TOWARDS A NATIONAL HYDROLOGIC MODEL: OVERVIEW

A National Hydrologic Model (NHM) is being developed to support coordinated and robust hydrologic model development and application within the USGS. The NHM addresses four important aspects which must be considered for a relevant, comprehensive and successful hydrologic-modeling program: 1) Development of technology which makes the best available data readily accessible to modelers; 2) Relevant research and developments in the field of hydrologic modeling to adapt to increasingly complex questions and take advantage of improved data sources; 3) Development of standard methods which can be applied to produce consistent and comparable hydrologic model studies; and 4) Development of a modeling archive system which provides a platform for model distribution, dissemination of results, comparability, and interoperability.

The development and calibration of model studies within the National Hydrologic Model is currently leveraging work in several pilot studies. Current project-specific tools for retrieving spatial and time-series data for climatological inputs and streamflows are being generalized to develop an intuitive, web-based user interface which can be used to provide information for modeling and decision support needs. Monthly average runoff for the period 1895 through 2009 from a National Water Balance model, based on a 4 km grid across the conterminous U.S., will be made available through the spatial data retrieval tool. The NHM will be based on the U.S. Geological Survey’s Precipitation Runoff Modeling System (PRMS), which is a deterministic, distributed-parameter hydrologic model that runs on a daily time step and has a modular-design. Research and development of the PRMS model will include evolving landscapes and dynamic parameters, uncertainty analysis and parameter estimation techniques, simulating frozen ground and glacier dynamics, landscape recovery following wildfires, and simulating stream temperature. The initial NHM will use a coarse spatial scale, with the ability to nest finer-scale models within the coarse-scale model. Several pilot studies, including the Apalachicola-Chattahoochee-Flint River study, are being used to develop the methods for creating and calibrating coarse-resolution models and nesting finer-resolution models within the coarse model.