1) Streamflow data from an alpine basin in Colorado shows an increase in late-season (September-October) flows not observed elsewhere, in addition to the typical earlier peak flow. 2) This increase is best explained by melting of ice-rich permafrost on north-facing slopes, as supported by increasing groundwater contributions and chemical signatures. 3) The melting permafrost currently accounts for about half of the total observed increase in annual streamflow from the basin.

1. 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!

2. 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).

4. Green Lake 4
300
Daily Discharge (l/s)
250
200
150
Arikaree Glacier 100
50
0
23-Apr 23-May 22-Jun 22-Jul 21-Aug 20-Sep 20-Oct
Albion
800
Median Discharge (l/s)
Green Lake 5 600
400
200
0 1/1
3/1
5/1
7/1
9/1
11/1

5. Middle Boulder Creek (94 km2 area, above2500 m)
8/1
7/22 Trend = -0.49 d/yr
7/12 R2 = 0.215
Date of Peak
7/2
6/22
6/12
6/2
5/23
5/13
5/3
1960 1970 1980 1990 2000 2010
Upper Green Lakes (2.2 km2, above 3550 m)
7/22 Start
Peak Peak
7/12 Trend = -1.18 d/yr
7/2 R2 = 0.461
6/22
6/12
6/2
5/23
5/13 Start
Trend = -0.75 d/yr
5/3
R2 = 0.431
4/23
1980 1985 1990 1995 2000 2005 2010
Stewart et al. 2006

6. Changes in seasonal hydrograph consistent with those elsewhere:
Forward shift in start
Forward shift in peak flow
No change in peak flow volume
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).
300
Sep-Oct
250
Discharge (mm)
200
150 Almost 50% of annual increase
100
Trend = 2.66 mm/yr
50
R2 = 0.3644
0
1980 1985 1990 1995 2000 2005 2010
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)

7. An Explanation of Increased Autumn Flow in Green Lakes
Valley ?
Sept-Oct Precipitation
300
Trend = -0.265 mm/yr
250 R2 = 0.002
200
150
100
50
0
1980 1985 1990 1995 2000 2005 2010

8. An Explanation of Increased Autumn Flow in Green Lakes
Valley ?
Sept-Oct Precipitation Sept Ablation Arikaree Glacier
300 100
Trend = -0.265 mm/yr
250 R2 = 0.002 80
Abl(cm/y)r)
200
60
150
40
100
20 Trend = 0.54 cm/yr
50
R2 = 0.0391
0
0
1980 1985 1990 1995 2000 2005 2010 1980 1984 1988 1992 1996 2000 2004 2008

9. An Explanation of Increased Autumn Flow in Green Lakes
Valley ?
Sept-Oct Precipitation Sept Ablation Arikaree Glacier
300 100
Trend = -0.265 mm/yr
250 R2 = 0.002 80
Abl(cm/y)r)
200
60
150
40
100
20 Trend = 0.54 cm/yr
50
R2 = 0.0391
0
0
1980 1985 1990 1995 2000 2005 2010 1980 1984 1988 1992 1996 2000 2004 2008
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

10. 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) Accumulated Degree-Days at D-1 (Niwot Ridge)
1400
1200
1000
800
D.D.
600
400 Trend = 15.7 DD/yr
R2 = 0.437
200
0
1980 1985 1990 1995 2000 2005 2010

11. A Geochemical Signal from the Rock Glacier at Green Lake 5
7000
Ca & SO4 from weathering of pyrite, epidote and
6000
chlorite in metamorphic bedrock and debris
5000
(Williams et al. P.P.P. 2006)
SO (uEq/l)
4000
4
3000
2000
1000
0
0 1000 2000 3000 4000 5000 6000
Ca (uEq/l)

12. A Geochemical Signal from the Rock Glacier at Green Lake 5
7000
Ca & SO4 from weathering of pyrite, epidote and
6000
chlorite in metamorphics (Williams et al. P.P.P.
5000
2006)
SO (uEq/l)
4000
4
3000
2000
1000
0
0 1000 2000 3000 4000 5000 6000
Ca (uEq/l) With a similar signal in stream water at GL4 and GL5,
starting in 2000 but not evident at higher elevations (NAV
and ARK).
Ca & SO4 in stream water: Green Lakes, Sept-Oct
200 180
180 GL4 160 GL4
160 GL5 140 GL5
140 NAV NAV
120
Ca (uEq/L)
SO4 uEq/L
120 ARK 100 ARK
100
80
80
60 60
40 40
20 20
0 0
1980 1985 1990 1995 2000 2005 2010 1980 1985 1990 1995 2000 2005 2010

13. 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).