I was thinking (and this is just brainstorming, not telling anyone what to do) that the 'health' and exposure to rain could use a higher level of granularity. So, for example, there's 100 Health and then entering an area with would lower that by 0.1 per second, going higher as you continue to be in that rainy area. So the incentive is to not only avoid but also stay as little as possible, without being too punishing if you just get wet for a moment.
That being said, I just want to see what you come up with next. :)