Neutral term for rain or precipitation, often used in weather forecasts and reports.
Rainfall is expected over a wide area tomorrow.
The amount of rainfall is less than average.
There is a lot of rainfall in this region during the summer.
It has been raining continuously since yesterday.
We were hit by heavy rainfall during the match.
降雨 is a formal, written term used in weather reports and technical contexts, while 雨が降る is the natural everyday phrase for saying it is raining.
降雨 is a formal, technical term for rainfall used in scientific or official weather reports, whereas 雨降り is the everyday word for rainy weather.
降雨 refers to rainfall, while 降雪 refers to snowfall; the two are easily confused because of their parallel formal structure.
Compound of 降 (descend, fall) and 雨 (rain). The reading is on'yomi.