KEY ISSUES ON CONTEMPORARY PALAEOHYDROLOGY

Contributions from contemporary palaeohydrology derive from establishing: (1) quantitative palaeohydrological indicators of global change and improving the precision of dating fluvial deposits; both required to obtain high resolution paleoclimatic and environmental records from stratigraphic sequences; (2) potential responses of palaeohydrological systems to large-amplitude (millennial scale), rapid (decadal to centennial) global change, demonstrating the utility of paleohydrology in determining high-resolution global change records. Key palaeohydrological research investigations are based upon sediment-based research and process-based studies in addition to analysis of landform assemblages. Sediment-based interpretations from studies of alluvial plain sequences, demonstrate changes in the discharge-load relationships over long time periods (0.1-1 ka), and provide sedimentary evidence of individual events, such as floods. The other trend, of process-based palaeohydrological research, focuses on studies which provide better understanding of components of the hydrological cycle including the water balance components, river discharge (mean and flood discharge), surface-groundwater exchange, sediment transport, and rates of erosion and sedimentation in channels and on floodplains. Analysis of basin components, including palaeochannels, lakes and vegetation (pollen), provide the data necessary to estimate hydrological fluxes and to develop models of the hydrological cycle and water balance of the past. Palaeoflood hydrology provides a good example of synergy between sediment and process based research, together with modelling of flood hydraulic conditions. Contributions to global change science (Gregory and Benito, 2003) require further palaeohydrological quantification to improve understanding of relations between climate and hydrological changes as a basis for application in climate models.