Dennis P. Lettenmaier

JISAO Center for Science in the Earth System Climate Impacts Group

and Department of Civil and Environmental EngineeringUniversity of Washington

April, 2003

A Brief History of Climate Change Sensitivity Work

Hydrology, water resources, and climate

• Hydrologists and water resources engineers have always had to deal with climate, it wasn’t just “discovered”

• But, the classical assumption is equivalent to statistical stationarity, “the future will resemble the past”

• Unfortunately, the future may not be like the past, which greatly complicates planning

Natural Flow at Lee Ferry, AZ

Currently used

16.3 BCM

allocated20.3 BCM

Evolution of interest in climate change in hydrology

• ~1977 NAS/NRC report (various papers, basically said “we know how to deal with this”)

• Late 1980s AAAS study (Schaake paper evaluating water balance issues, SE U.S.)

• Late 1980s EPA Reports to Congress• 1990s IPCC reports USNA (~40 papers

cited on water resources and climate)

UW interest in hydrology, water resources, and climate change

• Hydrologic sensitivities of the Sacramento-San Joaquin River basin, California, to global warming (WRR, 1990)

• Climatic sensitivity of California water resources (JWRPM, 1991)

• Sensitivity of Pacific Northwest water resources to global warming (Northwest-Environmental-Journal, 1992)

• Water resources implications of global warming: A U.S. regional perspective (Climatic-Change, 1999)

• Effects of climate change on hydrology and water resources in the Columbia River basin (JAWRA , 1999)

Effects to Snowpack

Effects to Streamflow

More Storage Less Storage

Num

ber

of S

tora

ge F

ailu

res

optimization

no optimization

U.S. Climate Change Study Basins (Lettenmaier et al. 1999)

50

60

70

80

90

100F

irm E

nerg

y

No

n-F

irm E

nerg

y

Gra

nd C

oul

ee

Re

cre

atio

n

Lo

we

r G

rani

te F

ish

Flo

w

McN

ary

Fis

h F

low

Sna

ke I

rrig

atio

n

Sna

ke R

ive

r N

avig

atio

n

Flo

od

Co

ntro

l

Current Climate

ECHAM4 2040's

HadCM2 2040's

HadCM3 2040's

PCM 2040's

VIC/ColSim 2040’s

DALLES

0

100000

200000

300000

400000

500000

600000

oct

dec

feb

apr

jun

augA

vera

ge

Flo

w (

cfs)

Base

ECHAM4

HadCM2

HadCM3

PCM

Columbia River at The Dalles

0

100000

200000

300000

400000

500000

600000

oct

dec

feb

apr

jun

aug

Ave

rag

e F

low

(cfs

)

Base

2020s

2040s

Inflow to Chester Morse Lake

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10/1

10/2

9

11/2

6

12/2

4

1/21

2/18

3/18

4/15

5/13

6/10 7/8

8/5

9/2

Infl

ow

(ac

re-f

t)

Base

2020s

2040s

Current Climate 2040 Composite Scenario

So what is the issue for this meeting?• The fundamental implications of global warming for

snowmelt dominated and transient snow rivers in the west have been well understood in the academic community for a decade or longer.

• Lots of questions about specifics, climate model uncertainty, etc. However, a) all models show there is a problem in snowmelt dominated watersheds, and b) the models are consistent with what’s been observed over the last half century or so.

• Almost all the studies are academic – few examples where the studies have been done by the water management agencies, using their own tools and models

• We are to the point where the question is no longer whether climate change is an issue, but rather how to incorporate it into the planning process (and preferably internalize it at the agency level)