multi-annual mean

Arithmetic mean of the occurrences, over a number of years, of a hydrological quantity associated with a given date or period within the year. e.g. Multi-annual mean monthly discharge for April is the arithmetic mean of all April monthly mean discharges for a number of years. (In contrast, monthly mean discharge (m3 s-1) is the volume (m3) of streamflow in a month divided by the number of seconds in that month.)

Terms of Hydrology