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A comparative assessment of AWBM and SimHyd for forested watersheds

A comparative assessment of AWBM and SimHyd for forested watersheds. Bofu Yu 1 , Zhongli Zhu 2 1 School of Engineering, Griffith University, Australia 2 School of Geography, Beijing Normal University, China. Background.

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A comparative assessment of AWBM and SimHyd for forested watersheds

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  1. A comparative assessment of AWBM and SimHyd for forested watersheds Bofu Yu1, Zhongli Zhu2 1School of Engineering, Griffith University, Australia 2School of Geography, Beijing Normal University, China

  2. 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.

  3. Two models

  4. AWBM

  5. SimHyd

  6. Model comparison With default parameter values for AWBM and SimHyd, and max. retention value of 105mm for 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.

  7. Two watersheds

  8. - watersheds applied - models developed

  9. 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

  10. Two watersheds

  11. Model comparisonin terms of the N-S coefficient of efficiency for 30 calibration-validation combinations There is a much larger difference between watersheds than between models!!

  12. Model performance in terms of NSE between 2 watersheds Histograms of the Nash-Sutcliffe coefficient of efficiency for 30 calibration-validation combinations (level 1 & 2 requirements)

  13. Rimbaud

  14. Rimbaud

  15. Fernow

  16. Fernow

  17. Observed hydrologic changes at Fernow

  18. Fernow

  19. Observed hydrologic changes at Rimbaud Both precipitation and streamflow have significantly decreased over the 39 year period.

  20. Rimbaud

  21. 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.

  22. 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.

  23. Thank You!

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