Moving toward optimum use of gridded precipitation forcings in hydrologic modeling

Among the major challenges facing National Weather Service (NWS) hydrologists in the next few years is the development of a high-spatial resolution, gridded hourly precipitation record spanning multiple decades, suitable for calibration of distributed hydrologic models and statistical conditioning of ensemble hydrologic model input. The record should feature a grid mesh length ≤ 4 km and no more than a 1-hour time increment. The available input includes data from an observation network that has changed dramatically since 1960, and an expanding variety of sensor platforms (rain gauge, radar, satellite). Analysis frameworks, such as statistical interpolation and physical-dynamical reanalysis, continue to evolve. A major challenge is accounting for time-dependent biases introduced solely by changes in the observing network.

A discussion of these issues was initiated at the 2010 AMS annual meeting. Approaches to constructing precipitation, temperature, and radiation balance Analyses of Record are under discussion among several NWS offices. Finally, tests of different approaches to precipitation and temperature reanalysis have been undertaken at some NWS River Forecast Centers, and the impacts on calibration of hydrologic models has been evaluated. This presentation will feature a summary of the many methods that have been applied to retrospective and real-time precipitation analysis, including recent advances in radar precipitation estimation, and the suitability of the approaches to hydrologic applications. We expect to stimulate further discussion on how the final goal of a multi-decade gridded precipitation dataset might be achieved, given the wide variety of options for input observations and estimates and analysis techniques.