Researchers have reported that countries that have a higher precipitation level also have higher autism rates. The reasons could be increased pollutants carried by precipitation, increased television viewing due to bad weather, or a lack of vitamin D due to staying indoors.
Sean Nicholson, a Cornell University policy analyst and an author of the study said, "If it rains a lot, children spend more times inside. It could be that there was something positive outside that they're getting less of, or there's something in the indoor environment that's harmful."