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Browsing Centre for Hydrology Reports by Author "Pomeroy, John W."
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Item Climate Change in Canadian Floodplain Mapping Assessments(Centre for Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan, 2020) Rajulapati, Chandra Rupa; Tesemma, Zelalem; Shook, Kevin; Papalexiou, Simon Michael; Pomeroy, John W.In the recent decades, precipitation patterns and corresponding streamflow responses in many cold regions catchments have changed considerably due to warming. Understanding historical changes and predicting future responses are of great importance for planning and management of water resources systems. Regional climate simulations using convention- permitting models are helpful in representing the fine-scale cloud and mesoscale processes, which are critical for understanding the physical mechanisms that cause in convective precipitation. From a hydrological perspective, these fine resolution simulations are helpful in understanding the runoff generation mechanisms, particularly for mountainous watersheds, which have high spatial variation in precipitation due to large differences in elevation over small distances. The sister-study of this report, the Bow River Basin Study (BRBS), used a physically based hydrological land surface scheme along with a water management model, coupled with a high resolution convention- permitting atmospheric regional model (Weather Research and Forecasting, WRF) to understand the streamflow generating mechanisms and identify the changes in streamflow responses of the Bow and Elbow River Basins. The coupled model appears to provide a large improvement in predictability, with minimal calibration of parameters and without bias correction of forcing from the atmospheric model. The model4 was able to provide reliable estimates of streamflows, despite the complex topography in the catchment. Using the WRF Pseudo Global Warming (PGW) scenario, estimated future streamflows simulated were then used to develop projected flow exceedance curves. The uncertainty in the simulations is extremely helpful in the risk assessment for downstream flood inundations. However, the uncertainty in streamflows cannot be assessed as the WRF- PGW dataset was only available for a single realization, because of the high computational cost. The research presented in this report focusses instead on using the highly efficient hydrological model developed and verified in BRBS whilst assessing uncertainty using another regional climate model, the CanRCM4, where many realizations are available for different boundary conditions. Since the CanRCM4 simulations have a relatively low resolution, a novel methodology was developed to adjust regional climate model outputs using the WRF-PGW data. An ensemble of 15 CanRCM4 simulations was used to force the Bow River basin model to determine a measure of the uncertainty in the simulated streamflows, and the projected streamflow exceedance probability curves. These curves are extremely useful for risk assessment for downstream flood inundations. Given the importance of understanding how much extreme precipitation will change in urban areas of the basin, where short duration high intensity events cause flash flooding, frequency analysis of these events was carried out for Calgary and Intensity Duration Frequency (IDF) curves were developed. A ready-to-use empirical form of IDF curve has been proposed from this analysis for the City of Calgary. The results from the WRF-PGW modelling indicated that future high flow, low frequency (exceedances less than 10%) streamflow events will decrease compared to those under the current climate condition by 4, 9 and 1.6 m3/s for the Bow River at Banff and Calgary and Elbow River at Sarcee Bridge respectively. The average of the 15 new CanRCM4-WRF-PGW results supports the above result with some greater decreases in streamflow of 9, 16 and 4 m3/s for Bow River at Banff and Calgary and Elbow River at Sarcee Bridge respectively. However, there were some CanRCM4-WRF-PGW realisations that suggested substantial increases in future low frequency streamflow from those indicated by the average CanRCM4- WRF-PGW-drive MESH model. The below average, high frequency (exceedances greater than 30%) future streamflows will increase modestly in all gauging locations by from 1 to 12.5 m3/s. The results of the extreme precipitation analysis at Calgary indicated an increase in future extreme precipitation events of all duration and return periods. On an average an increase of 1.5 times is noted for short return periods (=2, 5), and an increase of 4 times for long return periods (=500, 1000).Item Development of a Snowmelt Runoff Model for the Lower Smoky River(Centre for Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan, 2013) Pomeroy, John W.; Shook, Kevin; Fang, Xing; Brown, Tom; Marsh, ChristopherThe