaporation are simulated in a coupled water budget submodel. The main plant processes are photosynthesis, allocation of assimilates between aboveground and belowground compartments, shoots and roots respiration and senescence, and litter fall. Structural parameters of the canopy such as fractional cover and LAI are also simulated. This model was validated in southwest Arizona on a semi-arid grassland site. In spite of simplifications inherent to the process-based modelling approach, this model is useful for elucidating interactions between the shortgrass ecosystem and environmental variables, for interpreting H2O exchange measurements, and for predicting the temporal variation of above- and belowground biomass and the ecosystem carbon budget.

Knowledge on test conditions that may influence behavioral responses of mosquitoes is critical when excito-repellency tests are conducted. The objective of this study was to investigate the effect of test time differences on normal circadian activity and behavioral responses of field and colonized Aedes aegypti (L.) ( = Stegomyia aegypti) and Culex quinquefasciatus Say to DEET, one of the most common synthetic repellent active ingredients available. Two field populations of Ae. aegypti and Cx. quinquefasciatus from Kanchanaburi and Nonthaburi provinces, respectively, and two long-standing laboratory populations, Ae. aegypti obtained from the U.S. Department of Agriculture, and Cx. quinquefasciatus from the Ministry of Public Health, Thailand, were used. Each population was exposed to DEET during two different periods of time (0900–1500 hours) and (2100–0300 hours). Both field and laboratory Cx. quinquefasciatus showed marked differences in spatial repellent escape responses between day and nighttime periods but none in direct contact tests. No significant differences between day and nighttime testing periods were observed with field or laboratory Ae. aegypti, except a higher daytime escape response from noncontact DEET treatment. This study indicates that test time may influence the behavioral avoidance responses and is a potential confounder of excitorepellency evaluations.

Bifrequency acoustic data, hydrological measurements and satellite data were used to study the vertical distribution of macrozooplankton in the Bay of Biscay in relation to the hydrological conditions and fish distribution during spring 2009. The most noticeable result was the observation of a ‘biocline’ during the day i.e., the interface where zooplankton biomass changes more rapidly with depth than it does in the layers above or below. The biocline separated the surface layer, almost devoid of macrozooplankton, from the macrozooplankton-rich deeper layers. It is a specific vertical feature which ties in with the classic diel vertical migration pattern. Spatiotemporal correlations between macrozooplankton and environmental variables (photic depth, thermohaline vertical structure, stratification index and chlorophyll-a) indicate that no single factor explains the macrozooplankton vertical distribution. Rather a set of factors, the respective influence of which varies from region to region depending on the habitat characteristics and the progress of the spring stratification, jointly influence the distribution. In this context, the macrozooplankton biocline is potentially a biophysical response to the search for a particular depth range where light attenuation, thermohaline vertical structure and stratification conditions together provide a suitable alternative to the need for expending energy in reaching deeper water without the risk of being eaten.

In the framework of the HAPEX-Sahel experiment, a data set was gathered on a fallow savannah site of the Central East Supersite. This includes 54 days of atmospheric forcing (air temperature and humidity, wind speed, solar and long-wave radiation and rainfall), net radiation, sensible, latent and soil heat fluxes and soil temperature series at a time step of 20 min. Furthermore, 17 soil moisture profiles, the evolution of the leaf area indices and some soil characteristics were available. The data set was used, at the field scale, to calibrate and validate the SiSPAT (simple soil plant atmosphere transfer) model, a 1D model of coupled heat and mass transfer in the soil-plant-atmosphere continuum. The objectives of the study were (i) to assess the performances of the model in the prediction of the diurnal cycle of net radiation, turbulent fluxes, soil temperatures and the evolution of soil water content over a period of 54 days (day of the year 239–292, 1992), characterized by early stage intense rainfall events and fast drying afterwards, (ii) to analyse the influence of soil surface crust on the water balance and (iii) to identify the 1D modelling limits when the surface area consists of two strates: a ground sparse herb layer, characterized by a large spatial variability of surface properties and water content with scattered bushes. The model was calibrated over a 2-week period and then run over the whole 54-day period. We were able to reproduce the main characteristics of the observed net radiation, turbulent fluxes, soil temperature and soil moisture for the intense rainfall events and for an elongated dry period. Nevertheless, when the crust was not taken into account, the rainfall-runoff-infiltration process and the evapotranspiration after rain were poorly predicted (overestimation of evapotranspiration of infiltration). When a crust was considered to model the water balance at the field scale, its influence was found to be substantial on the runoff generation and the infiltration, and consequently on the bare soil evaporation. However, runoff predictions were much larger than the observations. Indeed, at the field scale, no runoff was generally observed. Lateral redistribution of water between crusted and noncrusted zones was observed in the plot. However, this cannot be taken into account with the presented 1D deterministic modelling. Hence further model development is needed to yield a better representation of soil water fluxes at the field scale.

