One inch of rain refers to the depth of rainwater that would accumulate on a flat, impermeable surface if none of it evaporated, soaked into the ground, or ran off. It is a standard measurement used in meteorology to quantify precipitation.
To put it simply, if you were to place a rain gauge in an open area and it collected one inch of water after a rainfall, that means one inch of rain has fallen. This measurement helps in understanding the amount of water that has been delivered to a specific area, which is crucial for agriculture, hydrology, and weather forecasting.
For example, one inch of rain over one acre of land equates to about 27,154 gallons of water. This can help farmers determine irrigation needs or help city planners manage water resources effectively.