This Technical Committee on Hydrologic Uncertainty seeks to improve how uncertainty is evaluated and measured by scientists in the Hydrology section of AGU, and to improve how uncertainty is communicated within and beyond the hydrology section. The technical committee maintains a log site at http://aguhu.blogspot.com/ for communication and evolution of scientific sessions. Hydrologists use uncertainty concepts and measures in many ways, from testing theories against data to providing regulators with defensible quantification of uncertainties associated with sometimes controversial environmental problems (e.g., sustainability, integrated water resources management, climate impacts, carbon sequestration, hydrofracking, and waste disposition). Issues of interest include how uncertainties (in data and model structures, parameters, and driving forces) are represented, evaluated, and reduced; uncertainty quantification in risk analysis and decision support; and how legal structures do and do not integrate the reality of uncertainty. Of interest are probabilistic and non-probabilistic metrics used to evaluate model responses, judge models against data, rank alternative models and test hypotheses; sensitivity analyses used to unravel sources of uncertainty; data collection strategies optimized for uncertainty reduction; and novel ideas not yet considered. As uncertainty is a cross-cutting issue, the Hydrology Section Uncertainty Technical Committee coordinates with other sections of AGU to include the notion of uncertainty in their research fields. This interdisciplinary and quantitative focus provides fruitful opportunities for conducting collaborative research with broader funding opportunities. It is one of the critical missions of the committee to foster interdisciplinary research for uncertainty analysis and to use uncertainty analysis as a vital tool for advanced understanding and bridging multiple disciplines.