Several pelagic fish species are known to associate with floating objects. However, quantitative information on the main factors that drive this associative behaviour is still lacking. Small pelagic fish offer a particularly interesting case study for this phenomenon, since the small spatial scales involved in their association with floating objects allow experimental data to be collected at a fine scale. Here, we monitored twelve acoustically-tagged bigeye scads, Selar crumenophthalmus (Carangidae), (mean fork length 16.4 cm, SD 2.1 cm) around a floating object moored in shallow water (15 m depth) playing the role of a coastal fish aggregating device (FAD). To quantify the role played by variations in current and daylight, we calculated the speed distribution, pair correlation function and group polarization for the tagged fish hourly, from midday to dusk (13:00–18:00), for varying current strengths and daylight conditions. We found that the current induced a shift in the position of the aggregation upstream of the FAD, at distances that increased with the current strength. We found evidence of an expansion and a higher coordination in the aggregation at dusk, with increasing speed, distance among conspecifics and alignment. We discuss possible scenarios in which group polarization increases at dusk and suggest complementary measurements for future experiments that could confirm our findings.

SUMMARYIn order to get the benefit of the growing world demand for natural rubber, Hevea brasiliensis is increasingly planted in drought-prone areas, such as in the southern part of northeast Thailand. Modelling can be a useful approach in identifying key points of improvement for rubber tree cultivation in such water-limited areas. The first objective of this study was to test the possibility of using the Water Nutrients and Light Capture in Agroforestry Systems (WaNuLCAS) model as an exploratory tool to simulate water use, growth and latex production in a pure stand on a daily basis. The second was to evaluate the relative accuracy of predictions with the current model version. Finally, the third aim of this study was to identify particular parameterisations that may be adapted to improve overall prediction quality. Model outputs were compared to measurements recorded in a mature rubber tree stand of RRIM 600 clones growing in the water-limited area of northeast Thailand. The period of analysis concerned seven months of full foliation, from May to November, including a severe drought spell. Whole-tree transpiration was estimated by xylem sap flow measurement from 11 trees. The results show that the model was able to simulate daily and seasonal change of soil water content, tree transpiration, girth increment and latex production within plausible ranges. However, under detailed scrutiny, the predictions show large inaccuracies compared to the observations: soil water content (determination coefficient (R2) = 0.461, relative root mean square error (RMSErel) = 35%), tree transpiration (R2 = 0.104, RMSErel = 94%), tree girth increment (R2 = 0.916, RMSErel = 208%) and latex production (R2 = 0.423, RMSErel = 169%). As soil water content was overestimated during the driest periods, no water stress was predicted and transpiration, growth and latex production were logically overestimated during such periods. However, tree transpiration was also largely overestimated in conditions of non-limiting soil water availability with high evaporative demand. Hence, two key points of parameterisation and improvement are identified for better simulation in our conditions: the soil water balance and particularly the ratio between water infiltration and run-off, and the regulation of transpiration under high evaporative demand. In conclusion, the WaNuLCAS model is usable as an exploratory model to simulate water use, growth and production for a pure rubber tree stand. However, in our conditions of much degraded soil and high evaporative demand, the modules of soil water balance and tree transpiration require particular parameterisations and improvement.

