The speed of falling rain is the same 10 m above ground as it is just before it hits the ground. What does this tell you about whether or not the rain encounters air resistance?
The rain must be encountering air resistance or it would accelerate.
The force of gravity will cause an acceleration unless there is another force to balance it. In this case the only other force must be from air resistance. Air resistance or drag is related to the speed of the object. When an object is moving fast enough that the force of gravity is equal to the resistance from drag we say that the object is traveling at terminal velocity.