Malbim on Job 38:26

להמטיר, וכן ערך את ירידת המטר שלא ירד המטר תמיד במקום שעלו האדים משם, כי רוב האדים עולים ממקום ישוב ששם יש צמחים ובע"ח המפיקים אדים, או מן המים, וה' ערך שהמטר ירד גם במדבר, וזה או לפורעניות כמ"ש בר"ה שאם נגזרו גשמים בר"ה והעם לא זכו יורידם אל המדברות, וז"ש להמטיר על ארץ לא איש, או שהוא לטובה, כדי. Rain falling on desolate land can be a blessing or a waste depending on the circumstances; this provides more opportunities for Providence.
Sometimes for good? For example, if the people of Israel were absolutely wicked on Rosh Hashana [the annual Day of Judgment] and meager rainfall was prescribed for them but they subsequently repented. Their allotment could not be increased, for the decree has already been ordained. However, the Holy One, Blessed be He, then makes it rain at the right time and where it is needed, all in accordance with the condition of the land. Sometimes for bad? For example, if the people of Israel were absolutely righteous on Rosh Hashana and bounteous rainfall was prescribed for them but they then change their ways. The allotment could not be decreased for the decree has already been ordained. However, the Holy One, Blessed be He, then makes it rain at the wrong time and where it is not needed (TB Rosh Hashana 17b).