dhm-frequency surface response supporting flash flooding decisions making

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

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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

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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

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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.

Questions

Grids: http://www.cbrfc.noaa.gov/gmap/gmap.php

Contact:Edward.Clark@noaa.gov