The revised analytical model to predict rainfall interception by sparse canopies (Journal of Hydrology 170 (1995) 79) is further modified to improve the description of evaporation from wet vegetation whose canopy characteristics vary in time (e.g. agricultural crops, deciduous forest, fast-growing plantation forest, effects of storms, pests or logging, etc.). The main adjustments proposed are based on the following assumptions: (1) the canopy capacity is linearly related to leaf area index; (2) the evaporation rate from a saturated canopy can be expressed as an exponential function of leaf area index; and (3) evaporation from stems during the storms may be treated in a similar manner as that from the canopy. The comparative performance of the revised and the presently proposed version of the analytical model in predicting interception by a mixed cropping system in West Java, Indonesia is discussed in a companion paper (Part 2). © 2001 Elsevier Science B.V.