Analysis of Streamflow Characteristics over Northeastern Canada in a Changing Climate O. Huziy, L. Sushama, M.N. Khaliq, R. Laprise, B. Lehner, R. Roy 1

Outline Motivation Model and experiment description Analysis methodology Validation Climate change results – Ensemble mean approach – Merged (long sample) 2

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 3

Experiment setup Driving data: - CGCM3: 5 current members ( ) and 5 corresponding future members ( ) - ERA40: reanalysis CGCMv3, ERA40 CRCM4 Routing Scheme WATROUTE- modified Runoff* * CRCM4 simulation results were provided by Ouranos team 4 CRCM4 – simulation domain CRCM4 – configuration: 1) resolution – 45 km 2) land surface scheme – CLASS2.7 with 3 soil layers

Experiment setup Driving data: - CGCM3: 5 current members ( ) and 5 corresponding future members ( ) - ERA40: reanalysis CGCMv3, ERA40 CRCM4 Routing Scheme WATROUTE- modified Runoff* * CRCM4 simulation results were provided by Ouranos team 5

Methodology for calculating return levels and assessing uncertainties GEV distribution is used to calculate return levels of extreme events (PDF): 6 Parameters of the distribution obtained by maximizing the probability of the extreme values simulated by the model (GML-method):

Validation with observations Temperature compared to CRU datasetSWE compared to the dataset from Brown et al (2003)

Validation of streamflow 8 Spring high flow Winter low flow Observed Modelled Streamflow (m 3 /s) Modelled Observed The observed data is provided by CEHQ.

CC: Mean values Grid points with non-significant changes at 95% confidence level are shown in grey 9

CC: Timing of the high flow events ( )( ) Change Northern basins Southern basins Generally high flow events tend to occur earlier in future period 10

Modelled timings of high flow events (mean over the ensemble) March-July 11

CC: Return levels of extreme events (separate ensemble members) Changes to return levels of 1-day high flow Changes to return levels of 15-day low flow 12

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 flowLow flow 13

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. 14

Thank you! 15