It is generally assumed that the daily probability of survival of mosquitoes is independent of age. To test this assumption we have conducted a three-year experimental fieldwork study (20052007) at Fortaleza-CE in Brazil, determining daily survival rates of the dengue vector Aedes aegypti (L.). Survival rates of adult Ae. aegypti may be age-dependent and the statistical analysis is a sensitive approach for comparing patterns of mosquito survival. The mosquito survival data were better fit by a Weibull survival function than by the more traditionally used Gompertz or logistic survival functions. Gompertz, Weibull, or logistic survival functions often fit the survival, and the tails of the survival curves usually appear to fall between the values predicted by the three functions. We corroborate that the mortality of Ae. aegypti in semi-natural conditions may no more be considered as a constant phenomenon during the life of adult mosquitoes but varies according to the age and environmental conditions under a tropical climate. This study estimates the variability in the survival rate of Ae. aegypti and environmental factors that are related to such variability. The statistical analysis shows that the fitting ability, concerning the hazard function, was in decreasing order: Seasonal Cox, the three-parameter Gompertz, and the three-parameter Weibull, that was similar to the three-parameter logistic. The advantage of using the Cox model is that it is convenient for exploring the relationship between survival and several explanatory variables. The Cox model has the advantage of preserving the variable in its original quantitative form and of using a maximum of information. The survival analyses indicate that mosquito mortality is both age- and environment-dependent.

Latex tapping has a well-known negative effect on the long term radial growth of rubber trees (Hevea Brasiliensis). The additional carbon sink induced by latex yield is considered as the main cause. However the potential contribution of a tapping induced water stress has received little attention. In Northeast Thailand, we applied an exploring approach comparing the diel cycle of girth change between days of rest and days with tapping in conditions of relatively stable evaporative demand and soil water availability. Trees were tapped at dark in the early morning for two consecutive days and rested for one day. Five standard trees were equipped with high accuracy girth bands above the tapping panel. The sampling included one tree with additional measurements, one below the tapping cut and the other at the trunk bottom. Data were recorded at 30 min interval over 14 days at the onset of the dry season in November. Results demonstrated a significant short-term shrinkage within two hours after tapping. However, the nighttime expansion maximum diurnal shrinkage and midnight recovery were not significantly influenced by the tapping cycle. As a result the daily growth was not negatively impacted on tapping days. Finally, in conditions of low average growth, our results refute the hypothesis of a negative impact of tapping on radial growth at a daily scale through a simple dehydration. A substantial loss of turgor was confirmed but trees seem to quickly react and smooth the consequences on nighttime recovery and diurnal shrinkage.

Continuous monitoring of oceanic and atmospheric CO2 during periods of 8 to 12 days in two particular locations of the tropical Atlantic was carried out during June-August 1986. At the first location (convergence zone; about 5°N, 20°W), the ocean surface was generally slightly undersaturated with respect to the atmosphere, whereas at the second one (Guinea Dome; 12°N, 22° W), the ocean surface was an important source zone of CO2 for the atmosphere. The results of PCO2 in surface seawater, after correction of the temperature effect, show a decrease between morning and evening related to photosynthetic activity. Over a 3-day period, the CO2 concentration in the air above the ocean may vary up to ±0.6 ppm d-1 at the same location, whereas the wind direction hardly changes. The net CO2 flux changes considerably during a short period (8 to 12 days) in the same place, as does the gas transfer coefficient across the sea surface through the variation of the wind speed: the variability is about 80–90%. The net CO2 flux calculated from mean data is lower (about 30%) than the net CO2 flux calculated from data taken over short time intervals. In the Guinea Dome area in summer, the net CO2 flux can be as high (1.8 mmol m-2 d-1) as in the equatorial area.DOI: 10.1111/j.1600-0889.1989.tb00140.x

Diurnal variation in stem girth as affected by three different ranges (0.43, 1.78 and 2.11 kPa) of air vapour pressure deficit (VPD) under minimum soil water stress was studied in mature rubber trees (Hevea brasiliensis) in Northeast Thailand. Diurnal cycle of shrinkage and swelling of stem girth was observed in all ranges of VPD. Stem girth as expressed by maximum daily trunk shrinkage (MDS) decreased during the day in association with high sap flow and high VPD, and then stem girth increased during the night when VPD and sap flow were low. Stem girth fluctuation was inversely related to VPD and sap flow, especially at higher ranges of VPD. A positive and significant correlation of MDS on VPD (r = 0.42, p

