NOAA’s National Weather Service National River Forecast Verification System NOAA Science Advisory Board Meeting July 16, 2003 Gary Carter Director, Office

NOAA’s National Weather Service

National River Forecast Verification System

NOAA Science Advisory Board Meeting

July 16, 2003

Gary CarterDirector, Office of Hydrologic Development


Verification of River Stage Forecasts Verification of River Stage Forecasts

Started April 2001 for 194 locations nationwideStarted April 2001 for 194 locations nationwideData archived at each River Forecast Center Data archived at each River Forecast Center Mean Absolute Error (MAE) results stratified by:Mean Absolute Error (MAE) results stratified by:

Flow LevelFlow Level - above and below flood stage - above and below flood stage Forecast Lead TimeForecast Lead Time - 6 to 72 hours - 6 to 72 hours

River Response to RainfallRiver Response to Rainfall - fast, intermediate, - fast, intermediate, and slowand slow

Note: more robust verification methodology will be Note: more robust verification methodology will be introduced, data points are not statistically independent introduced, data points are not statistically independent


River Forecasting Challenges: River Forecasting Challenges: Conceptual Catchment RepresentationConceptual Catchment Representation

Evapo-transpiration

Rainfall

Infiltration

Soil moisture storage

Groundwater storage

Fast flow

Percolation

Slow flow

Base flow

Total flow


Above and Below Flood StageAbove and Below Flood StageSample Sizes Sample Sizes

April 2001 to March 2003April 2001 to March 2003

020000400006000080000

100000120000140000160000180000200000

Day 1Below

Day 1Above

Day 2Below

Day 2Above

Day 3Below

Day 3Above

Fast (<24 hrs)

Medium (24 to 60hrs)Slow (> 60hrs)


Below Flood Stage ForecastsBelow Flood Stage ForecastsMean Absolute Error (feet) Mean Absolute Error (feet)


0

0.5

1

1.5

2

2.5

3

3.5

Day 1 Day 2 Day 3

Fast (<24 hrs)



Above Flood Stage ForecastsAbove Flood Stage ForecastsMean Absolute Error (feet) Mean Absolute Error (feet)


0

0.5

1

1.5

2

2.5

3

3.5

Day 1 Day 2 Day 3

Fast (<24 hrs)



Summary of Verification IssuesSummary of Verification Issues

MAEs range from about MAEs range from about 0.2 to 2.5 feet0.2 to 2.5 feet and generally and generally increase with forecast lead timeincrease with forecast lead timeNWS River Forecast System NWS River Forecast System performs well for locations performs well for locations below flood stage and for Slow riversbelow flood stage and for Slow rivers with 3 days, or with 3 days, or more, delay between heavy rainfall and the crest (e.g., more, delay between heavy rainfall and the crest (e.g., Ohio River at Evansville, IL)Ohio River at Evansville, IL)Intermediate Rivers with 1 - 2 days between heavy Intermediate Rivers with 1 - 2 days between heavy rainfall and crest (e.g., Russian River at Guerneville, rainfall and crest (e.g., Russian River at Guerneville, CA) CA) are difficult to forecast above flood stageare difficult to forecast above flood stage: : investigate impacts of improved quantitative investigate impacts of improved quantitative precipitation forecasts and deploy high resolution precipitation forecasts and deploy high resolution hydrologic models hydrologic models


On-going ProjectsOn-going Projects

Water Predictionsfor

Life Decisions

Probabilistic River Forecast Verification Methodology - Probabilistic River Forecast Verification Methodology - University of ArizonaUniversity of Arizona

Evaluation and Enhancement of River Forecast Evaluation and Enhancement of River Forecast Verification Procedures – Verification Procedures – NWS PhD DissertationNWS PhD Dissertation

Documents

NOAA’s National Weather Service National River Forecast Verification System NOAA Science Advisory Board Meeting July 16, 2003 Gary Carter Director, Office