Appropriate scales for hydro-climatological variables in the Red River basin

Decision support systems (DSSs) in water management should preferably consist of appropriate models, which are complex enough to represent important processes at a balanced level, but not unnecessarily refined, taking into account research objectives, data availability and uncertainties. This idea is illustrated by applying a methodology for the determination of appropriate scales to the hydrological part of a DSS. The variability of a relevant variable at the point scale, the discharge at the outlet, is used to determine the appropriate temporal scale. The appropriate spatial scale for precipitation is then determined at this appropriate temporal scale. Results indicate an appropriate temporal scale varying between 12 h for middle-sized upstream areas to 48 h for the complete river basin, accepting an aggregation error of 10%. The appropriate spatial scale for precipitation for the complete river basin is about 80 km. The appropriate scales found are important for the hydrological model set-up and may indicate the requirements for downscaling from climate model to hydrological model scale for climate impact assessments.