MODEL ACCURACY IN SNOWMELT-RUNOFF FORECASTS EXTENDING FROM 1 TO 20 DAYS

This paper examines the performance of snowmelt-runoff models in condi tions approximating real-time forecast situations. These tests are one part of an intercomparison of models recently conducted by the World Meteorological Organization (WMO). Daily runoff from the Canadian snow melt basin Illecille-waet 1155 km2, 509-3150 m a.s.l.) was forecast fo r 1 to 20 days ahead. The performance of models was better than in a p revious WMO project, which dealt with runoff simulations from historic al data, for the following reasons: (1) conditions for models were mor e favorable than a real-time forecast situation because measured input data and not meteorological forecast inputs were distributed to the m odelers; (2) the selected test basin was relatively easy to handle and familiar from the previous WMO project; and (3) all kinds of updating were allowed so that some models even improved their accuracy towards longer forecast times. Based on this experience, a more realistic fol low-up project can be imagined which would include temperature forecas ts and quantitative precipitation forecasts instead of measured data.