distributed hydrologic model-threshold frequency (dhm-tf)
DESCRIPTION
Distributed Hydrologic Model-Threshold Frequency (DHM-TF) . Reggina Cabrera NOAA/National Weather Service Eastern Region [email protected]. Tools. FFPI FFMPA DHM-TF. Concepts. NWS defines a flash flood as a flood that occurs within 6-hours of the causative event (rainfall) - PowerPoint PPT PresentationTRANSCRIPT
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Distributed Hydrologic Model-Threshold Frequency
(DHM-TF)
Reggina CabreraNOAA/National Weather
ServiceEastern Region
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Tools
2
FFPI FFMP DHM-TF
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FFPI FFMPA DHM-TF
FFPI
• Shows you areas that you should be concerned, where flash flooding could occur. It is static
FFMPA
• Monitors areas where current/future rainfall might prompt a warning. It is dynamic
DHM-TF
• Shows you severity of impacts which you might communicate to the public. It is dynamic
3
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ConceptsNWS defines a flash flood as a flood that
occurs within 6-hours of the causative event (rainfall)
FFG is the depth of runoff over a given duration required to cause flooding in small
streams. FFG procedures use regionally derived threshold at at ungaged locations.
These are flows that exceed bankful just enough to cause damage.
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DHM-TF Modeling ApproachObjective Improve flash flood forecast at ungaged locations by using a distributed hydrologic model with a frequency post-processor.
Advantages:
The proposed approach models flow and characterizes flood severity at ungaged locations
It aids in the forecaster’s warning decisions
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DHM-TF Modeling Approach
Spatial and temporal scales that are more commensurate with flash flooding
Distributed models provide a framework for forecasting flashy
events that occur at higher spatial and temporal resolutions than the lumped
models used at the River Forecast Centers
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Rainfall input data MPE- Multisensor Precipitation
Estimator (observations at 4 km resolution, hourly)
HPE- High Resolution Precipitation Estimator ( observations at 1 km resolution, hourly )
HPN- High Resolution Precipitation Nowcaster (forecasts at 4 km resolution, hourly)
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The Process DHM produces gridded flow forecasts
Gridded frequency (return period) forecasts are derived based on historical simulations
Historical Simulations Conducted with DHM
Same type of forcing data used as in forecast simulations to derive statistical parameters
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Modeling Flash Floods Model Output
Map of modeled flood frequencies
NWS/OHD Implementation Sacramento model with kinematic routing Any model can be used that reasonably represents
flow distribution
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Statistical Component
Gridded Flow Forecasts
Gridded Frequency Forecasts
Post-Processor Statistical
characteristics derived from
historical simulations
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Maximum DHM-TF Return Period Values (Years) for August 9th Flash Flood Event(10Z 8/9/07 through 06Z 8/10/07)
Standard Cell-to-Cell Routing Local Routing
*Blue wave symbols indicate spotter-reported flash flood events
• Overall, good match between areas of high DHM-TF return periods and spotter-reported events (wave symbols)
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Girty’s Run DHM-TF return periods (years)18Z-21Z August 9th 2007
Standard cell-to-cell routing method used
• Return period values appear low given severity of flash flood event over Millvale
*Blue wave symbols indicate spotter-reported flash flood events
Return Period (years)20Z 8/9/07
Return Period (years)21Z 8/9/07
Return Period (years)18Z 8/9/07
Return Period (years)19Z 8/9/07
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Girty’s Run DHM-TF return periods (years)18Z-21Z August 9th 2007
Local routing (unconnected) method used
• Return period values appear low given severity of flash flood event over Millvale
*Blue wave symbols indicate spotter-reported flash flood events
Return Period (years)20Z 8/9/07
Return Period (years)21Z 8/9/07
Return Period (years)18Z 8/9/07
Return Period (years)19Z 8/9/07
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Rea
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Buffalo WFO Flash Flood Warning Buffalo (Blue Outline)DHM-TF Return Periods (years) for 13Z on 8/10/09
Large DHM-TF return periods overlap with area of flash flood warning
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Evaluation
Real-time Verification: Limited qualitative analysis has demonstrated that increased DHM-TF return periods generally match areas of heavy rain and flash flooding, while low DHM-TF return periods generally match non-flooded areas.