dhm-frequency surface response supporting flash flooding decisions making
DESCRIPTION
DHM-Frequency Surface Response Supporting Flash Flooding Decisions Making. Edward Clark – Senior Hydrologist NOAA’s Colorado Basin River Forecast Center. Outline. Background and Concept for the Distributed Hydrologic Model – Frequency Surface Response (DHM-FSR) Examples from 2008 - PowerPoint PPT PresentationTRANSCRIPT
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DHM-Frequency Surface Response Supporting Flash Flooding Decisions Making
Edward Clark – Senior HydrologistNOAA’s Colorado Basin River Forecast Center
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Outline• Background and Concept for the Distributed Hydrologic Model – Frequency Surface Response (DHM-FSR)
• Examples from 2008
• Display and Dissemination methods
• Incorporation into the Flash Flood CONOPS and improvements over the existing RFC Flash Flood support.
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Background
CBRFC began working with the NWS Distributed Hydrologic Model(s) in 2005 with three main applications/areas:
• Incorporation of Distributed Model output time-Series into NWSRFS
• Gridded Soil Moisture products.
• Flash Flood application – DHM-FSR
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Concept
1. Run a calibrated version of the National Weather Service (NWS) Hydrology Lab -- Research Distributed Hydrologic Model (HL-RDHM) to model basins response quantified precipitation estimates and forecasts.
2. Normalize each cell’s discharge (channel flow) and surface flow (non-channelized flow) by comparing it to a historic distribution of hourly values.
3. Produce and disseminate gridded maps of the normalized response in real-time.
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Distributed Hydrologic Model
Each modeling element (4-km x 4-km Grid Cell) is characterized by discrete:
• Soils Data• Vegetation• Land Cover/Use• Slope• Aspect
Discharge
Distributed Sacramento Soil Moisture Accounting Model
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What types of flooding occur within the CBRFC bounds?
Channel Flooding : Defined by HL-RDHM Discharge
Sheet flooding is flooding caused by comparatively shallow water flowing over a wide, relatively flat area which typically does not have the appearance of a well defined watercourse…
Sheet Flooding: Defined by HL-RDHM SurfaceFlow
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Why a normalization?
• Communicate the magnitude of the response without the flow/stage relationship that can be developed at a stream gage.
• Necessary to adjust for the size of the drainage area above the grid cell – response from small streams and large rivers.
• Make the current grid states meaningful to the forecaster.
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Discharge
Fre
quen
cy
00z, Jan 1st, 2004
23z, Oct. 31th, 2008
Modeled Historic Distribution
Dec 04 – Mar 05: Large Scale Synoptic Events
2006 Monsoon season – record flooding
2007 Monsoon season
Objectively quantify an events response in relationship to previous responses.
Each hour’s gridded simulation…
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Non-Exceedance
values
Grid of Discharge or Surface Flow
Operational Concept
CriticalThreshold
“The current discharge is in the top 5% of historical responses…”
DischargeOrSurfaceFlow
Fre
quen
cy
DHM-FSR Post- Processor
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Operational Run-times
Run twice each hour:• 15 minutes past – first radar scans• 45 minutes past – initial ALERT gage reports and radar
• Initialized with (current – 12-hour) model states• Runs (+) 6-hrs for response to QPE and QPF
-12-hr Model RunModel Run
Current Hour
QPE QPF
+6-hr
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Frequency Discharge ExampleDischarge FrequencyDischarge
Non Exceedance Percentage
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Frequency Surface Flow ExampleSurface Flow FrequencySurface Flow
Non Exceedence Percentage
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Dissemination: CBRFC Webpage
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Dissemination: CBRFC Webpage
Advantages• Utilizes Google Maps
imagery for reference. • Portable – relies only
on a web browser. • Can display any
period of interest (useful for retrospective analysis.)
Disadvantages:• Not in the WFO
Forecaster’s toolbox.• Need to process xmrg
format to geographic ascii grid.
• Lag in updating due to conversion and firewall issues.
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Dissemination: AWIPS D2D Prototype
Gridded Discharge
Discharge Frequency
MPE Derived 1-hr QPE
Surface Flow Frequency
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Dissemination: AWIPS D2D Prototype
Advantages:• Familiar tool to the
Forecast• Simple conversion from
xmrg to grib format (no geographic transform).
• Rapid updating (remains within AWIPS.)
• Existing loop and query tools.
Disadvantages:• Background images not
as robust as Google maps interface.
• Limited number of grids ~3-5 days.
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Supporting the Flash Flood Watch/Warning Process
• Not designed to replace FFMP – WFO is still expected to “warn on the rain.”
• Identify specific regions of higher impacts.• Answer questions about the duration of flash flooding. • In time, incorporate the short term QPF to better
estimate future response.
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Cell value time series -- Are Hydrologic Conditions getting better or worse?
Time (hr)
1 -
fre
qu
en
cy
1 -
fre
qu
en
cy
Time (hr)
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Enhancements over Existing RFC Flash Flood Products
• Incorporates soil, land use, slope and vegetation cover into a calibrated model.
• Adds connectivity to route multiple headwater basin cells into downstream cells.
• Remembers the carryover in soil moisture states from previous events.
• Values are relative to previous response. WFO’s can develop knowledge of their local regional problem areas and set critical non-exceedence values.