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V133, P117, DOI 10.1002/qj.4 Woolnough SJ, 2000, J CLIMATE, V13, P2086, DOI 10.1175/1520-0442(2000)0132.0.CO;2 Yu LS, 2006, J CLIMATE, V19, P6153, DOI 10.1175/JCLI3970.1 Wade, Malick Caniaux, Guy duPenhoat, Yves Dengler, Marcus Giordani, Herve Hummels, Rebecca Dengler, Marcus/A-7327-2014 Dengler, Marcus/0000-0001-5993-9088 AMMA; European Community This study was supported by the AMMA project. Based on a French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, including those in France, the UK, the US, and Africa. It has been the beneficiary of a major financial contribution from the European Community's Sixth Framework Research Program. Detailed information on scientific coordination and funding is available on the AMMA International web site http://www.amma-international.org. We thank Bernard Bourles, the chief scientist of the EGEE program, and all the persons who acquired and prepared the data used in this study as well as the Captain of the RN L'Atalante and his crew for their help during the EGEE-3 cruise. We warmly thank Dr. Gregory Foltz and an anonymous reviewer for their pertinent and useful comments and remarks. 8 SPRINGER HEIDELBERG HEIDELBERG OCEAN DYNAM; A one-dimensional model is used to analyze, at the local scale, the response of the equatorial Atlantic Ocean under different meteorological conditions. The study was performed at the location of three moored buoys of the Pilot Research Moored Array in the Tropical Atlantic located at 10 degrees W, 0 degrees N; 10 degrees W, 6 degrees S; and 10 degrees W, 10 degrees S. During the EGEE-3 (Etude de la circulation oceanique et de sa variabilite dans le Golfe de Guinee) campaign of May-June 2006, each buoy was visited for maintenance during 2 days. On board the ship, high-resolution atmospheric parameters were collected, as were profiles of temperature, salinity, and current. These data are used here to initialize, force, and validate a one-dimensional model in order to study the diurnal oceanic mixed-layer variability. It is shown that the diurnal variability of the sea surface temperatures is mainly driven by the solar heat flux. The diurnal response of the near-surface temperatures to daytime heating and nighttime cooling has an amplitude of a few tenths of degree. The computed diurnal heat budget experiences a net warming tendency of 31 and 27 Wm(-2) at 0 degrees N and 10 degrees S, respectively, and a cooling tendency of 122 Wm(-2) at 6 degrees S. Both observed and simulated mixed-layer depths experience a jump between the nighttime convection phase and the well-stabilized diurnal water column. Its amplitude changes dramatically depending on the meteorological conditions occurring at the stations and reaches its maximum amplitude (similar to 50 m) at 100 degrees S. At 6 degrees and 10 degrees S, the presence of barrier layers is observed, a feature that is clearer at 10 degrees S. Simulated turbulent kinetic energy (11(E) dissipation rates, compared to independent microstructure measurements, show that the model tracks their diurnal evolution reasonably well. It is also shown that the shear and buoyancy productions and the vertical diffusion of TKE all contribute to the supply of TKE, but the buoyancy production is the main source of TKE during the period of the simulation.

A major proportion of flow in the Indus river is contributed by its snow and glacier-fed river catchments situated in the central Karakoram ranges in the northern areas of Pakistan. It is therefore essential to better understand the hydro-meteorological observations in this mountainous area for water resources management. The MODIS MOD10A2 remote-sensing database of snow cover products from march 2000 to december 2009 was selected to analyse the snow cover changes in the Hunza river basin (mean hypsometric elevation = 4631 m) (situated in the central Karakoram). A database of daily flows for the Hunza river at Dainyor bridge over a period of 40 years and climate data (precipitation and temperature) of the catchment for 12 years was made available to investigate the hydrological regimes in the area. The Snowmelt-Runoff Model (SRM) was tested for runoff simulations in the catchment, keeping in mind that application of the SRM is based on snow cover remote-sensing data as the key information. The results obtained suggest that the SRM integrated with remotely sensed MODIS data can be used efficiently for hydrological modeling in the snow- and glacier-fed catchments of central Karakoram region.

