Long-term climate and water cycle variability and change

Dennis P. LettenmaierDepartment of Civil and Environmental Engineering

University of Washington

U.S. - Japan Workshop on Global Change Climate and Water

January 14, 2003Irvine, CA

Outline of this talk

1) What are the key modes of variability in the (land surface branch of the) water cycle?

2) How is the land surface water cycle changing?

3) What are the implications of possible future changes in the water cycle for human use and water management?

What are the key modes of variability in the land surface

branch of the water cycle?

Seasonal distribution of precipitation across the U.S. (from Linsley et al, 1975)

Mean Diurnal Cycle of precipitation from observations and NCAR/DOE PCM Summer Winter

Observed

PCM

days

Log(

1-P

)Lo

g(1-

P)

days

Roosevelt Dam, AZ

Snoqualmie Falls, WA

Log survivor functions for winter daily precipitation (from Foufoula-Georgiou, 1985)

Variation of standard deviation of storm precipitation with aggregation scale for Darwin storm of 12/24/98 and Kwajelin storm of 12/4/98

Figure courtesy of Efi Foufoula-Georgiou

Cross-correlation of January precipitation for selected west coast sites (from Leytham, 1982)

Clearwater River flood frequency distribution (from Linsley et al 1975)

Pecos River flood frequency distribution (from Kochel et al, 1988)

Serpentine Dam Monthly Rainfall

0

50

100

150

200

250

300

J an Feb Mar Apr May J un J ul Aug S ep Oct Nov Dec

Month

Rai

nfal

l (m

m)

(1911 - 1994)

(1950 - 1994)

(1975 - 1994)

S e rp e n t in e M o n th ly In f lo w

0

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

1 0 0 0 0

1 2 0 0 0

1 4 0 0 0

1 6 0 0 0

1 8 0 0 0

J a n F e b M a r A p r M a y J u n J u l A u g S e p O c t N o v D e c

M o n th

Inflo

w (M

illion

s of

Litr

es) (1 9 1 1 - 1 9 9 4 )

(1 9 5 0 - 1 9 9 4 )

(1 9 7 5 - 1 9 9 4 )

Perth metropolitan water supply total system inflow, 1910-2001

Rio Bravo BasinRio Bravo Basin

Rio Bravo/Rio Conchos total naturalized reservoir inflow, 1954-2001

4978Mm3

(1955 to 1992 avg)

2542 Mm3

(1993 to 2001 avg)

Note: does not include some upstream inflows due to lack of

extended data

Total System Inflow by Water Year

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Inflo

w (M

m3)

Annual number of extreme precipitation events in Tijuana over ~50 years (slide courtesy of Tereza Cavazos)

150000

200000

250000

300000

350000

400000

450000

190

0

191

0

192

0

193

0

194

0

195

0

196

0

197

0

198

0

199

0

200

0

Ap

r-S

ept F

low

(cfs

)

Effects of the PDO and ENSO on Columbia River Summer Streamflows

Cool CoolWarm Warm

150000

200000

250000

300000

350000

400000

450000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Probability of Exceedence

Flo

w (

cfs)

WarmPDO/WarmENSO

WarmPDO/ENSONeut

WarmPDO/CoolENSO

CoolPDO/WarmENSO

CoolPDO/ENSONeut

CoolPDO/CoolENSO

Naturalized Summer Streamflow at The Dalles

0

100000

200000

300000

400000

500000

600000

18

50

18

60

18

70

18

80

18

90

19

00

19

10

19

20

19

30

19

40

19

50

19

60

19

70

19

80

19

90

20

00

Annual Flow at The Dalles 1858-1998

How is the land surface water cycle changing?

Global precipitation trends 1900-99 by season (from IPCC, 2001)

Flow Quantile

Num

ber

of G

ages

Number of U.S. gages, of 395, reporting significantly significant trends (alpha = 0.05) during 1944-93 (from Lins and Slack, 1999)

0.4

0.6

0.8

1

1.2

1.4

1.6

NormalizedStreamflow

Normalized Precip

Linear (NormalizedPrecip)

Linear (NormalizedStreamflow)

Trends in Streamflow and Precipitation, Columbia River basin

0

50000

100000

150000

200000

250000

300000

350000

1858

1870

1882

1894

1906

1918

1930

1942

1954

1966

1978

1990

An

nu

al

Me

an

Flo

w (

cfs)

Annual

5 yr mean

10 yr mean

Annual Flow at The Dalles 1858-1998

U.S. trends in pan evaporation (from Lawrimore and Peterson, 2000)

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 snowpack

Trends in timing of spring snowmelt (1948-2000)

Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan

+20d later–20d earlier

Trends in snowpack

North Vancouver Intensity-duration regression analysis

5-min Duration y = 1.0235x - 1983.7R2 = 0.3501

0

20

40

60

80

100

120

1960 1970 1980 1990 2000

Year

Rai

nfa

ll In

tensi

ty (

mm

/hr)

15-min Duration y = 0.608x - 1177.8R2 = 0.3212

0

10

20

30

40

50

60

1960 1970 1980 1990 2000Year

Rain

fall

Inte

nsi

ty (

mm

/hr)

30-min Duration y = 0.3028x - 581.93R2 = 0.2912

0

10

20

30

40

1960 1970 1980 1990 2000Year

Rai

nfa

ll In

tensi

ty (

mm

/hr)

1-hr Duration y = 0.1341x - 253.67R2 = 0.2662

0

5

10

15

20

25

1960 1970 1980 1990 2000Year

Rai

nfa

ll In

tensi

ty (

mm

/hr)

= statistical outliers

(from Catherine Denault and Rob Millar, UBC)

What are the implications for society?

PCM Business-as-Usual scenarios

Columbia River Basin(Basin Averages)

control (2000-2048)

historical (1950-99)

BAU 3-run average

CORRA

0

20000

40000

60000

80000

100000

120000

oct

dec

feb

apr

jun

aug

Ave

rag

e F

low

(cf

s)

Base

HC

MPI

Typical projected effect of climate change on upper Columbia River discharge, mid-21st Century

2040-2069

60

80

100

120

140

FirmHydropower

Annual FlowDeficit atMcNary

Pe

rce

nt

of

Co

ntr

ol

Ru

n C

lim

ate

PCM Control Climate andCurrent Operations

PCM Projected Climateand Current Operations

PCM Projected Climatewith Adaptive Management

PCM Business-as-Usual Scenarios

Snowpack ChangesCaliforniaApril 1 SWE

Central Valley Water Year Type Occurrence

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Critically Dry Dry Below Normal Above Normal Wet

Water Year Type

Per

cen

t G

iven

WY

Typ

e

hist (1906-2000) 2020s 2050s 2090s

Annual Average Hydrographs, Colorado River

Simulated Historic (1950-1999)Period 1 (2010-2039)Control (static 1995 climate)Period 2 (2040-2069) Period 3 (2070-2098)

Total Basin Storage

Annual Releases to the Lower Basin

target release

Annual Releases to Mexico

target release

Conclusions• Water cycle variability takes many forms, we are only

beginning to understand the interaction of climate and land surface hydrologic variability

• Jury is still out as to whether (and/or which) observed changes in land surface variables are a manifestation of “acceleration of the hyrologic cycle”, or are simply manifestations of natural variability

• If climate change projections are accurate (even as to general direction) hydrologists will be faced with important challenges understanding the interaction of climate and hydrology at the intersection of variability and change (stated otherwise, the time-honored paradigm for hydrologic risk analysis and design must be re-evaluated).