A New Land Surface Hydrology within the Noah-WRF Land-Atmosphere Mesoscale Model Applied to Semiarid Environment: Evaluation over the Dantiandou Kori (Niger)

Land-atmosphere feedbacks, which are particularly important over the Sahel during the West African Monsoon (WAM), partly depend on a large range of processes linked to the land surface hydrology and the vegetation heterogeneities. This study focuses on the evaluation of a new land surface hydrology within the Noah-WRF land-atmosphere-coupled mesoscale model over the Sahel. This new hydrology explicitly takes account for the Dunne runoff using topographic information, the Horton runoff using a Green-Ampt approximation, and land surface heterogeneities. The previous and new versions of Noah-WRF are compared against a unique observation dataset located over the Dantiandou Kori (Niger). This dataset includes dense rain gauge network, surfaces temperatures estimated from MSG/SEVIRI data, surface soil moisture mapping based on ASAR/ENVISAT C-band radar data and in situ observations of surface atmospheric and land surface energy budget variables. Generally, the WAM is reasonably reproduced by Noah-WRF even if some limitations appear throughout the comparison between simulations and observations. An appreciable improvement of the model results is also found when the new hydrology is used. This fact seems to emphasize the relative importance of the representation of the land surface hydrological processes on the WAM simulated by Noah-WRF over the Sahel

APPLICATION OF SATELLITE REMOTE SENSING TO ESTIMATE AREAL EVAPOTRANSPIRATION OVER A WATERSHED

International audienceA method for estimating areal evapotranspiration by using synoptical weather data and satellite imagery is presented. Recent studies have shown that if atmospheric and surface parameters are known, the energy and hydraulic budgets at the soil/vegetation]atmosphere interface can be simulated. Then, soil temperature estimated by thermal infrared remote sensing can be used to derive the energy fluxes as far as they are the equilibrium term of the energy budget. This methodology has been applied in southwestern Finland over the Eurajoki River basin. The model was first calibrated with ground measurements and satellite data. The NDVI and the surface temperature estimated from NOAA/AVHRR data have been used to calibrate the leaf area index and the minimum resistance to evapotranspiration. The different land use classes over the river basin were interpreted from LANDSAT/TM images, and the model was then run over the whole month of July 1988 for all the most important soil and vegetation types of the river basin. Finally, the total derived evaporation was compared with the one estimated by a water balance method applied over the month of July

Assimilation of soil moisture inferred from infrared remote sensing in a hydrological model over the HAPEX-MOBILHY region

International audienceHydrological models are generally unable to simulate correctly water exchanges at the soilatmosphere interface and the time evolution of surface soil humidity. This drawback often leads to poor simulation of water flows after periods of low flows because of the wrong estimation of the surface soil water content. In this paper, we describe how remote sensing can be used to account for the vegetation in the estimation of the actual evapotranspiration, and to estimate soil moisture regularly throughout the year and use it to correct the model simulation. This work has been done on the Adour river basin, in the framework of the HAPEX-MOBILHY experiment. The results presented show the improvements that result from the use of remote sensing data in hydrological modelling: better simulation of the soil moisture and of water flows at the outlets, and more realistic calculation of evaporation

Assimilation de données d’état hydrique des sols pour la modélisation des débits

National audienceLes travaux présentés dans ce chapitre couplent les approches développées en physique de l’atmosphère pour les schémas de surface (assimilation des humidités du sol) à celles développées en hydrologie pour la prévision des crues (assimilation des débits). Nous présentons les méthodes mises au point sur le bassin de l’Orgeval et plus largement étendues sur quelques sous-bassins de la Seine pour réajuster un modèle hydrologique à partir de l’assimilation d’observations d’humidité du sol et de débits

USE OF THERMAL INFRARED REMOTE SENSING FOR WATER BUDGET STUDIES

International audienceWe have developed in our group an interface model which simulates the thermal and hydraulic exchanges between the soil, the vegetation and the atmosphere and estimates the energy fluxes at the surface. This model has been shown to be able to assimilate thermal infrared and microwave data for calibration of some surface parameters. It has been used over different regions and different periods of the year. Recentresults will be presented. A first study in the frame of the HAPEX-MOBILHY experiment,(1985-1986) has shown that satellite thermal infrared and visible data may be used to calibrate the soil and the vegetation functional parameters of the model and estimate during the year either the soil moisture in the surface layer or the water available in the root zone at a scale compatible with the grid of an hydrological model. The second study is the application of this method over a Finnish watershed continuously over the month of July 1988. The total evapoiranspiration has been estimated and compared to the estimate given by a water balance method

Comparison of measured and SISPAT-RS simulated brightness temperatures and reflectances at field scale during ReSeDA experiment

International audienceThe Simple Soil-Plant-Atmosphere Transfer - Remote Sensing (SiSPAT-RS) model was developed to simulate soil-vegetation-atmosphere energy and water transfers as well as remote sensing measurements at field scale, in the visible and thermal infrared domains. This model has been validated on the Alpilles-ReSeDA (Remote Sensing Data Assimilation) experimental database gathering micrometeorological data and remote sensing observations. Sensitivity and uncertainty studies were performed with the SVAT model and the radiative transfer models using stochastic technics like Monte Carlo's methods. The results permit us to quantify the model uncertainties linked to parameters and initial conditions uncertainties, such information which is essential to carry on assimilation studies. Here, we present the results concerning the sensitivity analysis and the results of the calibration on an experimental agricultural field of ReSeDA experiment