Utilizing Wavelet Transforms and the Mann-Kendall Test to Assess Trends in Surface Air Temperature over Southern Ontario and Québec

Abstract

Abstract. This paper explored trends in the mean surface air temperature over the southern parts of Ontario and QuA©bec, Canada, for the period of 1967-2006. The most dominant periodicities affecting trends in different temperature data categories were determined. The data from a total of five stations were used (monthly, seasonal, and annual). The methods used in the data analysis included the discrete wavelet transform (DWT), the Mann-Kendall (MK) trend test, and sequential Mann-Kendall analysis – combining the use of these techniques is new in temperature trend studies, and has not been explored in detail, particularly in Canada. The mother wavelet, number of decomposition levels, and boundary condition were determined using a newly proposed criterion based on the relative error of the MK Z-values between the original data and the approximation component of the last decomposition level. It was determined that all stations experienced positive trends, and significant trends were observed in all of the monthly and annual data. For the different seasons, although the trend values were all positive, not all stations experienced significant trends. For monthly data, high-frequency components ranging from 2 to 12 months were more prominent for trends. The positive trends observed for the annual data are thought to be related to warming during winter and summer seasons, which are manifested in the form of multi-year to decadal events of between 8 and 16 years.