|Citation||Rodenhuis, D, Music, B, Braun, M and Caya, D. 2011. Climate diagnostics of future water resources in BC Watersheds: Regional climate modelling diagnostics project final report. Pacific Climate Impacts Consortium.|
|Abstract/Description or Keywords||Climate modelling technology was used to estimate future hydrologic conditions under the influence of
climate variability and change. The objectives for this work were: i) to validate the water balance in
selected watersheds, ii) to simulate future conditions in the 2050s and, iii) to contribute to estimates of
future streamflow. The selected watersheds for this project included the Upper Columbia and Upper
Peace rivers in British Columbia. Results for the smaller Campbell watershed were also reviewed, but
were not considered reliable. Results for other watersheds, the Upper Fraser and the entire Columbia
Basin, were computed as a reference.
The A2 emissions scenario was used to drive several versions of a Canadian Coupled Global Climate
Model (CGCM). Those results were used subsequently to drive several different versions of the Canadian
Regional Climate Model (CRCM) at 45 km horizontal resolution. The CRCM employs an implicit Land
Surface Scheme (LSS) to resolve the hydrologic components: precipitation, surface evapotranspiration,
snow accumulation, and surface runoff.
The results from climate models were compared to historical records (1961-1990) to determine model
bias, the effects of internal (and natural) variability, and to test for structural uncertainty due to different
parameterizations of physical processes. These results are used to estimate the overall uncertainty of
hydro-climatic projections in the future (2050s). The experimental setup allows the estimation of several
sources of uncertainty associated with hydro-climatic projections. A Results Matrix was developed as an
analysis tool for systematically analyzing hydrologic impacts and their variability from climate models.
The monthly mean time series of historical and future conditions were examined for bias, internal
variability, and climate change signal. The annual average results from the integrated response of both the
global and regional climate models in selected major watersheds of British Columbia are:
The CGCM has a significant cold bias that is accompanied by excess snow accumulation during
winter. However, the bias may be removed by considering anomalies between the future and
historical projections taken from the same model.
Most of the internal variability comes from the global climate model, which is the source of our
best estimate of the natural variability in the real climate system. The influence of internal
variability on estimates of the projected change in the climatological values of the hydrologic
components in the major watersheds of British Columbia is estimated to be less than 6% for both
snow accumulation and runoff.
The impact of the climate change signal in the 2050s decreased the annual mean value of the
snow accumulation by about 2% in the Upper Peace, 6% in the Upper Columbia, and a decrease
of almost 20% for the entire Columbia Basin, relative to projected mean annual climatology. The
peak period in surface runoff is shifted to earlier in the spring. The impact in the Upper Peace
(and Fraser watershed) is an increase in runoff by 17-18%, but less in the south for the Upper
Columbia (9%) and the entire Columbia Basin (7%).
Finally, ensembles of time series of monthly averaged runoff and hydrologic components for future
conditions in the designated watersheds were computed from both global and regional climate models
(Attachment 1). These were used for comparison with detailed hydrologic modelling in a synthesis report,
Climate Change Impacts on Hydro-Climatic Regimes in the Peace and Columbia Watersheds, British
Columbia, Canada (Shrestha et al. 2011).
|Sub-watershed if known|