iahs 2013, gothenburg a comparative assessment of awbm and simhyd for forested watersheds bofu yu 1,...

IAHS 2013, Gothenburg

A comparative assessment of AWBM and SimHyd for forested watersheds

Bofu Yu1, Zhongli Zhu2

1School of Engineering, Griffith University, Australia2 School of Geography, Beijing Normal University, China


Background• Workshop objective: to apply and evaluate model

performance in simulating ‘non-stationary’ hydrologic time series;

• Climate and streamflow data were provided for 14 watersheds/catchments around the world;

• Protocol was stipulated for consistency for all modellers;

• AWBM and SimHyd are by far the most commonly used models for streamflow estimation in Australia;

• Two smallest of the 14 watersheds/catchments were selected for comparison purposes.


Two models

AWBM SimHyd

Model type Conceptual Conceptual

Developer Walter Boughton Francis Chiew

Where model developed Brisbane, Australia Melbourne, Australia

Latitude (degree) -27.50 -37.78

Time step Daily Daily

No. of parameters 8 9

Input data requirements Rainfall and potential evaporation

Rainfall and potential evaporation


AWBM


SimHyd


Model comparison

0 20 40 60 80 1000

20

40

60

80

100

Run

off (

mm

)

Excess rain (mm)

AWBM SimHyd SCS-CN

With default parameter values for AWBM and SimHyd, and max. retention value of 105mmfor the SCS Curve Number method,all models show a non-linear relationship between rain excess and runoff.

NB: All the ‘stores’ in AWBM and SimHyd were assumed to be half full initially.


Two watershedsRimbaud Fernow

Country France The U.S.

Watershed The Ruisseau du Rimbaud at Collobrieres

The Fernow EF River at Watershed 6

Closest major city Nice Pittsburgh

Latitude (degree) 44.24 39.07

Area (km2) 1.4 0.2

Period 1967-2006 1959-2009

Land use Forest Forest

Cause for non-stationarity

Fire in 1990 Clearing 1964-68, re-forestation in 1973

Gross runoff coefficient 60% 41%

Solid prec./total prec. <1% 14%


- models developed - watersheds applied


Working Hypotheses

• None of the 2 models is going to work;• Conceptual models would perform better for

watersheds with a higher runoff coefficient and (for these 2) with less snow fall


Two watershedsRimbaud Fernow

Country France The U.S.

Watershed The Ruisseau du Rimbaud at Collobrieres

The Fernow EF River at Watershed 6

Closest major city Nice Pittsburgh

Latitude (degree) 44.24 39.07

Area (km2) 1.4 0.2

Period 1967-2006 1959-2009

Land use Forest Forest

Cause for non-stationarity

Fire in 1990 Clearing 1964-68, re-forestation in 1973

Gross runoff coefficient 60% 41%

Solid prec./total prec. <1% 14%


Model comparisonin terms of the N-S coefficient of efficiency for 30

calibration-validation combinations

AWBM SimHydFernow, the US 0.43±0.11 0.40±0.12Rimbaud, France 0.79±0.07 0.77±0.09

There is a much larger difference between watersheds than between models!!


Model performance in terms of NSE between 2 watersheds

0.0 0.2 0.4 0.6 0.8 1.00

1

2

3

4

5

6

7

8

9

10

No.

Ec

AWBM for Fernow

0.0 0.2 0.4 0.6 0.8 1.00

1

2

3

4

5

6

7

8

9

10

No.

Ec

AWBM for Rimbaud

Histograms of the Nash-Sutcliffecoefficient of efficiency for 30 calibration-validation combinations(level 1 & 2 requirements)


Rimbaud

1965 1970 1975 1980 1985 1990 1995 2000 2005 20100

200

400

600

800

1000

1200

1400

1600

1800

2000F

low

(mm

)

Year

Qobs Qsim

Fire


Rimbaud

1965 1970 1975 1980 1985 1990 1995 2000 2005 20100

20

40

60

80

100S

tand

ardi

sed

cum

ulat

ive

prec

and

flow

Year

cumP cumQ constant


Fernow

1960 1970 1980 1990 2000 20100

200

400

600

800

1000

1200F

low

(m

m)

Year

Qobs Qsim

clearing and reforestation


Fernow

1960 1970 1980 1990 2000 20100

10

20

30

40

50

60

70

80

90

100S

tand

ardi

sed

cum

ulat

ive

prec

and

flow

(%

)

Year

cumP cumQ constant


Observed hydrologic changes at Fernow

Variable Period No. of years Rate(mm.yr-1)

p-value

Precipitation 1959-1986 28 +6.7±3.1 0.04

Streamflow 1959-1986 28 +11.4±2.5 <0.01

Precipitation 1986-2009 24 -2.2±5.5 0.69

Streamflow 1986-2009 24 -10.1±4.6 0.04

Precipitation 1959-2009 51 1.3±1.5 0.40


Fernow

1960 1970 1980 1990 2000 20100

200

400

600

800

1000

1200F

low

(m

m)

Year

Qobs Qsim

clearing and reforestation


Observed hydrologic changes at Rimbaud

Variable Period No. of years Rate (mm.yr-1)

p-value

Precipitation 1968-2006 39 -11.3±4.3 0.01

Streamflow 1968-2006 39 -14.8±4.2 <0.01

Both precipitation and streamflow havesignificantly decreased over the 39 year period.


Rimbaud

1965 1970 1975 1980 1985 1990 1995 2000 2005 20100

200

400

600

800

1000

1200

1400

1600

1800

2000F

low

(mm

)

Year

Qobs Qsim

Fire


Conclusions (what we have learnt from this exercise)

• Difference in model performance is small if calibration method is used consistently;

• Source of non-stationarity is important;• Conceptual models tested are adequate in describing

the effect of changes in precipitation, not the effect of changes in vegetation;

• Changes to streamflow are greater than those in precipitation for these watersheds.


Conclusions ..(what we have learnt from this exercise)

• The effect of the fire in the Rimbaud watershed is secondary in the context of the overwhelming decreasing trend in precipitation and streamflow over the 39 years;

• The 2 conceptual models tested did not perform well for the Fernow (W6) watershed because of the significant increase in streamflow early in the study period, and the subsequent significant decrease in streamflow from 1986. And it snows a lot over there.


Thank You!

iahs 2013, gothenburg a comparative assessment of awbm and simhyd for forested watersheds bofu yu 1,...

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