Frequently Asked Questions
What is rainfall depth?
Rainfall depth is the vertical accumulation of precipitation on a flat, horizontal, impermeable surface over a defined period. 1 mm of rainfall = 1 litre of water per square metre (1 L/m²).
How does mm of rain convert to m³ per hectare?
1 mm of rainfall on 1 hectare (10,000 m²) equals 10,000 litres, or 10 m³. This relationship is critical for irrigation scheduling and catchment management.
What is an inch of rain?
1 inch of rainfall = 25.4 mm. In the US system, 1 inch of rain falls on 1 acre = 102,789 litres ≈ 27,154 US gallons, or 0.0833 acre-feet.
Why is rainfall measured in mm and not volume?
Depth (mm/inches) is used because it is area-independent — 10 mm of rain delivers the same volume per unit area regardless of the size of the basin, making comparisons straightforward.
How much water does a 25 mm rain event bring to a 1 ha field?
25 mm × 10,000 m² = 250,000 litres = 250 m³. At a bulk density of approximately 1 kg/L, this is 250 tonnes of water on one hectare.