Change in IDF curves for a River basin in southern Ontario

Abstract

This study has concentrated on determining rainfall frequency relationships and percent change analyses over a wide range of storm periods (5 minutes to 48 hours) to understand the temporal and spatial changes in rainfall patterns in Credit River watershed, Ontario, Canada. Two stations (Pearson station and Fergus Shand Dam station) near the watershed were examined by using the radar and rain gauge data. The results showed that the values of Intensity-Duration-Frequency (IDF) curves for various recurrence intervals for the period of 1960-2003 for the Fergus station were found to be much higher than the IDF values of the Pearson station. The percentage difference in rainfall intensities between these two stations for various intervals varied from 2.8% to -43.8%. Also, evaluation of spatial analysis for Pearson and Fergus stations for two different periods (1960 to 1985 and 1986 to 2003) showed that the overall shapes of these curves for these datasets are very different for various durations. Similar comparisons for 1986-2003 period between these two stations showed mixed results for rainfall intensities for various durations and the %change between these stations for various durations ranged from 11.3 to -67.4%. The analyses of temporal changes in rainfall intensities for these stations showed that the rainfall intensities were much lower for all durations for 1986-2003 period when compared with the intensities from 1960-1985 period. Overall, it was concluded that rainfall intensities slightly decreased in recent years for Pearson station. In contrast, for Fergus station, larger duration intensities have been decreased in recent years.