Answer:
1mm rainfall means every one square meter area is filled with the water of height 1mm. ... Take a vessel of 1 square meter in dimention and keep it in an open space during rain, you will be having 1mm height of water in it that is 1 litre of water in it at the end of the rain.
Similarly, 400 mm = 40 cm of water
Further ,all these calculations are made taking into consideration-:
no loss of water to the ground
no evaporation to the air &
the opening of rain gauge is neither partially blocked nor more open to air.
Step-by-step explanation:
We can safely say, 400 mms of rain means the height of the rain is 40cms above the ground in the area where rain pours.