Dry Weather
Drought
noun
Remember how 天気 is weather (and how 天 often refers to sky things?). Well, when those sky things are dry, you have dry weather.
Note that 干天 is quite old-fashioned and you'll find it mainly in formal writing and advanced set expressions.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
この神社の池には、どんな干天でもゼッタイに水があったんだって。
It's said that the pond at this shrine had water no matter what kind of dry weather there was.
こちらでは、今までの干天がウソのように、昨夜から急に大雨になっています。
Here, it suddenly started pouring rain last night, completely different from the dry weather we've had until now.
ここ最近ずっと干天だったせいか、川の水が流れてないんですよね。
Maybe it's because we've had a drought all these years, but the river is not flowing.