Erosion and Sediment Yield: Global and Regional Perspectives (Proceedings of the Exeter Symposium, July 1996). IAHSPubl.no. 236, 1996. 3 Erosion and sediment yield: a global overview D. E. WALLING & B. W. WEBB Department of Geography, University of Exeter, Exeter EX4 4RJ, UK Abstract The classic monograph Climat et Erosion published by Fournier in 1960 provided a valuable demonstration of the potential for using information on the sediment loads of the world's rivers to study the global denudation system. Such early work was hampered by lack of data for many areas of the world, but recent improvements in data availability now afford a meaningful basis for estimating the total suspended sediment flux from the land to the oceans and for establishing the global pattern of sediment yield and its major controls. The lack of long-term records for most rivers precludes detailed assessment of the role of anthropogenic activity in modifying the global denudation system but there is now a wide range of evidence to demonstrate the importance of such changes, in terms of both increases and decreases in sediment flux. Analysis of available longer-term records provides an important means of assessing the sensitivity of sediment yields to environmental change, which in turn requires consideration of the impact of both human activity and climate change. INTRODUCTION It was 35 years ago that Frédéric Fournier published his classic monograph entitled Climat et Erosion, which attempted to review existing information on the sediment yields of world rivers and to establish the primary controls on the global pattern of denudation (Fournier, 1960). Founder's monograph represents an important milestone in the development of our understanding of the global denudation system, since it emphasized the potential for using river load data to assess global patterns of erosion and land denudation. Subsequent increases in data availability have inevitably caused some of Fournier's assumptions and conclusions to be questioned and revised, but his study has provided the foundation for a wide range of subsequent work aimed at developing an improved understanding of the global denudation system (cf. Jansson, 1982, 1988; Milliman & Meade, 1983; Walling, 1985; Walling & Webb, 1983). This contribution attempts to provide an overview of our current knowledge of global sediment yields and to identify outstanding uncertainties and research needs. MAGNITUDE CONSIDERATIONS Data availability Working in the 1950s, Fournier had access to only limited information regarding the suspended sediment loads of world rivers, and his data-base extended to only 96 rivers.