TN-60 : Parameterization of infiltration in GCM

Abstract

The General Circulation Models (GCM) synthesize the large scale distribution of the climate by application of the physical laws governing the atmospheric structure and behaviour. These models are highly sensitive to near surface soil moisture and therefore the large scale changes in soil-moisture influence the predictability of the climate appreciably.

Infiltration, the process of water entry into the soil controls the moisture status in top soil layer as well as water balance of the land surface. It partitions precipitation between soil water gain and surface runoff, and the infiltration characteristics of a basin can be used to determine the rainfall excess for a given storm and hence the resulting flood. Infiltration can be best simulated in a hydrological model incorporating all the relevant processes as precipitation evapotranspiration, runoff etc. The hydrological parameterizations of surface runoff and ground water have been well achieved on catchment scales but the parameterization studies, concerning with infiltration process still lag behind. Most of the studies pertain to the problem of infiltration into a barae soil surface. Not much work has been done on infiltration into a vegetated or snow-covered surface. The parameterization of infiltrations process on a scale approaching to general circulation models has not yet been achieved for any kind of soil surfaces.

This technical note gives a review of the status of infiltration studies particularly with reference to the scale of general circulation models. The steps taken by WMO in order to understand the atmosphere-land surface interactions and hydrological processes on space and time scales have been reviewed in particular. Important developments in the theory of infiltration and the factors influencing the infiltration late have been discussed. Infiltration at different soil surfaces viz. bare, vegetated and snow-covered surfaces has been reviewed. Special emphasis has been given to discussion of infiltration characteristics for the Indian soil types.