Advanced Hydrologic Prediction Service (AHPS)

The National Weather Service (NWS) is the agency responsible for providing flood warnings and forecasts for the United States. This is an important job considering that floods cause $4.5 billion in damages per year and claim over 130 lives. Every day, governmental agencies, the media, private sectors, and the public depend on the NWS for its weather products and forecasting efforts. For this reason, the NWS is continually working to improve forecasting methods. The Advanced Hydrologic Prediction Service, under development since 1997, is an example of the National Weather Service's continuing efforts in working toward more accurate and timely hydrologic forecasting.

Existing NWS river stage forecasts generally provide only short-term (1-to 3-days in advance), text and tabular formatted forecast products for specific locations along a river. These forecasts are the product of applied historical weather data, stream gage data, channel cross-section data, water supply operations information and hydrologic model characteristics representing large regions.

AHPS is a step above the current forecasting methods. Applying the same hydrologic data used in current methods, AHPS also uses advanced hydrologic models with characteristics specific to local watersheds and tributaries. These advanced, localized hydrologic models increase forecast accuracy by 20% over existing models.

Not only does AHPS produce more accurate forecasts, but it provides greater-detailed products in an improved format. Many of these new forecast products are visually oriented, making them easier to understand and utilize for everyone, from the general public to planners and scientists. AHPS depicts the magnitude and probability of hydrologic events, and gives users an idea of worst case scenario situations. Finally, AHPS provides forecasts farther in advance of current methods, allowing people to gain additional time to protect themselves, their families, and their property from floods.

-	how high a river will rise
-	when a river will reach its peak flow
-	where property will be flooded
-	how long flooding will continue

Implementation of AHPS also will help the U.S. economy in general. Water managers, city officials, dam operators, farmers, commercial shippers, river navigators, and many others who depend on hydrologic forecasts will be able to operate more efficiently with the improved information. For example, information provided by AHPS will help water managers and city officials to make more informed decisions about:

-	when and where to evacuate people from areas running the risk of being flooded, potentially saving lives.
-	when personal and industrial property should be moved from potential flood areas, saving money for residents and businesses.
-	how to use reservoir storage capacity to reduce flood impacts on people and businesses downstream, potentially saving lives and benefiting the economy.

CURRENT STATUS AND FUTURE OF AHPS

DES MOINES, IOWA--The First Phase of AHPS

Following the Great Flood of 1993 in the Midwest, the Des Moines River Basin in Iowa was selected to be the first phase toward the national implementation of AHPS. In March 1997, the NWS began operating AHPS for the Des Moines Basin. Through the use of the Internet, basin residents are able to access interactive maps displaying flood forecast points. Selecting any of the flood forecast points on the map allows Internet users to obtain river stage forecast information for the point of interest. Available information includes:

-	stage hydrographs forecasting river stage for a five-day period.
-	stage, flow, and volume probability charts which detail the probability of river flow, stage, and volume exceeding particular levels over a period of several weeks.
-	90-day exceedence probability charts which detail longer-term stage and flow probabilities.
-	detailed site maps of forecast areas.
-	stage and damage tables which characterize the effects of different river stages on a community (ex. what streets can be expected to flood at a particular river stage).

It is estimated that national implementation of AHPS will save at least $200 million per year in reduced flood losses and contribute an additional $400 million a year in economic benefits to water resource users. Most importantly, it will help save lives! Nationwide implementation of AHPS is currently underway. Additional information about AHPS may be obtained on the NWS' AHPS web page.

AHPS has recently been implemented in parts of the Delaware River Basin and implementation in other portions is ongoing. Information specific to the basin can be obtained from the Middle Atlantic River Forecast Center. The Delaware River Basin Commission (DRBC), with technical input from the DRBC Flood Advisory Committee, has developed a report recommending upgrading and modernization of the basin's flood warning system. The recommendations call for development of improved flood forecast modeling, graphical forecast products, and integration of Doppler radar and Geographic Information System (GIS) technology to improve headwater flood warning. All of these products are part of the AHPS program. Implementation in the Delaware River Basin will support the national AHPS implementation goals of the NWS. Implementation of AHPS in the Middle Atlantic region is scheduled to continue through 2008.