Effects of soil and atmospheric drought on whole-tree transpiration (E-T), leaf water potential (psi(L)) and whole-tree hydraulic conductance (K-T) were investigated in mature rubber trees (Hevea brasiliensis, clone RRIM 600) during the full canopy stage in the rainy season in a drought-prone area of northeast Thailand. Under well-watered soil conditions, transpiration was tightly regulated in response to high evaporative demand, i.e., above reference evapotranspiration (ETo) similar to 2.2 mm day(-1) or maximum vapor pressure deficit similar to 1.8 kPa. When the trees experienced intermittent soil drought E-T decreased sharply when relative extractable water in the top soil was < 0.4. The midday leaf water potential (psi(md)) on sunny days did not change as a function of soil drought and remained stable at approximately -1.95 MPa, i.e., displaying isohydric behavior. The decrease in E-T was mainly due to the change in K-T. K-T remained constant over a wide range of environmental conditions and decreased sharply at low soil water availability. A simple hydraulic model incorporating critical minimum water potential and the response of whole-tree hydraulic conductance to relative extractable water correctly simulated patterns of transpiration over 6 months. We conclude that an explicit and simplified framework of hydraulic limitation hypothesis was sufficient to describe water use regulation of a mature rubber tree stand in water-limited conditions. Given the complexity of constraints in the soil-plant-atmosphere pathway, our results confirm the relevance of this approach to synthesize the overall behavior of trees under drought.

International audience; Dietary changes alter dairy cow milk fat concentration (MFC) and yield (MFY) through modifications in the supply of nutrients, which act as precursors or inhibitors of mammary fat synthesis. The current models used to formulate dairy cow diets cannot predict changes in milk fat. The knowledge of the effects of the nutrients on milk fat would help to progress toward this prediction. To this end, we quantified and compared the milk fat responses to variations in the supply of seven nutrients derived from digestion: volatile fatty acids, glucose, proteins, long-chain fatty acids (LCFA) and t10,c12-conjugated linoleic acid (CLA). A database was compiled from studies involving digestive infusions of these nutrients in dairy cows. It included 147 comparisons between a nutrient infusion and a control treatment. The nutrient infusions were limited to the range of physiological variations to mimic nutrient changes after dietary modifications. We established models for the response of MFC, MFY and milk fatty acid (FA) composition to the supply of each nutrient. MFC and MFY responses to the nutrients were significant and linear, except for the MFC response to glucose that was curvilinear. The nutrients differed in their effects on MFC and MFY: acetate, butyrate and LCFA increased MFC and MFY, whereas propionate, glucose and t10,c12-CLA decreased them. Protein infusions increased MFY and decreased MFC because of an increase in milk yield. The effects of numerous interfering factors related to animals, diets or experimental conditions were tested on the residuals of the response models. The responses of milk FA percentages are also provided. When adjusted to the in vivo variations in the nutrients observed after dietary changes, the effects of the different nutrients were moderate. Finally, this study showed that several of these nutrients could contribute to the changes in milk fat production and composition observed after dietary changes. This is a first step toward predicting milk fat response to changes in nutrient supply.

International audience; Spatial and temporal scales of variability in phyto- and bacterioplankton abundance were investigated in a deep atoll lagoon (Ahe, French Polynesia), Ahe Lagoon showed a classical phytoplankton composition, but its picophytoplankton (Prochlorococcus, Synechococcus and picoeukaryotes) concentrations are higher than the mean for Polynesian atoll lagoons. Phyto- and bacterioplankton descriptors were highly variable, with mean CVs of >20% in most cases: day night, day-to-day, vertical, lagoonal and seasonal. Phytoplankton biomass, which was estimated by in vivo fluorescence, was higher in the deep layer than in the upper layer. This pattern was detected on a day night scale, showing transitory vertical gradients, and through long-term events that were recorded during day-to-day measurements, especially during low wind conditions. The main factors potentially driving this vertical structure of the phytoplankton appeared to be photoinhibition in upper layers and a bottom effect providing more favourable nutrient conditions in deeper layers. Day-to-day fluctuation was the major source of temporal variation and appeared to be highly driven by vertical patterns and mixing events showing phytoplankton supply from deep layers. At the lagoon scale, the picophytoplankton exhibited a patchy structure that is closely linked to the geomorphology of the rim, lagoon depth and proximity of the pass. Stations close to the pass were characterized by consistently lower Synechococcus and picoeukaryote concentrations. Lastly, warm periods showed higher Synechococcus, nanophytoplankton and bacterial concentrations. Prochlorococcus and picoeukaryotes showed no seasonal trend, but had an annual variability that could be related to variations in exchanges between the lagoon and the ocean.

