Blood rain is most likely just rain with fine sand particles in it, usually carried from the desert. It's quite common in warmer countries and is also occasionally seen in colder ones, in fact blood rain has been forecast for the UK quite soon.

There is no evidence that it harms people, animals or plants, perhaps because the particles are so small and it all washes away so quickly. In the past many people believed that blood rain was a bad omen, but this isn't because of anything bad that actually happened with it - it's just that if you don't know it's a natural phenomenon, it looks scary because it does seem as if blood is falling from the sky - and that made people think they were being punished by the heavens, or warned about something. But now that we know it's natural and harmless, many people find it quite interesting to see blood rain.