Frontier Lecture in Hydrological Science: Runoff Generation in Gauged and Ungauged Watersheds: Status and Future

The IAHS Prediction in Ungauged Basins (PUB) Initiative offers an unprecedented opportunity for process hydrologists, modelers and theoreticians to work together on a common problem: reduction of predictive uncertainty. While this topic has been addressed in recent years in the watershed modeling community, only recently have experimentalists begun to explore how conceptual understanding of basin behavior may be used to structure (and reject) new models, be used as soft data in multi-criteria model calibration and to narrow model parameter ranges. This paper attempts to distill the key concepts of runoff generation in an attempt to whittle-down the myriad complexities of hillslope behavior often reported toward defining emergent properties at the basin scale. It is argued that future process studies should be comparative in nature and recognize the limitations to inference from current field practice. New data sources and process ideas may form new measures of model acceptability, as the community moves away from calibration-reliant model schemes to more process-representative descriptions applicable in ungauged basins.