Perhaps the answer is in the explanation (I think from Rashi) of the idea of geshomim beitom. What is the special blessing of beitom? That it should not fall when it would be an interruption or a hardship, but rather when it will be the least disruptive (Erev Shabbos) and most useful (rain that falls during the day, especially in arid climates, evaporates quicker and is less useful).
HKBH created a “water cycle” that operates as he directs, but within the parameters of wind, weather, climate, and temperature that he set as its boundaries. Within those boundaries there can be variation, unless he directly determines (geshomim beitom) when and how the rain falls. It is in this interaction within the cycle that he set in motion that we see he holds the keys.