Unfortunately it is not ...
Published by Istvan Szamosvari, Environmental Impact Assessment Expert, Consultant at Aquaprofit Co.
Unfortunately it is not correct. Only a certain part of the rainfall is flowing into surface waters, that is characterized by runoff coefficient (a). The value of runoff coefficient is 0,90 for built-in areas (like cities, parking lots), and is around 0.05 in case of plains with natural land cover. Rather sue the following:
Q=α×I×t×A
where
Q: is the amount of flow
a: is the runoff coefficient
I: is the intensity of the rain
t: is the duration of the rain
A: is the catchment area
If you have only monthly amount of rain, You can use it instead of I×t part of the equation.
The runoff coefficient is to be calculated based on the different land-uses of the catchment area.