Monsoon rainfall is central to the climate of West Africa, and understanding its variability is a challenge for which satellite rainfall products could be well suited to contribute to. Their quality in this region has received less attention than elsewhere. The focus is set on the scales associated with atmospheric variability, and a meteorological benchmark is set up with ground-based observations from the African Monsoon Multidisciplinary Analysis (AMMA) program. The investigation is performed at various scales of accumulation using four gauge networks. The seasonal cycle is analyzed using 10-day-averaged products, the synoptic-scale variability is analyzed using daily means, and the diurnal cycle of rainfall is analyzed at the seasonal scale using a composite and at the diurnal scale using 3-hourly accumulations. A novel methodology is introduced that accounts for the errors associated with the areal–time rainfall averages. The errors from both satellite and ground rainfall data are computed using dedicated techniques that come down to an estimation of the sampling errors associated to these measurements. The results show that the new generation of combined infrared–microwave (IR–MW) satellite products is describing the rain variability similarly to ground measurements. At the 10-day scale, all products reveal high regional and seasonal skills. The day-to-day comparison indicates that some products perform better than others, whereas all of them exhibit high skills when the spectral band of African easterly waves is considered. The seasonal variability of the diurnal scale as well as its relative daily importance is only captured by some products. Plans for future extensive intercomparison exercises are briefly discussed.

The influence of meteorological variables on snow/ice melting has been analyzed for two very contrasting months, in summer 2006, on Glacier de Saint-Sorlin, French Alps. July 2006 was the warmest July since 1950, and August 2006 was the coldest August since 1979. The total energy available for melting was just over half as much in August as in July, due to a sharp decrease in net shortwave radiation and in turbulent flux. This decrease of net shortwave radiation was mainly controlled by a strong increase in albedo responsible for an increase of reflected shortwave radiation, as well as by a reduction in incident shortwave radiation. During the two months, net longwave radiation remained almost unchanged. The mass balance computed from energy-balance modelling or with a degree-day approach was in good agreement with measured mass balance. Differences were attributed to space and time surface aspect variations which mainly controlled the observed mass balance.

L'objectif de ce travail est d'estimer l'évapotranspiration réelle et la résistance du couvert d'une savane en utilisant la méthode du rapport de Bowen pour deux périodes contrastées, saison sèche et saison des pluies. La méthode du rapport de Bowen permet de quantifier l'évapotranspiration réelle de la savane à partir des mesures des gradients de température et d'humidité de l'air, du rayonnement net et du flux de chaleur dans le sol. Ses avantages en sont une rapidité de mise en place du dispositif de mesure, une résolution temporelle des mesures inférieure à une heure, une continuité des mesures, une bonne intégration des hétérogénéités du flux de chaleur latente d'évaporation du couvert. Ce dispositif est adapté aux recherches agro-météorologiques et éco-physiologiques faites en milieu tropical avec des équipes restreintes. La fiabilité de cette méthode a été appréciée par comparaison avec l'équation Monteith et la méthode de l'équation du bilan hydrique. Cette savane est dominée à 90% par Loudetia arundinacea (Pointe Noire, Congo). Les résultats présentés sont issus de mesures qui ont duré 24 jours, du 18 septembre au 11 octobre 1998 : (a) du 18 au 29 septembre (" saison sèche "), la rétention en eau du sol a été inférieure à 70% de la réserve à la capacité au champ (de 63 à 70% de RCC ; stress hydrique sévère ; T/ETP de 0,2 à 0,4) ; (b) du 30 septembre au 11 octobre (" saison des pluies "), la rétention en eau du sol a été de 90 à 92% de RCC ; stress hydrique négligeable ; T/ETP de 0,73 à 0,77). La résistance du couvert moyenne journalière issue du rapport de Bowen a été de 317 s m-1, avec 355 s m-1 pour la " saison sèche " et de 279 s m-1 pour la " saison des pluies ". Les valeurs de l'ETR cumulée de la savane issues du rapport de Bowen, de la méthode du bilan hydrique et de l'équation de Penman-Monteith sont respectivement de 58,6, 57,8 et 56,2 mm, avec une ETR moyenne journalière de 2,4-2,4 et 2,3 mm jour-1, l'ETR moyenne journalière étant de 2,4, 1,5 et 2,2 mm jour-1 en " saison sèche " et de 2,5, 3,4 et 2,5 mm jour-1 en " saison des pluies ".

