Snowmelt runoff models

Models that predict meltwater runoff at a daily timescale are important in water resource management, flood hazard assessment and climate-change impac t studies. This article identifies four basic components of such models: me teorological extrapolation, snowmelt estimation at a point, snow-cover depl etion and runoff routing. Alternative ways of handling these are discussed, with emphasis on the contrasting treatments in two widely used models: HBV and SRM. Many of the issues in meltwater modelling reflect wider debates i n hydrological and environmental modelling, including problems of complexit y vs. simplicity, the appropriate level of spatial disaggregation, paramete r identification and calibration, and internal validation. In reviewing cur rent trends emphasis is placed on the potential and Limitations of fully di stributed models, problems in using energy-balance rather than temperature- index melt models at basin scale, ways to deal with spatial variability in snow cover, and the value and limitations of earth observation data.