Hydrologic Outlook for the Pacific Northwest

Andy Wood

andDennis P. Lettenmaier

Department of Civil and Environmental Engineering

for Washington Water Outlook Workshop

UW Climate Impacts Group

March 21, 2005

Presentation Outline

1. Introduction: UW Experimental Hydrologic

Forecasting System

2. Water Year 2005 Assessment

Sn

ow w

ater

con

ten

t on

Ap

ril

1

April to August runoff

McLean, D.A., 1948 Western Snow Conf.

SNOTEL Network

Introduction: Hydrologic prediction

PNW

Technical Advances related to Hydrologic Forecasting

1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s

snow survey / graphical forecasts /

index methods / i.e., regression

computing in water

resources

aerial snow

surveys

SNOTEL network

ESP method

snow cats

conceptualhydrologic

models

Introduction: Hydrologic prediction and ESP

NWS River Forecast Center (RFC) approach:

rainfall-runoff modeling(i.e., NWS River Forecast System,

Anderson, 1973 offspring of Stanford Watershed Model, Crawford & Linsley, 1966)

Ensemble Streamflow Prediction (ESP)

• used for shorter lead predictions;• ~ used for longer lead predictions

Currently, some western RFCs and NRCS coordinate their seasonal forecasts, using mostly statistical methods.

ICsSpin-up Forecast

obs

recently observedmeteorological data

ensemble of met. datato generate forecast

ESP forecast

hydrologicstate

Technical Advances related to Hydrologic Forecasting

1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s

snow survey / graphical forecasts /

index methods / i.e., regression

computing in water

resources

satelliteimagery

aerial snow

surveys desktopcomputing

SNOTEL network

ESP method

ENSO / seasonal climate

forecasts

snow catsInternet / real-time

data

conceptualhydrologic

models

physicalhydrologic

models

Introduction: Experimental Hydrologic Forecasting

Introduction: Experimental Hydrologic Forecasting

Soil MoistureInitial

Condition

SnowpackInitial Condition

Introduction: Merging of SNOTEL obs with model SWE

The pattern of observed SWE values, which are merged with the forecast initial conditions, was in good agreement with the VIC simulated snow state.

The PNW currently has very low snowpack, while the Southwest and California have record high snowpacks.

Introduction: Experimental Hydrologic Forecasting

targeted statistics e.g., runoff volumes

monthly hydrographs

streamflowforecastlocations

Introduction: UW Experimental Hydrologic Forecasting

SWE Soil MoistureRunoffPrecip Temp

Mar-05

Apr-05

May-05

Presentation Outline

1. Introduction: UW Experimental Hydrologic Forecasting

System

2. Water Year 2005 Assessment

WY2005, Dec. 1 hydrologic conditions

WY2005, Dec. 1 hydrologic conditions

WY2005, Jan. 1 hydrologic conditions

WY2005, Feb. 1 hydrologic conditions

WY2005, Mar. 1 hydrologic conditions

3/15 ESP fcst: Basin Average Water Balance

The following series of results are for a March 15 ESP forecast, based on 1960-99 climate traces, compared with climatology

forecast distribution

max

0.75median0.25

min

spinup

3/15 ESP fcst: WY2005 vs. WY1977 Precip, Temp

Puget Sound Drainage Basin

How does the WY2005 current year compare to WY1977?

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 SM, SWE

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 Runoff

WY2005

WY1977

Puget Sound Drainage Basin

Apr-Sep% of avgmax 800.75 600.50 540.25 49min 45

3/15 ESP fcst: WY2005 vs. WY1977 Precip, Temp

BC portion of Columbia R. Basin

How does the WY2005 current year compare to WY1977?

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 SM, SWE

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 Runoff

WY2005

WY1977

BC portion of Columbia R. Basin

Apr-Sep% of avgmax 950.75 830.50 780.25 74min 64

3/15 ESP fcst: WY2005 vs. WY1977 Precip, Temp

Columbia R. basin upstream of The

Dalles, OR

How does the WY2005 current year compare to WY1977?

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 SM, SWE

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 Runoff

Columbia R. basin upstream of The

Dalles, OR WY2005

WY1977

Apr-Sep% of avgmax 880.75 730.50 690.25 65min 55

Conclusions

Puget Sound regional runoff will be in the lowest quartile: 50% chance of between 49 - 60 % of normal

Columbia R. basin in slightly better shape, but still in lowest quartile: median runoff forecast is 69% of normal

Some other areas, such as the Yakima Basin, are drier than Puget Sound (39-46% of normal runoff)

This has been a rough year for forecasters!

Questions?

website:

www.hydro.washington.edu / Lettenmaier / Projects / fcst /

Introduction: Experimental Hydrologic Forecasting

VIC model runoff is routed to streamflow gages, and verified against observations

Introduction: Seasonal Climate Prediction

e.g., precipitation

3/15 ESP fcst: WY2005 vs. WY1977 Precip, Temp

BC portion of Columbia R. Basin

How does the WY2005 current year compare to WY1977?

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 SM, SWE

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 Runoff

WY2005

WY1977

Snake R. Basin

Apr-Sep% of avgmax 900.75 710.50 620.25 57min 49

3/15 ESP fcst: WY2005 vs. WY1977 Precip, Temp

Yakima R. Basin near

Parker, WA

How does the WY2005 current year compare to WY1977?

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 SM, SWE

WY2005WY1977

3/15 ESP fcst: WY2005 vs. WY1977 Runoff

WY2005

WY1977

Yakima R. Basin near Parker, WA

Apr-Sep% of avgmax 610.75 460.50 410.25 39min 31