Geographic Information Systems are computer systems capable of assembling, storing,
manipulating, and displaying geographically referenced information (Dodson, 1992; van Dijk and Bos, 2001). GIS technology appears particularly suitable for dealing with data and modeling issues associated with environments involving multi-scale processes, within a complex and heterogeneous domain. To this end, GIS can help understand spatial data issues and provide a better knowledge of physical phenomena. Most surface and groundwater simulation models are based on finite difference or finite element approximation techniques composed of numerous grid cells. With GIS, distributed model parameters can be regionalized, represented in a digital map and referenced to the modeling grid. Nowadays, GIS appear to be used mainly as pre-processors for organizing spatially distributed parameters and input data, and as post-processors for displaying and possibly analyzing model results, while GIS-embedded modeling approaches appear to be less common. It is reasonable to hope that with more powerful and affordable computer technology, the integration of GIS with hydrologic models will proceed at a faster pace in the future.
3.5 Decision Support Systems
The repeated use of simulation models, linked with spatial analysis procedures, under different hypotheses, whether for system design or operation and management purposes, is generally called Decision Support System (DSS). Decision support systems are interactive computer-based information providers. Like their underlying models and data management components, they do not make decisions. They merely provide information to those who need it or to potential beneficiaries. DSSs for water resource