by Glenn A. Hodgkins et al., September 2017 in Journal of Hydrology

Trends in major-floods from 1204 sites in North America and Europe are assessed.

Trends based on counting exceedances of flood thresholds for groups of gauges.

The number of significant trends was about the number expected due to chance alone.

Changes in the frequency of major floods are dominated by multidecadal variability.

See also here