An evaluation of snow accumulation and ablation processes for land surfacemodelling

This paper discusses the development and testing of snow algorithms with sp ecific reference to their use and application in land surface models, New a lgorithms, developed by the authors, for estimating snow interception in fo rest canopies, blowing snow transport and sublimation, snow cover depletion and open environment snowmelt are compared with field measurements. Existi ng algorithms are discussed and compared with field observations. Recommend ations are made with respect to: (a) density of new and aged snow in open a nd forest environments; (b) interception of snow by evergreen canopies; (c) redistribution and sublimation of snow water equivalent by blowing snow; ( d) depletion in snow-covered area during snowmelt; (e) albedo decay during snowmelt; (f) turbulent transfer during snowmelt; and (g) soil heat flux du ring meltwater infiltration into frozen soils. Preliminary evidence is presented, suggesting that one relatively advanced land surface model, CLASS, significantly underestimates the timing of snowm elt and snowmelt rates in open environments despite overestimating radiatio n and turbulent contributions to melt. The cause(s) may be due to overestim ation of ground heat loss and other factors. It is recommended that further studies of snow energetics and soil heat transfer in frozen soils be under taken to provide improvements for land surface models such as CLASS, with p articular attention paid to establishing the reliability of the models in i nvoking closure of the energy equation. (C) 1998 John Wiley & Sons, Ltd.