A proposal for risk zonation in urban river basins is presented. The proposed methodology combines specific natural hazard with vulnerability indicators developed for that hazard in order to produce the estimation of risk for that specific hazard. The proposed methodology is based in the construction of thematic maps for the specific hazard and related vulnerability, which will allow to make combinations of those maps by means of the algebra of maps and decision rules in order to define the risk maps. The proposed methodology consist then in developing a risk, hazard and vulnerability maps specific for each natural hazard condition such as floods, earthquakes and land slides. This is opposed to the traditional zonation methodology consisting in the construction of only one risk map, resulting from the weighted combination of maps for the total hazard and for the total vulnerability. Finally results obtained in an urban river basin of the city of Medellin, Colombia, are presented. PALABRAS CLAVES: Riesgo, Amenaza, Planificacion de cuencas Planificacion de los Recursos HidricosMonferrer