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Evaluating Long-term Trends and Variations in Daily and Extreme Precipitation Indices over Western Canada Open Access


Other title
Mann-Whitney-Pettitt test
precipitation trend analysis
Type of item
Degree grantor
University of Alberta
Author or creator
Fu, Xiaoqing
Supervisor and department
Dr. Thian Yew Gan (Civil and Environmental Engineering)
Examining committee member and department
Dr. Peter Steffler (Civil and Environmental Engineering)
Dr. David Chanasyk (Renewable Resources)
Dr. Thian Yew Gan (Civil and Environmental Engineering)
Department of Civil and Environmental Engineering

Date accepted
Graduation date
Master of Science
Degree level
Continuous and long weather records are essential to assess possible long-term, hydrologic/climatic changes at local and regional scales by applying appropriate statistical analysis on daily climate data that may require data quality control, adjustments or gap filling of missing data. In this study, a statistical technique called Markov chain was employed to gap fill missing values of daily precipitation observed at 30 stations in western Canada. The gap filling approach was based on 20 years of selected historical meteorological data. The statistical properties of the daily precipitation data with gap filled values are compared with those of the original data (before gap filling) to ensure that this approach preserves the statistical characteristics of the historical data. Next, after gap filling precipitation data of those selected stations in western Canada with missing values, ten precipitation indices that represent different precipitation properties were computed from daily data of a total of 30 climate stations, each with at least 50 years of record length (up to 2006). Statistical tests such as the Mann-Whitney-Pettitt statistics and linear regression were used to detect possible change points present and trend magnitudes of these precipitation indices. Results reveal that an increasing trend in the maximum number of consecutive wet days and the annual maximum monthly 5-day precipitation and a decreasing trend in the maximum number of consecutive dry days over majority of the stations of Western Canada. Except for a small area located in southern British Columbia, the annual total precipitation index of many stations had increased but only about 1/3 of these stations show a statistically significant increase in the annual total precipitation index. However, no consistent change was detected in the number of days when precipitation is equal and greater than 10 mm or 20 mm. Finally, indices of many stations in the Prairie Provinces for the annual monthly maximum 1-day precipitation, precipitation that exceeds the 95 and 99 percentile thresholds, and simple precipitation intensity index (SDII) have decreased but only some of changes are statistically significant. In contrast, no consistent changes in these extreme precipitation indices were detected in British Columbia.
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File title: Evaluating Long-term trends and variations in daily and extreme precipitation indices over Western Canada
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