"Flood Forecasting - A Whole New Level of Guidance"

2012 Association of State Floodplain Managers Annual Conference, San Antonio, TX
May 22, 2012
By Michael McMahon

A transition is occurring in flood warning that is changing the way agencies think about their actions and the time it takes to warn. Advances in Quantitative Precipitation Forecasting (QPF), both in the public and private sector, combined with the ability to rapidly/accurately process Doppler Radar information, has enabled floodplain managers and their first responders with the increasing ability to be proactive rather than reactive in regards to flooding concerns. This change is providing an increase in time-to-warn, while decreasing ongoing costs related to the care and maintenance of traditional warning systems.

One of the first rules of flooding warning is, "Do not overwarn or do not underwarn." Here-to-fore confidence levels in QPF have not been strong enough to overcome the established methodologies for flood warning. Improved techniques/model capabilities and a greater emphasis on the need for a more accurate QPF have driven federal agencies (i.e. HPC, AHPS, RFC's), as well as private sector meteorologists to concentrate their efforts on producing a far better QPF. While these efforts have greatly increased the time-to-warn, they do so at a cost-to-benefit ratio approaching 1/100.

Additionally, advances in the processing of Doppler Radar information in real-time for input into in-situ hydrologic modeling have enabled agencies to increase their spatial and temporal understanding of an ongoing precipitation event, while reducing their start-up and maintenance costs for their terrestrial gage networks. The processing of Doppler Radar information has become efficient and reliable enough to provide up to a 50 percent reduction in the number of terrestrial gages that are necessary to provide sufficient coverage. This discussion will address these topics, as well as a look into what future technologies such as Dual Pol Doppler and GOES-R, S and T will bring to flood warning.