XXXIII Convegno Nazionale di Idraulica e Costruzioni Idrauliche Brescia, 10-15 settembre 2012 A HYDROMETEOROLOGICAL FLOOD FORECASTING SYSTEM FOR THE RED AND CA RIVERS (CHINA, LAOS AND VIETNAM) PART I – INVESTIGATED AREAS AND MODEL SETUP R. Ranzi 1 , L.A. Ngô 2 , T.T. Hoàng 2 , H.S. Nguyễn 2 , S. Barontini 1 , G. Grossi 1 , B. Bacchi 1 , A. Buzzi 3 , S. Davolio 3 , O. Drofa 3 , P. Malguzzi 3 , L.T. Đỗ 4 , V.H. Võ 4 , M.C. Vũ 2 (1) Dipartimento di Ingegneria Civile Architettura Territorio e Ambiente, Università di Brescia, Italia, e-mail: ranzi@ing.unibs.it (2) Faculty of Hydrology and Water Resources, Water Resources University, Tay Son Street 175, Dong Da District, Hanoi, Vietnam; email: ngolean80@gmail.com (3) Istituto di Scienze dell'Atmosfera e del Clima CNR-ISAC, Bologna, Italia, e-mail: a.buzzi@isac.cnr.it (4) National Center for Hydrometeorological Forecasting, Hanoi, Vietnam; email: vovanhoa@nchmf.gov.vn ABSTRACT As a result of two research projects conducted over the last six years, this paper describes the configuration a hydrometeorological flood forecasting system set up for the Red River (169 000 km² at the outlet) and the Ca River basins (23 830 km 2 at the outlet), across China and Vietnam, and Laos and Vietnam, respectively. The research objectives were to setup a hydrometeorological chain to forecast discharge flowing into reservoirs and at some control sections for flood control downstream, including the heavily populated Northern Delta and, for the Ca river, the Vinh area, both experiencing rapid development. The distributed hydrological model DIMOSHONG, which implements a modified Green-Ampt or an SCS-type soil moisture accounting scheme, is forced by Quantitative Precipitation Forecasts provided by the BOLAM and the MOLOCH meteorological models or by raingauge observations. The forecasting chain has an Extended Kalman Filtering updating module based on hydrometric measurements now available in real-time for two pilot stations installed in Ghenh Ga and Nam Dan, in the Red and Ca rivers, respectively. Several floods in the basins, including the August 1971 and October 2010 catastrophes which flooded the Red river and the Ca river regions, were simulated providing useful results in view of improving flood alert systems. INTRODUCTION Flood hazard mitigation measures have been traditionally mainly focused on structural defence systems, including river embankment, diversion, by-pass and reservoirs construction. Starting with the XIX century, non-structural measures based on flood alert systems, land planning, flood risk mapping and communication have been implemented in some areas and today are becoming an important alternative for