Quantification of ammonia (NH3) land-atmosphere exchange is required for atmospheric modelling and assessment of nitrogen deposition, yet flux measurement methods remain highly uncertain. To address this issue, a major inter-comparison of ammonia fluxes over intensively managed grassland was conducted during the GRAMINAE Integrated Experiment held in Braunschweig, Germany. In order to provide a robust dataset of ammonia exchange with the vegetation, four independent continuous flux gradient systems were operated. Three independently operated continuous wet denuders systems (AMANDA) were compared with a Wet Effluent Diffusion Denuder (mini-WEDD) system. Measurements were made at two distances from an adjacent livestock farm, allowing effects of advection to be quantified in a real landscape setting. Data treatment included filtering for instrument failure, disturbed wind sectors and unsuitable micrometeorological conditions, with corrections made for storage and advection errors. The inter-comparison demonstrated good agreement in measured ammonia concentrations and fluxes (relative standard error 3 m−2 s−1), b) larger diurnally-varying emissions following cutting (−49 to 703 ng NH3 m−2 s−1) and c) much larger emissions following fertilizer application (0 to 3820 ng NH3 m−2 s−1). The results are a salutary reminder of the uncertainty in unreplicated ammonia flux measurements, while the replication of the present study provides a uniquely robust dataset for the evaluation of ammonia exchange processes. It is clear that consistently reliable determination of ammonia concentrations remains the major measurement challenge.

Several studies showed that remote sensing data appear as an appropriate solution for accurately locating ponds over large areas, but there are few studies on the temporal aspect to monitor their dynamics. Here, we presented a method to monitor ponds hydrological dynamics (filling/emptying) in arid lands using a time series of MODIS/TERRA images. We studied two consecutive rainy seasons 2001 and 2002 for which we had corresponding measurements of daily water level data on several ponds. The study was conducted within a radius of approximately 13* 13 km around the village of Barkedji (15.22°N, 14.86°W) located in the Ferlo region in North-East Senegal. This area is characterized by a complex and dense network of ponds that are filled during the rainy season. To evaluate MODIS images ability to capture pond dynamics, we calculated the correlation between the NDVI pixel value and the water level data collected at three ponds (Mous, Furdu and Barkedji) using an empirical temporal cross-covariance method. The temporal study showed very good results with a maximum of cross-covariance (Mous: cov=0.69; Furdu: cov=0.77; Barkedji: cov=0.83) for [delta]t=-6 days for Mous and Furdu and [delta]t=-10 days for Barkedji pond, suggesting that multi-temporal MODIS-NDVI data can prove very efficient for monitoring the state and dynamics of little ponds (about 2000 m2) in and lands. (Texte intégral)

Experimental studies indicate that evaporative fraction (EF), the ratio between the latent heat flux and the available energy at the land surface, is a normalized diagnostic that is nearly constant during daytime under fair weather conditions (so-called daytime selfpreservation). This study examines this observation and investigates contributions to the variability of EF due to environmental factors (air temperature, solar incoming radiation, wind velocity, soil water content or leaf area index). It is shown here that the phase difference between soil heat flux and net radiation needs to be characterized fully in application models that invoke EF daytime self-preservation. Further conditions under which the diurnally constant EF assumption can hold are also discussed. # 2006 Elsevier B.V. All rights reserved.

L12609; We investigate the impact of submonthly rain fluctuations on the daily-to-interannual variations of the salinity in the tropical Indian Ocean. A three-year record of daily observed precipitation and wind are used to force an Indian Ocean model in two experiments that differ only by their rain forcing, which is either daily- (Exp_day) or monthly- (Exp_month) averaged. Results show that submonthly precipitations significantly impact the Surface Layer Salinity (SLS) in the northern and eastern Bay of Bengal during the wet season from May to November. In September when the Bay reaches its SLS minimum, the Andaman Sea is saltier by as much as 1.3 psu for Exp_day. The frequency shift between the submonthly rain forcing and the yearly salinity response is due to accumulation in time of nonlinear mechanisms: sudden rain deficits increase the SLS by entraining salty waters from below, whereas rain excesses are inefficient to decrease the salinity of the thick surface layer.