The Here and Now, by Ann Brashares (Delacorte Press, YA, April 2014).
It is a bad future. Messed up climate. Plauges. Scarcity. Death from plagues. Hopelessness....But no, there is hope! With the help of newly perfected time travel, the future can be ameliorated!
Except that a whole bunch of time travelers arrive in our United States and don't actually want to mess anything up--they are too busy not being in the bad future. And to make sure that their comfy present isn't jeopardized, the leaders of the time travelers make it their priority to enforce Rules, in a nasty, private little dystopia way of their own.
Our heroine, Prenna, is a traveller from the future and after a few years crash course in "passing" she is a (still an odd-ballish) high school student. Our hero, Ethan, is a normal enough high school boy...who saw her arrive (though she doesn't remember it), and won't stop being her friend. Even though close contact with the natives is one of the things forbidden to Prenna....
And so things would have gone on uneventfully enough, with Prenna pushing at the rules, and Ethan pushing at her differences (in a nice way--I like Ethan) except that......
There are other time travelers. And not everyone wants one-way trip to the past to be just a staycation. Some want to change it. And one such man tells Prenna secrets she was never supposed to learn. What he tells her sends Prenna and Ethan fleeing from the time traveler community to try to save the future....and to enjoy as deeply as possible being together in the present they're about to try to change, for as long as they can.
So although this might seem like Romance Time Travel, there's actually a lot more too it. It's also Stranger in a Strange Land time travel, and two people from different places trying to connect story, and young person questioning assumptions story, as well as two people falling in love and exploring all of that together, and it's really quite interesting once it all gets going. Not paradigm-shifting interesting of a deeply moving kind, but a good read.
It is, however, not desperately fast to get going--I really truly didn't need to be told with quite so heavy a hand how Ethan understood Prenna. And the time travel paradoxes make me a bit nervous--Ethan and Prenna really do change time so that the future is different, which should mean Prenna not being Prenna....but sometimes, when reading travel, "whatever" is the best way to simply enjoy a good story.
And it is not one I would give to the sci fi/speculative fiction fan; it's more one, I think, for the high school relationship fan who wants something with a bit of a twist (that doesn't involve vampires). It doesn't have the full on, gritty, really high stakes feel of a full-blown dystopia; it's more a story using speculative fiction elements to get to the relationship between the two main characters. To like the story, you have to like Prenna and Ethan, and kind of let the glimpses of the future and the action in the present just carry you along.
So sort of a restful, escapist, romantic spec. fic. with dystopian elements, good for beach reading.