Recent hydrologic change in a Colorado alpine basin: an indicator of permafrost thaw? [Nel Caine]

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Recent hydrologic change in a Colorado alpine basin: an indicator of permafrost thaw? Presented by Nel Caine at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.

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Recent hydrologic change in a Colorado alpine basin: an indicator of permafrost thaw? [Nel Caine]

  1. 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, ColoradoAcknowledgements: 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. 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).
  3. 3. 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
  4. 4. 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 2010Stewart et al. 2006
  5. 5. 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)
  6. 6. An Explanation of Increased Autumn Flow in Green Lakes Valley ? Sept-Oct Precipitation300 Trend = -0.265 mm/yr250 R2 = 0.00220015010050 0 1980 1985 1990 1995 2000 2005 2010
  7. 7. An Explanation of Increased Autumn Flow in Green Lakes Valley ? Sept-Oct Precipitation Sept Ablation Arikaree Glacier300 100 Trend = -0.265 mm/yr250 R2 = 0.002 80 Abl(cm/y)r)200 60150 40100 20 Trend = 0.54 cm/yr50 R2 = 0.0391 0 0 1980 1985 1990 1995 2000 2005 2010 1980 1984 1988 1992 1996 2000 2004 2008
  8. 8. An Explanation of Increased Autumn Flow in Green Lakes Valley ? Sept-Oct Precipitation Sept Ablation Arikaree Glacier300 100 Trend = -0.265 mm/yr250 R2 = 0.002 80 Abl(cm/y)r)200 60150 40100 20 Trend = 0.54 cm/yr50 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
  9. 9. 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
  10. 10. 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)
  11. 11. 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 120Ca (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
  12. 12. ConclusionThe 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).

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