With approximately 350 km2 drainage area, the Hillsborough River watershed is the largest on Prince Edward Island, equal to one-fifteenth of the total island land mass. There have been numerous flooding events in PE in the past decade resulting from both storm surge and heavy rain. A major storm surge and flooding event occurred on January 21, 2000 which caused the maximum water level in Charlottetown to be exceeded by almost 40 centimetres. As the storm passed through, massive chunks of ice piled up against the shore and the sea rushed in, flooding street and buildings. Hurricane Juan of September 2003 also caused significant flooding and damages. This case study report provides an overview of the development of projected intensity-duration-frequency curves (IDF curves) for the Basin. The objective of the work is to develop IDF curves that reflect the changes in the characteristics of precipitation that might be caused by projected changes in climate. Three time frames were adopted for projections: 2025, 2055 and 2085. This report documents the methodology and findings from each of the tasks. To obtain projected IDF curves, the precipitation intensities in the historical IDF curves were adjusted to reflect projected changes in climate using a statistical modeling technique that is described in detail in the report. Three data sets were used in this work: the local extreme precipitation event data; local monthly climate data; and future projected data from the Global Climate Models.
The results of the assessment show that the Basin is subject to a series of impacts, such as, flash floods resulting from overland flow due to intense precipitation events; and permanent high water levels due to relative sea level rise. Up to 75% of the main stem of the Hillsborough River is subject to tidal influences, and susceptible to flooding resulting from the combined effect of high tides and storm surges. The projected sea level rise and land subsidence in the future may cause an increase in flooding water levels in the flood prone areas.