I'm trying to find some information about the Mann-Kendall trend test. I've tried to make some research on google but the main reference that I find is the 1976 book "Rank correlation methods" by Kendall. Obviously this book isn't easy to find so I hope that you could give some links to find some practical information about it
It's also known just as the Mann test. I find it in Nonparametric Statistical Methods, Hollander and Wolfe, and a discussion of its power in The Power of Statistical Tests for Trend Detection. It's in the R package Kendall.
Hopefully, this will be enough to get you going.