Step by step development of HIRM-KW: A field-scale runoff model

One of the major causes of land degradation and loss of fertility is the soil erosion due to water runoff. In Italy, 77% of the territory is estimated to be threatened by accelerated erosion, because of both its natural structure and anthropic action. This leads to the need of developing modelling tools able to provide useful information for runoff risk assessment. This paper presents a detailed description of HIRM-KW (Hydrological Infiltration Runoff Model-Kinematic Wave), a physics-based hydrological model for simulating the dynamics of water runoff and infiltration in lowland soils. The model was developed by coupling a Kinematic Wave model with the Smith-Parlange infiltration theory and by making use of the basic laws of motion. Moreover, it was built up step by step in order to obtain a system of equations, lending itself to numerical treatment. HIRM-KW performances were evaluated, for demonstration purposes, by comparing the results of three simulations with corresponding outputs provided by EUROSEM (European Soil Erosion Model), resulting in a good degree of agreement. HIRM-KW is implemented by a freeware software and the executable program can be requested to the Authors.