降雨 is read as こうう (kouu) and means rainfall.
こうう
kouu
じんこうこうう
artificial rain
こううりょう
amount of rainfall
こううりん
rainforest
あめふり
rainfall
あめがふる
to rain
あめのふるひはてんきがわるい
water is wet
あめふりばな
flower that is said to cause rain if picked (convolvulus, etc.)
あめのふる
rainy
ねこがかおをあらうとあめがふる
if a cat washes its face, rain is coming
ねこみみをあらうとあめがふる
if a cat washes its ears, rain is coming
こどもさわげばあめがふる
if the kids make a racket outside, there will be rain
あめふってじかたまる
adversity strengthens the foundations