So I was thinking of a scifi setting where life evolves on a planet orbiting a star that periodically (every couple decades) hits the planet with a hemisphere-sterilizing CME.

So the plants respond by going for the "fire ecology" strategy where they stick a bunch of hardy spores under the soil deep enough to survive it, and sprout in the wake of the surface getting blasted.

but animals can't do that, and they can't afford to stick in one location, either. No matter where on the planet your species lives, eventually you'll get unlucky and your hemisphere is the one that gets wiped.

so they have to go for heavy r-selection breeding strategies: breed fast and don't expect many of your offspring to survive. Run fast and spread faster. Then there'll be enough of your species to survive when half of them get hit by a CME event

and what happens if a species evolves to sapients? Do they stick with r-selection? that's difficult to imagine for sapients.

Imagine a civilization that expects to lose a full half of their civilization every couple decades.

the alternative is that they switch to K-selection. They now have to value each life much more significantly. How do they handle the CMEs?

like I imagine they'd very quickly learn to observe their sun to try to and predict them, but I imagine they wouldn't be able to nail it down to which exact hour it'll happen.

And the planet keeps spinning.

and a 6 hour difference is the difference between losing south america and western europe and instead it hits asia and africa.

so the obvious solution would be that they would dig in.
If you can build shelters deep enough to keep from glowing when you come out, you could go hide underground when the CME comes

the other option is that you move your population. And that may be less realistic but I think it's a funnier and more interesting option

imagine the kind of mass transit infrastructure you'd need to have to periodically evacuate a hemisphere with only a few hours notice.

like imagine if we had to be ready to evacuate north and south america within five hours.
how would you even begin to approach that problem?

how many and how fast do your trains need to be to move 200 million people an hour?

although if I do some math, if the planet is the size of earth, you need to go mach 3 to get halfway around the planet in 5 hours.

That's gonna be a bit faster than a train.

That means you need 7 million concordes that go 50% faster.
Assuming they all take off at once. The longer the delay, the faster they'll need to fly.