Infiltration into frozen and unfrozen soils is critical in hydrology,controlling active layer soil water dynamics and influencing runoff. FewLand Surface Models (LSMs) and Hydrological Models (HMs) have beendeveloped, adapted or tested for frozen conditions and permafrost soils.Considering the vast geographical area influenced by freeze/thaw processesand permafrost, and the rapid environmental change observed worldwide inthese regions, a need exists to improve models to better represent theirhydrology.In this study, various infiltration algorithms and parameterisation methods,which are commonly employed in current LSMs and HMs were tested againstdetailed measurements at three sites in Canada's discontinuous permafrostregion with organic soil depths ranging from 0.02 to 3 m. Field data fromtwo consecutive years were used to calibrate and evaluate the infiltrationalgorithms and parameterisations. Important conclusions include: (1) thesingle most important factor that controls the infiltration at permafrostsites is ground thaw depth, (2) differences among the simulated infiltrationby different algorithms and parameterisations were only found when theground was frozen or during the initial fast thawing stages, but not afterground thaw reaches a critical depth of 15 to 30 cm, (3) despitesimilarities in simulated total infiltration after ground thaw reaches thecritical depth, the choice of algorithm influenced the distribution of wateramong the soil layers, and (4) the ice impedance factor for hydraulicconductivity, which is commonly used in LSMs and HMs, may not be necessaryonce the water potential driven frozen soil parameterisation is employed.Results from this work provide guidelines that can be directly implementedin LSMs and HMs to improve their application in organic covered permafrostsoils.
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