Regional Hydrological Impacts of Climatic Change—Hydroclimatic Variability (Proceedings of symposium S6 held during the Seventh IAHS Scientific Assembly at Foz do Iguaçu, Brazil, April 2005). IAHS Publ. 296, 2005. 1 BACKGROUND AND SUMMARY Regional hydrological impacts of climate change— hydroclimatic variability STEWART FRANKS 1 & THORSTEN WAGENER 2 1 School of Engineering, University of Newcastle, Callaghan, New South Wales 2308, Australia stewart.franks@newcastle.edu.au 2 Department of Civil and Environmental Engineering, The Pennsylvania State University, 226B Sackett Building, University Park, Pennsylvania 16802, USA thorsten@engr.psu.edu INTRODUCTION Climate variability and change represent key threats to water resources systems. The provision of adequate water supply is of fundamental importance to social and economic security worldwide. As greater demands are placed upon limited resources, it becomes increasingly important to safeguard water resources systems from pollution, over-exploitation and the vagaries of climate variability and change. The challenges of water security are most acutely felt in the less developed countries. In this light, the hydrological sciences have a key role to play in providing deeper insights into the sustainability and suitable management of water resources systems. In this volume, 30 papers are presented where the main emphasis is on the quantification of climate variability and apparent change. These papers document hydroclimatic variability from a diverse range of regional areas, presenting a fair sample of climatic zones and climate threats, as well as the inherent variability of hydrological systems themselves. SOUTH AMERICA Marengo and Ronchail et al. provide insights into South American hydroclimate variability. The use of coupled ocean–atmosphere models is receiving increased attention as viable predictors of seasonal climate. Marengo presents an objective comparison of observed and modelled variability. The results indicate reasonable reproduction of seasonal and El Niño-Southern Oscillation (ENSO) variability, identifies decadal signals and points to further areas of development for GCM type approaches. Ronchail et al. evaluate 80 discharge station data against sea-surface temperatures (SST) in the Pacific and Atlantic oceans. They also evaluate decadal variability and show that significant links between Amazonian variability and SST exist with potential for prediction.