Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Engineering Science


Civil and Environmental Engineering


Najafi, M. Reza


It is widely recognized that climate change can impact the risks of flooding in many regions around the world especially the low-lying coastal areas. The concurrent occurrence of multiple flood drivers such as high river flows and coastal water levels can aggravate such impacts causing catastrophic damages. In this study, the individual and compounding effects of riverine and coastal flooding are investigated over Stephenville Crossing, a town located in the coastal-estuarine region of Newfoundland and Labrador (NL), Canada. The impacts of climate change on flood characteristics and the corresponding uncertainties associated with model inputs and structure, and emission scenarios are assessed. A hydrologic model (HEC-HMS) and a 2D hydrodynamic model (HEC-RAS 2D) are setup and calibrated to simulate the flood inundation for the historical period (1976-2005) as well as near future (2041-2070) and far future (2071-2100) periods under Representative Concentration Pathways (RCPs) 4.5 and 8.5. Results of the HEC-RAS 2D model, including the water surface elevations, are then compared with the 1D model simulations. Future storm events are generated based on projected Intensity-Duration-Frequency (IDF) curves from the convection-permitting Weather Research and Forecasting (WRF) climate model simulations, using SCS, Huff, and alternative block design storm methods. The results are compared with simulations based on projected IDF curves that are derived from statistically downscaled General Circulation Models (GCMs) and the uncertainties from different sources are quantified. Overall, the compounding effects of river overflows, sea-level rise, storm surge and wave can result in extensive inundation of the study area under climate change. The uncertainties associated with climate change impact analyses are propagated from GCMs to flood inundation estimations through design storms, projected IDF curves and modeling processes. Simulations based on projected WRF-IDF curves show higher risks of flooding compared to the ones associated with GCM-IDFs. This research provides a new approach to apply projected IDF curve for compound flood analysis under changing climate conditions.

Summary for Lay Audience

Flooding is one of the most common natural disasters in Canada which has negative impacts on the economy, society, and environment. More than 600 flood events are recorded in Newfoundland and Labrador’s (NL) Flood Events Inventory over the period of 1950-2011 (Atlantic Climate Adaption Solutions Association, 2012). Stephenville Crossing is situated on the west coast of Newfoundland, and the town is located between St. George’s River estuary and Rothesay Bay. The location of community makes it vulnerable to both coastal and riverine flooding. The combination of multiple extreme events can cause more catastrophic consequences compared to the individual extreme occurrences. Multiple factors will increase flood risks in Canada with changing climate extremes, including more intense rainfall, warmer temperature, local land subsidence and global sea level rise (Canadian Changing Climate Report, 2019). The interactions between future climate and extreme hazards indicate that it is vital to include climate change analysis in flood analysis. Calibrated hydrological model (HEC-HMS) and two-dimensional hydrodynamic model (HEC-RAS) are used to investigate the individual and combined effects of fluvial and coastal flooding. The flood characteristics based on different projected Intensity-Duration-Frequency (IDF) (generated based on GCMs and high-resolution convection-permitting WRF simulations) are compared. Further, the uncertainties in the generated hyetographs and model parameters are quantified.