Ash on Snow a Tool – A Tool to Prevent Flooding?: Paper presented at the Nordic Hydrological Conference (Uppsala, Sweden – June, 2000)

Years with late spring in combination with thick snow-pack constitute risk for flooding. To decrease that risk, the possibility of spreading albedo-lowering material (wood ash) on parts of a basin snow has been examined. By blackening the snow more solar radiation is absorbed and the snowmelt is enhanced. If sun-exposed parts of the basin are ash-treated (before normal runoff starts) the runoff will be distributed over a longer period of time and the risk of flooding will be reduced. Wood ash in different concentrations was spread on small snow plots and melt rates and albedo were measured. For snow covered with 0.03 kg ash m⁻², the albedo was decreased from ≈ 0.60 for natural snow to ≈ 0.25, resulting in ≈ 90% more absorbed short-wave radiation. Melt on the ash treated surface, (daily average snow water equivalent), was 70% larger than melt on natural snow (12 and 7 mm d⁻¹ respectively). A five times larger concentration (0.15 kg m⁻²) only increased the melt rate to 14 mm d⁻¹. The temperature-index method was shown to be inadequate for modelling the melt rate for the ash treated snow. A radiation-index model, based on absorbed incoming short wave radiation, was shown to model the melt rate better than the temperature-index method.