analysis of streamflow characteristics over northeastern canada in a changing climate o. huziy, l....

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Analysis of Streamflow Characteristics over Northeastern Canada in a Changing Climate

O. Huziy, L. Sushama, M.N. Khaliq, R. Laprise, B. Lehner, R. Roy

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Outline

• Motivation• Model and experiment description• Analysis methodology• Validation• Climate change results– Ensemble mean approach– Merged (long sample)

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Motivation

• Better understanding of processes involved in winter and spring flow regimes

• Compare the approaches of merged samples and of ensemble mean for analysing climate change signal in return levels of extreme events

• Validate river model with observations

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Experiment setup

Driving data:- CGCM3: 5 current members (1970-1999) and 5 corresponding future members (2041-2070)- ERA40: reanalysis

CGCMv3,ERA40

CRCM4

Routing SchemeWATROUTE-modified

Runoff*

* CRCM4 simulation results were provided by Ouranos team

CRCM4 – simulation domain

CRCM4 – configuration:1) resolution – 45 km2) land surface scheme – CLASS2.7 with 3 soil layers

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Experiment setup

Driving data:- CGCM3: 5 current members (1970-1999) and 5 corresponding future members (2041-2070)- ERA40: reanalysis

CGCMv3,ERA40

CRCM4

Routing SchemeWATROUTE-modified

Runoff*

* CRCM4 simulation results were provided by Ouranos team

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Methodology for calculating return levels and assessing uncertainties

• GEV distribution is used to calculate return levels of extreme events (PDF):

• Parameters of the distribution obtained by maximizing the probability of the extreme values simulated by the model (GML-method):

Validation with observationsTemperature compared to CRU dataset SWE compared to the dataset from

Brown et al (2003)

Validation of streamflow

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Spring high flowW

inter low flow

Observed

Mod

elle

d

Stre

amflo

w (m

3 /s)

Modelled

Observed

The observed data is provided by CEHQ.

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CC: Mean values

Grid points with non-significant changes at 95% confidence level are shown in grey

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CC: Timing of the high flow events(1

970-

1999

)

(204

1-20

70)

Change

Northern basins

Southern basins

Generally high flow events tend to occur earlier in future period

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Modelled timings of high flow events (mean over the ensemble) March-July

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CC: Return levels of extreme events (separate ensemble members)

Chan

ges

to re

turn

leve

ls o

f 1-d

ay h

igh

flow

Chan

ges

to re

turn

leve

ls o

f 15-

day

low

flow

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CC: Return levels of extreme events (merged samples)

• There appear some significant changes to the high-flow return levels in the case of the merged sample analysis.

• Since the changes are the same as in the mean sample analysis, this means that the uncertainties related to the estimation of distribution parameters have decreased.

• Changes to the return levels corresponding to smaller return periods (10 years) are more significant than for the longer return periods (30 years)

High flow Low flow

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Conclusions• The models reproduce reasonably mean hydrographs and

values of spring peaks.• The model has difficulties to reproduce winter flow,

probably due to the absence of drainage in the regions with near surface bedrock.

• It is shown that the longer samples can be more reliable when assessing climate change signal in high flow return levels.

• The studies with different GCMs and RCMs are required to increase the confidence in the obtained climate change results.

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Thank you!