Nothing wrong with rain,you're right there.
Unfortunatly, to get storable power out of it, you need dams. Lots of them. You've just flooded alot of river valleys, and destroyed a vast area of habitat. Plus a few other little things, like shutting of the sediment supply to downstream., and preventing the fish from getting upstream to spawn.
Plus mountains tend to be the best place for them. Mountains have a strong tendancy to be seimically active. Lots of fun for downstream....

And as an addedbonus, do not build dams in tropical areas.They tend to create vast, shalllow lakes. Rotting vegitaition in the lakes puts out more CO2 than a dirty coal power plant of the same size.

A few dams are useful, but too many are not.