I haven't really worried about it personally........ Let me clarify by saying there are two different definitions of triggers in this situation - being personally alerted due to motion on a camera, and
Blue Iris triggering recording due to movement.
I don't care if Blue Iris ends up recording more because rain is causing the recording trigger to occur more frequently. It uses more storage space, but hard drives are big and cheap now so storage really shouldn't be an issue. I'd rather error on the side of having too much recorded than trying to filter out rain in my recording trigger and accidentally miss an important event.
Then you have the situation of being personally alerted to motion via a text/email/etc. The only camera I have that actually sends alerts (via text) to me is my doorbell camera and it is set back under cover and not affected by the rain. I have also set it up so the camera records on any perceived motion (again I'd rather record too much than too little), but it only sends a text alert when a person is within about 2' of the door, so it wouldn't trigger in rain even if it wasn't under cover.
However, if I was getting a lot of false alerts/texts on my phone, etc I might change it by trying these things......
1) Camera installation makes a big difference. The farther back your camera is from the actual rain, the less it is going to trigger on rain. This is because rain drops that are 6" away from the camera appear much smaller than rain drops that are 6mm away from the camera. So anytime you can get the camera under cover is a good thing.
2) Look into creating a new profile that is for rainy times. Increase the notification alert thresholds on your cameras so they don't trigger as much, or even just have the cameras constantly record and not send out alerts at all. I wouldn't worry about trying to find a way to automatically set this profile. You can always get into your system and manually change to the rain profile when you start getting those false rain alerts.
This means I will have more recorded footage to review if there is some event that I need to document. But for me personally, the odds of having any event is pretty small, and then to have that event be in the rain is even smaller. I'll just get through the footage manually when/if I have to.
Hopefully that makes sense.