I've got an intelligent humanoid species living on a planet very similar to Earth's. However, on this planet, rainstorms are more frequent and slightly... different. Each raindrop is at least an inch in diameter, making rainstorms more intense and creating some interesting design problems for the inhabitants.
How can I justify these raindrops being so much larger than the ones we find on Earth?
I'm looking for environmental or engineered conditions that can cause this, without manipulating universal constants like hydrogen-bond length. The surface of the planet is essentially identical to our own, with trees, animals, and an Earth-like landscape. It orbits within the star's habitable zone, but I haven't yet decided what the size/density/composition of the planet should be, so that's open to manipulation. The atmosphere density and composition are almost entirely mutable, but I'd like to keep the O2 concentration at about 20% to maintain my Earth-like lifeforms. All raindrops that reach the surface are in liquid or liquid-like form (no hail) and are larger than an inch in diameter. Typical rainfall during storms is highly variable, ranging between 5mm and 500mm per storm.