On the prediction of the Toce Alpine Basin Floods with Distributed Hydrologic Models

With the objective of improving flood predictions, in recent years sophisticated continuous hydrologic models including complex land surface sub-models have been developed. This has produced a significant increase in parameterization; consequently, applications of distributed models to ungaged basins lacking specific data from field campaigns may become redundant. The objective of this paper is to produce a parsimonious and robust distributed hydrologic model for flood predictions in Italian Alpine basins. Application is made to the Toce basin (area of 1534 km2). The Toce basin was a case study of the RAPHAEL European Union research project, during which a comprehensive set of hydrologic, meteorological and physiographic data were collected, including the hydrologic analysis of the 1996-1997 period. Two major floods occurred during this period. We compare the FEST04 event model, which computes rainfall abstraction and antecedent soil moisture conditions through the simple SCS-CN method, and two continuous hydrologic models, SDM and TDM, which differ in soil water balance scheme, and base flow and runoff generation computations. The simple FEST04 event model demonstrated good performance in the prediction of the 1997 flood, but shows limits in the prediction of the long and moderate 1996 flood. More robust predictions are obtained with the parsimonious SDM continuous hydrologic model, which uses a simple one-layer soil water balance model and an infiltration excess mechanism for runoff generation, and demonstrates good performance in both long-term runoff modeling and flood predictions. Instead, the use of a more sophisticated continuous hydrologic model, the TDM, that simulates soil moisture dynamics in two-layers of soil, and computes runoff and base flow using some TOPMODEL concepts, does not seem to be advantageous for this Alpine basin