Irrigation is the watering of land to make it ready for agriculture. If you want to start a strawberry farm in the desert, irrigation will be necessary.
Irrigation comes from the Latin for "moist" or "wet," but it means the purposeful wetting of something. We wouldn’t really say that a storm provides irrigation (unless we were poetically trying to personify the storm). Irrigation systems are often complex combinations of canals, channels, and hoses. The word irrigation is also used in medicine to describe the process of washing out a wound before dressing it.