Trend analysis of Rainfall

Question

I has rainfall data for which I did linear trend analysis using parametric test for various seasons.
In one season for example, I got slope 6.1 mm/decade and p value 0.0001. while for the other seasons I got slope 4.5 mm/decade and p value=.90. slope indicate that both the data has the trend. One is statistically significant and other not.
My question is, why I am saying to one has trend and other has not? And when both has such high slope why one giving significance result and other not??

Martin O'Rourke · Accepted Answer

Try plotting the rainfall data as a cumulative deviation from the mean. You will see that the rainfall has wetter and drier periods over time. This is normal. Rainfall is not uniform across time it does vary and you need to compare the whole data set.

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