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3rd HyMeX workshop 1-4 June 2009 Heraklion (Gournes), Crete-Greece

Space hydrology for the monitoring of Mediterranean droughts


Jean-Christophe Calvet (CNRM-GAME ( Meteo-France, CNRS)); Clément Albergel, Jean-François Mahfouf, Eric Martin

Soil moisture is a key factor of hydrological processes and plant growth, in particular in Mediterranean regions, often affected by drought. CNRM develops assimilation techniques able to integrate the surface soil moisture products derived from Earth Observation (EO) techniques in land surface models. In particular, the data of the forthcoming SMOS mission, associated to other EO data and meteorological data, will be used. Along with data assimilation techniques, CNRM implements a monitoring system of carbon and water fluxes, vegetation biomass and soil moisture over France.
A biophysical parameter monitoring system of the whole Mediterranean basin will be assessed:
First, soil moisture estimates derived from EO data (SMOS in particular), from models, and from in situ data will be compared. A soil moisture climatology will be built. Second, a monitoring system (already pre-operational over France), will be extended to the whole Mediterranean basin and evaluated with in situ and EO data.
The following tools and data will be used:
- Microwave EO soil moisture products are developping fast. Historical multi-satellite time series are available from 1978 (Owe et al. 2008). New products are being developped. In particular, the space mission SMOS (Soil Moisture and Ocean Salinity, ESA/CNES), to be launched in 2009, will permit to monitor soil moisture at the global scale, thanks to microwave radiometry at L-band (1.423 GHz, 21 cm), with a sampling time of 2-3 days and a spatial resolution of 30 to 50 km. In the future, kilometric products should be available for Mediterranean areas from the ScanSAR technique applied to the ENVISAT ASAR instrument.
- Long time series of in situ soil moisture observations permit to verify the quality of EO derived products. The SMOSMANIA network monitors soil moisture and soil temperature in Southwestern France, in real time, since 2007, at the 5,10,20,30cm depths. Twelve stations form a Mediterranean-Atlantic transect. The network was extended to Southeastern France, in the Mediterranean area. Nine more stations were equipped, in Ardeche, Gard, Herault and Vaucluse. The new stations will enable the assessment of EO products in a complex environment (strong spatial heterogeneity, relief, proximity to the sea) and to validate the modelled surface hydrology for Mediterranean soils.
- CNRM develops SURFEX (Surface Externalisee), a modelling platform including a vegetation model able to simulate the carbon fluxes. This version of SURFEX is being implemented and tested over France, with a EO data assimilation system. The system is able to monitor soil moisture and water and carbon fluxes. The model is driven by the SAFRAN atmospheric (re)-analyses. The ECMWF ERA-Interim global analysis will be evaluated over France and then applied to the Mediterranean basin. ERA-Interim will be used to drive SURFEX in order to build a soil moisture and water/carbon flux climatology for the whole Mediterranean basin, and to constrain the drought-monitoring system.