Toward estimating the probability of flood severity over the United States

The characterization of flood severity is of overriding importance to floods monitoring, to support the flood hazard mitigation process and to evaluate operational hydrologic models. Currently flood severity levels (warning, minor, moderate, major) are defined only at gauged locations. This contribution presents the estimation of these levels at ungauged locations over the Conterminous United States (CONUS). An innovative approach to estimate probabilistic instead of deterministic flood stage values was developed quantifying the relation between the flood stage and soil characteristics, land cover/land use, geomorphology and precipitation climatology. Data from the CONUS-wide stream gauge network of the United States' Geological Survey (USGS) were used in the analysis. They are implemented in the FLASH distributed hydrologic modeling approach to assess the impending severity of flash flooding. More applications to the characterization of uncertainty in a hydrologic modeling system and probabilistic forecasting framework at ungauged locations will be presented.