I am conducting trend analysis on rainfall time series using the Mann-Kendall rank correlation coefficient (tau). I would like to also use another non-parametric test to increase the reliability of the results, but I am having trouble finding a suitable test.

I don't have a dataset that can be used for comparison purposed with the Mann-Whitney-Wilcoxon test, and I have read that the power of Spearman's rho test is almost identical to that of the Mann-Kendall test. I read that here: http://www.sciencedirect.com/science/article/pii/S0022169401005947

My rejection of the Spearman rho test is based on my understanding that an identical power makes the use of both tests invalid. Is this correct? If so, can anyone suggest another test I could use instead?

Ciara