Md. Sabbir Hossen,

Trend analysis may be useful.

Regards

Dear Aristidis Matsoukis

Thank you for your valuable answer.

Do you have any specific recommendation for me on which tool/function should I prefer for Trend Analysis.

This is a very difficult question to answer because it is not sufficiently specific. Your readers can't tell what you're trying to achieve. For example:

• Is this a homework assignment about methods your instructor has mentioned in class?
• Is your instructor asking you to go to the library and look up various methods. If so google "statistical tools in hydrology"
• Are you trying to understand if rainfall intensities or frequencies have changed historically? And if the have changed, have they changed within the range of error of measuring or calculating such changes? What might be the implications of such error distributions?
• Has the rainfall for which a large dam has been designed changed and is it likely to change under different climate change scenarios? And if so, will it increase or decrease the chances of loss of life?
• Have rainfall patterns shifted geographically, thus requiring changes in the types of crops grown? Or movement of large populations?
• Has historical precipitation changed from primarily snow to liquid form. If so, has this change happened "suddenly" when temperatures cross a particular threshold? Or has it perhaps been a smooth or continuous change?
• Don't forget that the possible historical nature of rainfall may not represent future changes.

Hope this helps you to narrow down what you're trying to achieve.

Harmonic analysis of the historical time series of such data is a possibility.

Article Rainfall Variability and Rice Sustainability: An Evaluation ...

Rainfall Variability and Rice Sustainability: An Evaluation Study of Two Distinct Rice-Growing Ecosystems

You can go for SPEI and SPI