SARRA-H Crop Model______________figfigfig______________Cirad, UMR TETIS, C.Baron , 2013_fig
Système d'Analyse Régionale des Risques Agroclimatologiques Version H (SARRA-H;System of Agroclimatological Regional Risk Analysis)

Translation: Peter Biggins ............................................................................................................................................................

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fig SARRA-H, a simple and robust crop model.

    A model is a partial representation of the functioning of a system: study object. 
    The model therefore only represents processes and variables that are considered relevant and can be generalized.
    The question of the relevance of choices is linked to the objectives of the modeller, and 
    the generic nature of the chosen phenomena depends on the targeted extrapolation domain. 
    This model has been designed as a toolbox for assembling different modules bringing into play 
    an evolutionary library of formalisms (objects). Despite this flexibility and multifunctionality, 
    we remain within the field of conventional crop models: a daily time step, a plot scale, 
    the crop colonizes the soil and aerial space, gains access to available resources and produces biomass.

fig

*Daily sequence diagram for the simulated processes *

The SARRA-H model (version H) is a more detailed version of SARRA which was a simple dynamic water balance model used to estimate the impact of a climatic scenario on an annual crop. For the former SARRA version, the plant was merely a conduit linking atmospheric demand (sink) with a “useful” water reserve in the soil (source) – a conduit of variable resistance, depending on physical constraints (stress). SARRA assumed that the performance of a crop was a simple function of water stresses cumulating over a plant cycle. This simple and neat principle proved to be remarkably robust across spatial scales (from plot to region) and displayed multiple applications: i) the AGRHYMET food security early warning system for the CILSS countries (Sahel), ii) zoning, iii) local climate risk analyses, iv) estimation of water requirements, etc. Nevertheless, its validity depended on the existence of a strong water limitation and/or high spatial or temporal variability of that limitation. In other words, SARRA was entirely based on a reduction in growth, but not on the simulation of potential yield.

SARRA-H is a deterministic and relatively simple model (compared to CERES, APSIM, STICS, etc.), but it simulates more processes than AQUACROP (reference proposed by FAO). It is a model integrated into a flexible environment, managing a module library and a database. This model reproduces processes on a plot scale enabling analyses on a regional scale. Lastly, it is a model that can be used as a basic support with other scientific fields by way of complementary modules or interfaces with other models (meteorological, socio-economic, etc.). This evolutionary spirit and openness, explicitly sought by the developers, acknowledges the fact that any new application of a model for scientific research requires a more or less major adaptation of the tool. SARRA-H is integrated into a platform offering numerous tools and interfaces: data importing, data exporting (simulation scenarios, climate series, and results in different forms (aggregation, etc.), graphic representations, sensitivity analyses, etc. A database can be used for optimized data and result management. Lastly, the modular structure of this environment also enables external management of the calculation engine (simulator) independently of the environment. All these functionalities are described in a user manual.

In the same daily loop the model simulates three major processes:

figWater balance: it estimates evapotranspiration and the water stress index; the soil comprises three reservoirs: superficial, deep, and a dynamic root reservoir

figCarbon balance: it is based on the big leaf concept, it converts solar energy into sugar under water stress, then distributes it within the biomasses

figPhenology: it manages changes in phenological stages (emergence, vegetative stage, flowering, ripening) and the associated processes (germination, juvenile mortality, biomass distribution modalities, etc.).

ico Management of multiple simulation scenarios (interface or automatic activation)

figSimulation scenarios

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