Estimating areal snowmelt infiltration into frozen soils

An algorithm for estimating areal snowmelt infiltration into frozen soils i s developed. Frozen soils are grouped into classes according to surface ent ry condition as: (a) Restricted-water entry is impeded by surface condition s, (b) Limited-capillary flow predominates and water entry is influenced pr imarily by soil physical properties, and (c) Unlimited-gravity flow predomi nates and most of the meltwater infiltrates. For Limited soils cumulative i nfiltration over time is estimated by a parametric equation from surface sa turation. initial soil moisture content (water + ice), initial soil tempera ture and infiltration opportunity time. Total infiltration into Unlimited a nd Limited soils is constrained by the available water storage capacity. Th is constraint is also used to determine when Limited soils have thawed. The minimum spatial scale of the infiltration model is established for Limi ted soils by the variabilities in surface saturation, snow water equivalent , soil infiltrability, soil moisture (water + ice) and depth of soil freezi ng. Since snowmelt infiltration is influenced by other processes and factor s that affect snow ablation, it is assumed that the infiltrability spatial scale should be consistent with the scales used to describe these variables . For open, northern, cold regions the following order in spatial scales is hypothesized: frozen ground greater than or equal to snowmelt greater than or equal to snow water equivalent greater than or equal to frozen soil inf iltrability greater than or equal to soil moisture (water + ice) and snow w ater. For mesoscale application of the infiltration model it is recommended that the infiltrability scale be taken equal to the scale used to describe the a real extent and distribution of the water equivalent of the snowcover that covers frozen ground. Scaling the infiltrability of frozen soils in this ma nner allows one to exploit established landscape-stratification methodology used to derive snow accumulation means and distribution. Scaling of soil infiltrability at small scales (microscale) is complicated and requires information on the association(s) between the spatial distribu tions of soil moisture (water + ice) and snow water. A flow chart of the algorithm is presented. Copyright (C) 2001 John Wiley & Sons, Ltd.