Example: Application of the Variable Infiltration Capacity model to climate impact assessment in the Colorado River basin

Dennis P. LettenmaierDepartment of Civil and Environmental Engineering

University of Washington

for presentation at

Dividing the waters: Science for Judges Workshop IV

Workshop on Climate Change Modeling: General Circulation Models and Hydrometeorologic Models

Hotel BoulderadoBoulder, Colorado

May 13 – 15, 2007

Outline of this talk

1) Climate variability and change context2) Prediction and assessment approach3) Hydrology and water management

implications for Colorado River basin -- Accelerated Climate Prediction Initiative (ACPI)

4) Postmortem – Milly et al (2005); Seager et al (2007); Christensen and Lettenmaier (2007)

1) Climate variability and change context

Temperature trends in the PNW over the instrumental record

• Almost every station shows warming (filled circles)

• Urbanization not a major source of warming

Trends in timing of spring snowmelt (1948-2000)

Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan

+20d later–20d earlier

Source: Mote et al, 2005

Trends in snowpack

2) Prediction and assessment approach

Climate Scenarios

Global climate simulations, next ~100 yrs

Downscaling

Delta Precip,Temp

HydrologicModel (VIC)

Natural Streamflow

ReservoirModel

DamReleases,Regulated

Streamflow

PerformanceMeasures

Reliability of System Objectives

ReservoirModel

Hydrology Model

Coupled Land-Atmosphere-Ocean General Circulation

Model

Accelerated Climate Prediction Initiative (ACPI) – NCAR/DOE Parallel Climate Model (PCM) grid over western U.S.

Bias Correction and Downscaling Approach

climate model scenariometeorological outputs

hydrologic model inputs

snowpackrunoffstreamflow

• 1/8-1/4 degree resolution• daily P, Tmin, Tmax

•2.8 (T42)/0.5 degree resolution•monthly total P, avg. T

Bias Correction

from NCDC observations

from PCM historical runraw climate scenario

bias-corrected climate scenario

month mmonth m

Note: future scenario temperature trend (relative to control run) removed before, and replaced after, bias-correction step.

Downscaling

observed mean fields

(1/8-1/4 degree)

monthly PCManomaly (T42)

VIC-scale monthly simulation

interpolated to VIC scale

Dam Operations in ColSim

Storage Dams

Run-of-River Dams

0

100000

200000

300000

400000

500000

600000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Avg

Str

eam

flow

(cf

s)

0

100000

200000

300000

400000

500000

600000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Avg

Str

eam

flow

(cf

s) Virgin Regulated

Flow In=Flow out + Energy

H

Inflow

Run of River Reservoirs (inflow=outflow + energy)

Inflow

Inflow

Inflow

Inflow

Inflow

Storage ReservoirsReleases Depend on:•Storage and Inflow•Rule Curves (streamflow forecasts)•Flood Control Requirements•Energy Requirements•Minimum Flow Requirements•System Flow Requirements

System Checkpoint

Consumptive use

Consumptive use

Inflow +

ColSim

3) Accelerated Climate Prediction Initiative (ACPI)

GCM grid mesh over western U.S. (NCAR/DOE Parallel Climate Model at ~ 2.8 degrees lat-long)

Climate Change Scenarios

Historical B06.22 (greenhouse CO2+aerosols forcing) 1870-2000

Climate Control B06.45 (CO2+aerosols at 1995 levels) 1995-2048

Climate Change B06.44 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.46 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.47 (BAU6, future scenario forcing) 1995-2099

Climate Control B06.45 derived-subset 1995-2015

Climate Change B06.44 derived-subset 2040-2060

PCM Simulations (~ 3 degrees lat-long)

PNNL Regional Climate Model (RCM) Simulations (~ ¾ degree lat-long)

Future streamflows

• 3 ensembles averaged

• summarized into 3 periods;» Period 1 2010 - 2039

» Period 2 2040 - 2070

» Period 3 2070 - 2098

4a) Hydrology and water management implications: Colorado River basin

Timeseries Annual Average

Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098

hist. avg.

ctrl. avg.

PCM Projected Colorado R. Temperature

hist. avg.

ctrl. avg.

PCM Projected Colorado R. Precipitation

Timeseries Annual Average

Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098

Annual Average Hydrograph

Simulated Historic (1950-1999) Period 1 (2010-2039)Control (static 1995 climate) Period 2 (2040-2069)

Period 3 (2070-2098)

Projected Spatial Change in Runoff

90 %86 %82 %83 %

April 1 Snow Water Equivalent

Natural Flow at Lee Ferry, AZ

Currently used 16.3 BCM

allocated20.3 BCM

Storage ReservoirsRun of River Reservoirs

CRRM

• Basin storage aggregated into 4 storage reservoirs

– Lake Powell and Lake Mead have 85% of basin storage

• Reservoir evaporation = f(reservoir surface area, mean monthly temperature)

• Hydropower = f(release, reservoir elevation)

• Monthly timestep

• Historic Streamflows to Validate

• Projected Inflows to assess future performance of system

Water Management Model (CRRM)

• Multi Species Conservation Program year 2000 demands– upper basin 5.4 BCM

– lower basin 9.3 BCM

– Mexico 1.8 BCM

• Minimum Annual Release from Glen Canyon Dam of 10.8 BCM

• Minimum Annual Release from Imperial Dam of 1.8 BCM

Total Basin Storage

Annual Releases to the Lower Basin

target release

Annual Releases to Mexico

target release

Annual Hydropower Production

Uncontrolled Spills

Deliveries to CAP & MWD

Postmortem: Christensen and Lettenmaier (HESSD, 2007) – multimodel ensemble analysis with 11 IPCC

AR4 models (downscaled as in C&L, 2004)

Magnitude and Consistency of Model-Projected Changesin Annual Runoff by Water Resources Region, 2041-2060

Median change in annual runoff from 24 numerical experiments (color scale)and fraction of 24 experiments producing common direction of change (inset numerical values).

+25%

+10%

+5%

+2%

-2%

-5%

-10%

-25%

Dec

reas

eIn

crea

se

(After Milly, P.C.D., K.A. Dunne, A.V. Vecchia, Global pattern of trends in streamflow andwater availability in a changing climate, Nature, 438, 347-350, 2005.)

96%

75%67%

62%87%

87%

71%

67%62%

58%

67%

62%58%

67%100%

from Seager et al, Science Express, 2007

5) Conclusions and Comparative analysis

• 1) Columbia River reservoir system primarily provides within-year storage (total storage/mean flow ~ 0.3). California is intermediate (~ 0.3), Colorado is an over-year system (~4)

• 2) Climate sensitivities in Columbia basin are dominated by seasonality shifts in streamflow, and may even be beneficial for hydropower. However, fish flow targets would be difficult to meet under altered climate, and mitigation by altered operation is essentially impossible.

• 3) California system operation is dominated by water supply (mostly ag), reliability of which would be reduced significantly by a combination of seaonality shifts and reduced (annual) volumes. Partial mitigation by altered operations is possible, but complicated by flood issues.

• 4) Colorado system is sensitive primarily to annual streamflow volumes. Low runoff ratio makes the system highly sensitive to modest changes in precipitation (in winter, esp, in headwaters). Sensitivity to altered operations is modest, and mitigation possibilities by increased storage are nil (even if otherwise feasible).