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
DHM-Frequency Surface Response Supporting Flash Flooding Decisions Making
Edward Clark – Senior HydrologistNOAA’s Colorado Basin River Forecast Center
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.
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
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.
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
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
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.
Discharge
Fre
quen
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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…
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
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DHM-FSR Post- Processor
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
Frequency Discharge ExampleDischarge FrequencyDischarge
Non Exceedance Percentage
Frequency Surface Flow ExampleSurface Flow FrequencySurface Flow
Non Exceedence Percentage
Dissemination: CBRFC Webpage
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.
Dissemination: AWIPS D2D Prototype
Gridded Discharge
Discharge Frequency
MPE Derived 1-hr QPE
Surface Flow Frequency
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.
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.
Cell value time series -- Are Hydrologic Conditions getting better or worse?
Time (hr)
1 -
fre
qu
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1 -
fre
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Time (hr)
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.
