Does anyone have any thoughts on the use of these methods and when both might be used to explore trends in the data.
I think most people who sample monthly, quarterly or biannually would jump straight into using the Seasonal Mann-Kendall test but I think both tests can provide useful information.
For example, I used the Mann-Kendall test to evaluate trends in monthly groundwater levels. This revealed information about the behavior of trends that would not be apparent using the seasonal kendall test. Because each month is evaluated separately you can assess and compare changes across each season. In my case this revealed summer groundwater levels are declining faster than winter. I also observed a far greater number of trend detection over summer months.
The pattern in trend detection and rates of decline are almost certainly linked to increased irrigation over time during summer periods. However, evaluating monthly trends separately reduces the power of the tests, this is where the collective assessment of the seasons is useful for testing the statistical significance of the trend. Therefore I think much can be added by performing both tests where applicable.
I'd appreciate your thoughts?