Coupling the ExtendSim platform with HEC-HMS for modeling irrigation strategies

The quantitative water management of the Charente River in France is a major policy concern because of freshwater scarcity in summer. In the context of SPICOSA project (Science and Policy Integration for Coastal System Assessment),) this policy issue was chosen to apply the System Approach Framework (SAF) methodology. This led to modeling irrigation management strategies to quantify its impacts on various uses. It was decided to model all sub-systems within the ExtendSim® platform as a first attempt for model-integration. For this purpose a hydrological model has been entirely programmed in ExtendSim ModL language. This allowed us to understand and quantify some interactions among the different components of the socio-ecosystem but it also revealed the limits of an “in-line” ad-hoc hydrological model. In order to lessen uncertainties and to enhance the capabilities of the model, a new version of the model has been developed with a different strategy. In a second round of development, an external hydrological model has been built in HEC-HMS (Hydrologic Engineering Center's Hydrologic Modeling System) and interfaced with ExtendSim to work as a source of forcing. This strategy has proved to be much more efficient to model water shortages without renouncing the benefits of system-modeling inside ExtendSim platform and with the advantage of a powerful software dedicated to hydrological modeling. Using this experiment, the paper discusses the case of “in-line”, “on-line” or “off-line” coupling modes to serve the objectives of policy orientated complex socio-ecosystems modeling. This research has been funded under the “Global Change and Ecosystem” priority of the 6th RTD Framework Program of the European Union.