In the paper some methods for identification of the monotonic deterministic trend in hydrological time series were presented and discussed: the t-test, the Mann-Kendall test with corrections, the Theil-Sen estimator with the test based on bootstrap and the prewhitening method. The tests varied in assumptions on the existence of the serial correlation and the distribution of the variables in the series. Occasionally, when assumptions were not fulfilled, the tests led to contradictory conclusions. As examples, the applications to annual maximum and minimum flows were presented.

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