Impacts of hydrological variability and change on water resources

Dennis P. LettenmaierDepartment of Civil and Environmental Engineering

University of Washington

for presentation at

Fifth IHP/IAHS George Kovacs Colloquium

UNESCO, Paris

2 June 2000

Outline of this talk1) Approach to long-lead hydrological

forecasts utilizing resampling anddownscaled climate models (ColumbiaRiver example)

2) Evolving approach to forecasting U.S.soil moisture and streamflow usingensemble climate forecasts

3) Assessment of sensitivity of globalrivers to climate change, and detailedexample for Columbia River basin

Modeling the Connections Between Climate and Streamflow

Currently Modeled US Basins

1 Northwest 5 Rio Grande 10 Upper Mississippi2 California 6 Missouri 11 Lower Mississippi3 Great Basin 7 Arkansas-Red 12 Ohio4 Colorado 8 Gulf 13 East Coast

9 Great Lakes

Long-LeadClimate Forecast

ENSO

PDO

Run Initialized Hydrologic Model

Ensemble StreamflowForecast

Select Met Data Ensemble fromHistoric Record Associated with

Forecast Climate Category

Schematic for Forecasting Experiments Using Resampled Observed Data

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Time Line for 12-month Lead Time Retrospective Forecasts

Climate Forecast

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Estimated Initial Conditions

ForecastEnsemble

Lead time = 12 months

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Columbia River Streamflow Forecast at The Dalles for 2001

Highest Simulation (1948-1997)

Lowest Simulation (1948-1997)

Cool PDO/ENSO Neut.Ensemble

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Columbia River Streamflow Forecast at The Dalles for 2000

Global Climate Models

Regional Climate Models

Hydrology Models

WaterResources

Models

Overview of Streamflow Forecasting Schemes Using Climate Models

water demand

streamflowTemp. Precip. winddownscaling

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Repeating 1960 Observed Temp and Precip Time Series with Nov-April Replaced by MM5 Forecasts

MM5 Sim

Constructing the Hydrology Model Driving Data Using a Normal SST Nov-Apr Climate Forecast

MM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 SimMM5 Sim

24 MM5 Forecasts

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(CFS

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Control(observed Nov-Apr’s)

RCM(raw climate simulationsfor Nov-Apr’s)

Test Simulations for the Columbia River at The Dalles

Mean

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Simple Bias Correction Used in MM5 Experiments(Nov-Mar Ensembles inserted in repeating 1960)

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Quantile Mapping Bias Correction

Mean

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Kanawha River Basin Simulations Using Observed Data and Bias Corrected GCM Output

Observations

Bias-Corrected GCM

Downscaled GSM forecast ensembles compared to historical climatological bounds

1 Ohio 3 Delaware 4 Alabama-Coosa-Tallapoosa2 Potomac 5 Apalachicola-Chattahoochee-Flint

Current Streamflow Forecast Basins

Current Streamflow Forecast Basins

Climate Scenarios

Transient GCM Simulations for Increasing CO2 and Aerosols

AdjustmentsTo ObservedMeteorology

Delta Precip,Temp

HydrologicModel (VIC)

Natural Streamflow

ReservoirModel (ColSim)

DamReleases,Regulated

Streamflow

PerformanceMeasures

Reliability of System Objectives

CORRA

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System Objective

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ColSim Reliability of System Objectives