HYDROGRAPH SEPARATION

THE LONG TERM RESPONSE OF STREAM FLOW TO CLIMATIC WARMING IN HEADWATER STREAMS OF

INTERIOR ALASKA

Jay JonesAmanda Rinehart

WATERSHED HYDROLOGY WITH DISCONTINUOUS PERMAFROST

PermafrostDeeper mineral regions

Organic

Mineral

Permafrost

Flow

Early Summer

Late Summer

• WITH PERMAFROST, FLOWS THROUGH WATERSHEDS RESTRCITED TO SOIL AND UPPER MINERAL REGIONS

• TRANSITION FROM SOIL TO MINERAL LAYERS OVER SUMMER WITH INCREASING DEPTH OF THAW

STREAM HYDROLOGY WITH DISCONTINUOUS PERMAFROST

Bolton 2006

STORM FLOW HYDROLOGY

SEASONAL CHANGES IN STORM FLOW RESPONSECONTINUOUS PERMAFROST

McNamara et al. 1997

Tracer: Electrical conductanceOld water: Stream water during base flowNew water: Water tracks

Petrone et al. 2007

CPCRW STORM FLOW END MEMBER SEPARATION

Tracers: DOC and Ca2+

End members: Precipitation, soil water, and ground water

Petrone et al. 2007

CPCRW STORM FLOW END MEMBER SEPARATION

Petrone et al. 2007

CPCRW STORM FLOW END MEMBER SEPARATION

CPCRW SEASONAL CHANGE IN STORM FLOW CONTRIBUTIONS

Bolton 2006

LONG-TERM PATTERNS IN TOTAL DISCHARGE

Year

1975 1980 1985 1990 1995 2000 2005

Q (

L/s/

ha)

0

5

10

15

20

25

30

35C2C3C4

Bolton et al. 2004

OBJECTIVES

1) Determine how stream flow varied among streams draining watersheds with varying extents of permafrost

2) Evaluate if stream hydrology is changing with loss of permafrost.

Can we detect a change in source water contribution with loss of permafrost?

STUDY SITES

DATA SOURCESData :

• C2 & C3: 1978 – 2007

• C4: 1980 to 2007

• Pressure transducers and data loggers

• Flumes - C2, C3, C4

• Stage height data logged every 15 minutes to 1 hour

• June 1 – September 30 (defined as active season)

HYDROGRAPH SEPARATIONLOCAL-MINIMUM METHOD

1995

6/1 7/1 8/1 9/1 10/1

Dis

char

ge (

L s-1

)

0

50

100

150

200

250

Stream flowBase flow

H1: The rate at which precipitation and storm flows are transmitted to streams is governed by the extent of permafrost and thus the extent of a confining layer in watersheds

• Base and storm flow separated with a sliding window to identify local minimums in flow

• Size of window defined by watershed size (I = 10 Area0.1)

• Baseflow calculated by linearly interpolating runoff between consecutive notes of minimum flow

• Prediction: The streams draining the lower permafrost watersheds will have a greater baseflow contribution

STORM FLOW RECESSION ANALYSIS

H2: The rate at which storm flows are released from storage will decline over the active season as the depth of seasonal soil thaw deepens and storage zone volume increases

H3: Over longer time scales, with a loss of permafrost, stream flows will become less responsive to precipitation as storage zone increases, and storm flows will contribute less to overall stream discharge

• Flood recessions analyzed for all storms lasting longer than 12 hours 8/20/1995 8/22/1995 8/24/1995

Dis

char

ge (

L s-1

)

0

10

20

30

40

50

60

70

80

Stream flowRecession curve; Qt = Q0e

-kt

STORM FLOW RECESSION ANALYSIS

Prediction: The storm flow recession curve coefficient (k) will decline over the active season

Prediction: If permafrost thaw is affecting stream discharge, then across years, the seasonal change in storm flow recessions will increase as active layer depth increases and permafrost in valley bottoms degrades.

Q (

L/s)

Day of Active Season

Sto

rm f

low

rec

essi

on (

k; d

-1)

Yea

rs

Year 1

k1k2

Qt = Q0e-kt

PRECIPITATION

1980 1985 1990 1995 2000 2005

Mea

n da

ily p

reci

pita

tion

(mm

)

0.0

0.5

1.0

1.5

2.0

2.5

HYDROGRAPH SEPARATIONC2 (4%)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6Total flowBase flow

C4 (19%)

Mea

n su

mm

er d

isch

arge

(m

m)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

C3 (53%)

1980 1985 1990 1995 2000 20050.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

(mm d-1) (%)

Total 0.58

Base flow 0.46 79

Storm flow 0.12 21

(mm d-1) (%)

Total 0.52

Base flow 0.23 44

Storm flow 0.29 66

(mm d-1) (%)

Total 0.60

Base flow 0.49 82

Storm flow 0.11 18

STORM FLOW RECESSION

C2

0.0

0.2

0.4

0.6

0.8

1.0

C4

Sto

rm fl

ow r

eces

sion

(d-1

)

0.0

0.2

0.4

0.6

0.8

1.0

C3

Day of year

140 160 180 200 220 240 260 280 3000.0

0.2

0.4

0.6

0.8

1.0

STORM FLOW RECESSION – INTERANNUAL CONTROLS

-0.004

0.000

0.004

0.008

Sea

sona

l cha

nge

stor

m r

eces

sion

s (d

-2)

-0.004

0.000

0.004

0.008

Temperature (°C)

11 12 13 14 15

-0.004

0.000

0.004

0.008

C2

C3

Precipitation (mm)

0 1 2 3

C4

STORM FLOW RECESSIONLONG-TERM CHANGES

1980 1985 1990 1995 2000 2005Sea

sona

l cha

nge

in s

torm

rec

essi

ons

(d-2

)

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

0.008

0.010C2C3C4C2 change

CONCLUSIONS

• The loss of permafrost will have fundamental impacts on streams in the boreal forest of interior Alaska • While we did not detect significant inter-annual changes in most measures of stream flow in CPCRW, we did observe distinct differences in summer runoff among streams • The patterns among streams of CPCRW are consistent with inter-annual hydrologic changes observed throughout the subarctic including changes in the seasonal distribution of river flow (Walvoord and Striegl 2007), size of ponds (Riordan et al. 2006), glacial recession (Kaser et al. 2006), and declines in snow cover duration (Brown and Braaten 1998)

• With climate warming and loss of permafrost, upland headwater stream flow will likely become less responsive to precipitation and streams may become ephemeral

• These changes in stream flow are one component of broader hydrologic change across the boreal forest of Alaska.