A CONCEPTUAL-MODEL OF CATCHMENT WATER-BALANCE .2. APPLICATION TO RUNOFF AND BASEFLOW MODELING

A conceptual model of catchment water balance developed in the compani on paper (Ponce and Shetty, J. Hydrol., 173: 27-40, 1995) is used to s imulate changes in runoff and baseflow with annual precipitation. The model is based on the sequential separation of annual precipitation in to surface runoff and wetting, and wetting into baseflow and vaporizat ion. Runoff is the sum of surface runoff and baseflow. Runoff gain is defined as the derivative of runoff coefficient with respect to precip itation. Baseflow gain is defined as the derivative of baseflow coeffi cient with respect to precipitation. Catchment data show that runoff a nd baseflow gains are always positive. Runoff gain reaches a peak valu e at a threshold precipitation P-rt; baseflow gain reaches a peak valu e at a threshold precipitation P-ut. Analysis of the runoff and basefl ow functions sheds additional light on the nature of the competition b etween runoff and vaporization, and baseflow and vaporization.