Gravity makes raindrops fall vertically in the form of free fall, and wind makes raindrops move in a straight line at a constant speed in the horizontal direction. When the wind speed is high, the wind pushes the raindrops harder, and the acceleration and speed increase.
The falling speed of raindrops is the sum of the horizontal and vertical speeds of raindrops, which just forms a right triangle with the horizontal and vertical speeds and is the hypotenuse of this right triangle.
The vertical velocity component is a free-falling motion, and the greater the horizontal velocity component, that is, the longer the right angle side and the larger the oblique side, that is, the greater the falling speed of raindrops.