Investigation and comparison of different methods of trend analysis of rainfall in Tabriz synoptic station

Document Type : Research Article

Authors

1 Civil Engineering Department, Faculty of Engineering, Azarbaijan Shahid Madani University, Tabriz, Iran

2 Water resources engineering department, Faculty of Civil engineering, Tabriz, Iran.

10.22060/ceej.2026.23138.8115

Abstract

In this study, the temporal trend of monthly rainfall changes for the time period of 1951 to 2022 in Tabriz Synoptic Station was examined and compared using different methods. Nonparametric tests including Mann-Kendall test and sequential Mann-Kendall test and Şen's innovative graphical trend analysis method were used to identify the potential rainfall trend. In addition, wavelet transform and Mann-Kendall statistical tests were used to understand the main structure of the trend in rainfall as well as the time scales affecting the trend. The trend analysis methods were compared with each other to obtain a valid result. The results obtained from different methods indicate the presence of a negative trend in the precipitation changes of the Tabriz station. The results also show that the standard Mann-Kendall nonparametric test is better in this case study for producing statistically significant trends in rainfall compared to the modified Mann-Kendall test. The results of the wavelet-based analysis method and the hybrid wavelet Mann-Kendall analysis method showed that at the monthly scale, intraannual periods (2 to 8 months) with high frequency have the greatest impact on creating trends in the monthly rainfall time series of the Tabriz synoptic station. The sequential Mann-Kendall curves detected the approximate onset of a developing negative trend from 1995 to the end of the study period. The Şen graphical method also indicated a negative trend during the years 1987-2022 compared to 1951-1986, with a steeper decreasing trend for "high" rainfall values.

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Amirkabir Journal of Civil Engineering
Volume 57, Issue 11
February 2026
Pages 1921-1938

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