Estimating direct groundwater recharge using a simple water balance model - sensitivity to land surface parameters

Periods of below average rainfall in the UK have emphasised the need for reliable estimates of groundwater recharge. Simple water balance models are often used to estimate direct groundwater recharge, but a significant effort is required to determine the land surface parameters. This paper describes a sensitivity analysis of such a model to determine the parameters having the greatest influence on estimates of recharge. The results of varying the vegetation canopy parameters for forest, and permanent and annual short vegetation, were analysed, in addition to varying the parameters of the soil moisture model. There were significant differences between the three land cover types but recharge estimates were relatively insensitive to the vegetation canopy parameters for short vegetation. However, principally due to the inclusion of a model of rainfall interception, recharge estimates were sensitive to the forest canopy parameters. Sensitivity to the parameters of the soil moisture model, particularly the rooting depth, and fractional available water content and fractional field drainable water, was found to be very high. (C) 1998 Elsevier Science B.V. All rights reserved.