Smoky River tributary of the Peace River has an ungauged (in real-time) basin area of 23,769 km2, corresponding to 46% of its basin area of 51,839 km2 . The purpose of this study was to develop a model to simulate the daily spring ungauged flows of the Smoky River and its main tributary, the Little Smoky River for recent periods using measured meteorological data and forecast periods using the outputs of a numerical weather forecast model. A physically-based model of the ungauged local flows contributing to the Smoky River at Watino and the Little Smoky River at Guy, the Lower Smoky River Model (LSRM), was developed using the CRHM platform. The model was deployed to 26 ungauged sub-basins, from which discharges were routed and accumulated to produce the ungauged discharges at Guy and Watino. The LSRM modelled discharge was evaluated to estimate the discharge of the Smoky River and Little Smoky River in an operational setting with measured meteorological observations. Results from this comparison were very good with a high degree of hydrograph predictability, small bias in flow estimation, and very good prediction of peak daily discharge and excellent prediction of the timing of peak daily discharge. The results were somewhat better for the Smoky River than for the Little Smoky River, showing the effect of increasing basin size in compensating for inadequate precipitation observation density and/or errors in model structure or parameterization. The model has not yet been tested in an operational setting during a spring snowmelt event and its full capabilities and usefulness cannot be assessed until it has been tested in such a setting.Item Informing the Vermilion River Watershed Plan through Application of the Cold Regions Hydrological Model Platform(Centre for Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan, 2012) Pomeroy, John W.; Fang, Xing; Shook, Kevin; Westbrook, Cherie; Brown, TomThe Vermilion River Basin has been identified as one of most altered basins in the North Saskatchewan River Basin by the North Saskatchewan Watershed Alliance. Of all the basin altering activities, wetland drainage is thought to be the most important one in impacting watershed hydrology. The Cold Regions Hydrological Model (CRHM) has had recent developments that make it particularly appropriate to evaluate the impacts of Canadian Prairie wetlands on hydrology. In light of the importance of wetlands in the Vermilion River Basin and the capability of CRHM, this study had five objectives: 1) Setup CRHM for the Vermilion River Basin and conduct preliminary tests using local meteorological data. 2) Develop an improved wetland module that incorporates the dynamics of drained wetland complexes in the physically based, modular Prairie Hydrological Model of CRHM. 3) Refine CRHM results using advances in the improved wetland module, additional parameter data and other adjustments as necessary. 4) Demonstrate scenarios/sensitivity of landscape components such as wetlands and uplands to support planning decisions and make recommendations for land and watershed management. 5) Apply CRHM results to fortify recommendations and support decision making during initial plan implementation. The objectives were addressed with the following methodology. Existing data on precipitation, hydrometeorology, wetland characteristics, stage and extent, drainage pattern and land cover in the Vermilion River Basin were compiled. The existing CRHM Prairie Hydrological Model formulation was set up on the basin and test runs conducted and compared to streamflow hydrographs over multiple years. Then, improvements to the Prairie Hydrological Model formulation of CRHM were made so that CRHM could simulate sequences of many wetlands of varying sizes. The improved model was evaluated through hydrological simulation and quantitative analysis of streamflow and then used in sensitivity analysis of the effect of changing wetland drainage/restoration on streamflow for the Vermilion River. The model was then used to evaluate wetland manipulation and climate scenarios to fortify recommendations, explore options and support decision making for the implementation of the Vermilion watershed plan. The streamflow response of the Vermilion River Basin at its mouth was found to be dominated by channel hydraulics and the control structures in the lower basin and so it is influenced by wetlands only to the extent that the management regime of these control structures is affected by upstream hydrological behaviour of the tributaries with respect to volume and timing of streamflow inputs to the structures. Changes in the upper basin streamflows are more likely to be controlled by changes in the basin hydrological processes rather than in-stream water management and/or channel modifications and therefore the upper basin streamflows are more likely to show the effects of the manipulation of wetland storage.