Another item of information provided in the Qur'an about rain is that it is sent down to Earth in "due measure." This is mentioned in Surat az-Zukhruf as follows:
It is He Who sends down water in measured amounts from the sky by which We bring a dead land back to life. That is how you too will be raised [from the dead]. (Qur'an, 43:11). 
This measured quantity in rain has again been discovered by modern research.
Every year, the amount of water that evaporates and that falls back to the Earth in the form of rain is "constant": 513 trillion tons. This constant amount is declared in the Quran by the expression "sending down water in due measure from the sky." The constancy of this quantity is very important for the continuity of the ecological balance, and therefore, life.