Using perlin noise is a really interesting way to create wonderful natural effects. p5.js has plenty of examples of this, such as here:

https://p5js.org/examples/math-noise-wave.html

I'd also really recommend Daniel Shiffman's tutorials on the subject:

https://www.youtube.com/watch?v=Qf4dIN99e2w

See the Pen perlin for mcclymont.co by amcc (@amcc) on CodePen.