RECENT HYDROLOGIC CHANGE IN A

COLORADO ALPINE BASIN

An Indicator of Permafrost Thaw ?

Nel Caine

Institute of Arctic & Alpine Research

University of Colorado

Boulder, Colorado

Acknowledgements:

National Science Foundation: Long-Term Ecological Research Program

Mountain Research Station, University of Colorado

Field Technicians: Mark Losleben and Kurt Chowanski

And more Graduate Students than I can name any more!

Introduction

Concern: water resources from mountain environments which are important to populations at lower elevation.

A scale-shift to a single small alpine drainage basin in which we have >30 yr record of discharge and climate.

Upper Green Lakes Valley: part of the City of Boulder’s water supply.

80% of basin as bedrock (granodiorites and gneiss), block slopes and talus.

2.2 km2 catchment above 3550 m elevation above treeline.

Annual precipitation ca. 1000 mm (> 80% as snow).

Specific discharge ca. 1500 mm/yr from the headwaters cirque (Arikaree Glacier), 940 mm at Green Lake 4.

Winter precipitation increased by 2.1 mm/yr (1965-2009) while specific annual discharge increased by 5.4 mm/yr (1982-2010).

Arikaree Glacier

Green Lake 5

Green Lake 4

0

50

100

150

200

250

300

23-Apr 23-May 22-Jun 22-Jul 21-Aug 20-Sep 20-Oct

Da

ily D

isc

ha

rg

e (

l/s

)

Albion

0

200

400

600

800

1/1

3/1

5/1

7/1

9/1

11/1

Me

dia

n D

isch

arg

e (

l/s

)

Trend = -0.49 d/yr

R2 = 0.215

5/3

5/13

5/23

6/2

6/12

6/22

7/2

7/12

7/22

8/1

1960 1970 1980 1990 2000 2010

Da

te o

f P

ea

kPeak

Trend = -1.18 d/yr

R2 = 0.461

Start

Trend = -0.75 d/yr

R2 = 0.431

4/23

5/3

5/13

5/23

6/2

6/12

6/22

7/2

7/12

7/22

1980 1985 1990 1995 2000 2005 2010

Start

Peak

Middle Boulder Creek (94 km2 area, above2500 m)

Upper Green Lakes (2.2 km2, above 3550 m)

Stewart et al. 2006

However, a further change, not evident elsewhere, occurs in the late-season

hydrograph: a flatter recession and an increase in flows at Green Lake 4 (also at

Albion, down-valley).

Sep-Oct

Trend = 2.66 mm/yr

R2 = 0.3644

0

50

100

150

200

250

300

1980 1985 1990 1995 2000 2005 2010

Dis

ch

arg

e (

mm

)

September-October Flows (mm) at Green Lake 4

Trend at Middle Boulder Creek (2500m, 940000ha): 0.03 mm/yr (NS)

at Albion (3250m, 709.7ha): 2.43 mm/yr (p<0.001)

at Navajo (3730m, 41.8ha): -1.9 mm/yr (NS)

Changes in seasonal hydrograph consistent with those elsewhere: Forward shift in start

Forward shift in peak flow

No change in peak flow volume

Almost 50% of annual increase

An Explanation of Increased Autumn Flow in Green Lakes

Valley ?

Trend = -0.265 mm/yr

R2 = 0.002

0

50

100

150

200

250

300

1980 1985 1990 1995 2000 2005 2010

Sept-Oct Precipitation

An Explanation of Increased Autumn Flow in Green Lakes

Valley ?

Trend = -0.265 mm/yr

R2 = 0.002

0

50

100

150

200

250

300

1980 1985 1990 1995 2000 2005 2010

Trend = 0.54 cm/yr

R2 = 0.03910

20

40

60

80

100

1980 1984 1988 1992 1996 2000 2004 2008

Ab

l(cm

/y)r

)

Sept-Oct Precipitation Sept Ablation Arikaree Glacier

An Explanation of Increased Autumn Flow in Green Lakes

Valley ?

Trend = -0.265 mm/yr

R2 = 0.002

0

50

100

150

200

250

300

1980 1985 1990 1995 2000 2005 2010

Equivalent Trends in Flow at Green Lake 4

Discharge Trend -2.66 mm/yr

Precipitation Trend -0.25

Glacier Melt (*2) 0.46

? 2.45

Trend = 0.54 cm/yr

R2 = 0.03910

20

40

60

80

100

1980 1984 1988 1992 1996 2000 2004 2008

Ab

l(cm

/y)r

)

Sept-Oct Precipitation Sept Ablation Arikaree Glacier

An Explanation of Increased Autumn Flows in Green

Lakes Valley ?

This leaves the possibility of a subsurface source(s):

(1) The melting of ice-rich permafrost

(2) An increased ground water contribution

And, the two should be linked as (1) would lead to (2)

Permafrost in Upper Green Lakes Valley (J.Janke)

Trend = 15.7 DD/yr

R2 = 0.437

0

200

400

600

800

1000

1200

1400

1980 1985 1990 1995 2000 2005 2010

D.D

.

Accumulated Degree-Days at D-1 (Niwot Ridge)

A Geochemical Signal from the Rock Glacier at Green Lake 5

0

1000

2000

3000

4000

5000

6000

7000

0 1000 2000 3000 4000 5000 6000

Ca (uEq/l)

SO

4 (u

Eq

/l)

Ca & SO4 from weathering of pyrite, epidote and

chlorite in metamorphic bedrock and debris

(Williams et al. P.P.P. 2006)

A Geochemical Signal from the Rock Glacier at Green Lake 5

0

20

40

60

80

100

120

140

160

180

200

1980 1985 1990 1995 2000 2005 2010

Ca

(u

Eq

/L)

GL4

GL5

NAV

ARK

0

20

40

60

80

100

120

140

160

180

1980 1985 1990 1995 2000 2005 2010

SO

4 u

Eq

/LGL4

GL5

NAV

ARK

Ca & SO4 in stream water: Green Lakes, Sept-Oct

0

1000

2000

3000

4000

5000

6000

7000

0 1000 2000 3000 4000 5000 6000

Ca (uEq/l)

SO

4 (u

Eq

/l)

Ca & SO4 from weathering of pyrite, epidote and

chlorite in metamorphics (Williams et al. P.P.P.

2006)

With a similar signal in stream water at GL4 and GL5,

starting in 2000 but not evident at higher elevations (NAV

and ARK).

Conclusion

The flows from Green Lakes Valley flows show a forward shift in the seasonal

hydrograph similar to that at lower elevations in the western US.

They also show an increase in late-season (September – October) flows not

seen at lower elevations.

The late-season increase seems to be best explained by the thawing of alpine

permafrost, most likely on the north-facing slopes of the valley.

That part of it which derives from storage as glacier ice (slight) or ground ice

should run down as storage is depleted but, at present, accounts for half

of the observed increase in annual flows.

It does not represent a significant addition to the water resources of North

Boulder Creek (which supplies about 40% of the City of Boulder’s

supply).