In this study, we analyse trends of total column water vapour (TCWV) using multiple years of satellite observations and find, on the global average, an increase in the TCWV amount by about 0.21 % per year. Further investigations of the hydrological cycle reveal that the assumption of temporally invariant relative humidity is not always fulfilled and that the response of the global water vapour turnover time to global warming is 2 to 3 times higher than previously reported values.