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24, chemin de Borde Rouge -Auzeville - CS52627 31326 Castanet Tolosan cedex - France

Last update: May 2021

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Modeling and Simulation

Modelling plays an integral part in UREP research activities. UREP benefits from a dedicated modelling platform which has been designed to host the different models that we use (PaSim, FarmSim, ...), as well as generic models (VulClim) integrating up- and down-scaling tools.

The modelling platform comprises:

- 6 computer workstations (including two laptops) equipped with high-frequency microprocessors and SSD hard disks with a large RAM capacity (32 GB) in order to optimize calculation capacities.

- 1 calculation server (clt-hpcurep-s) hosted in the Crouël server room and only accessible onsite via a dedicated remote terminal.

- 1 workstation dedicated to mapping, equipped with the QGis software, a high-performance video card and a large storage capacity.

Data security is assured by shared storage facilities managed by the EIC-Centre ARA and the DSI-INRAE.


UREP hosts the flagship grassland biogeochemical cycling models: PaSim. This model simulates field-scale fluxes in carbon, nitrogen, water and energy at the interface between soil, vegetation, animals and atmosphere. PaSim is composed of several sub-models representing the processes of vegetation, microclimate, biology and soil physics.

PaSim was adapted by Riedo et al. (1998) from Thornley's Hurley Pasture Model (HPM) [1998]. It was improved by Schmid et al. (2001) to simulate N2O production and emissions, and by Riedo et al. (2002) to simulate ammonia volatilization. Vuichard et al. (2007) also modified the effects of water stress and senescence on vegetation dynamics and integrated the effects of ration quality on animal methane emissions. Since then, UREP has reviewed the parameterization of water stress, changed the method for calculating N2O diffusion, added a layer of litter on the soil surface acting as an insulator, and developed a new analytical method for soil organic matter balance. An irrigation, ploughing and automated fertilization module has also been added. The code, in Fortran 90, currently contains approximately 60,000 lines.

PaSim is widely used in European (CarboEurope IP, NitroEurope IP, CARBO-Extreme) and French (CLIMATOR, VALIDATE) research projects to study the carbon and nitrogen cycles, carbon sequestration and greenhouse gas emissions in grasslands, as well as the effects of climate change and variability.

For further information, please contact Raphaël Martin.