The People of Sparks by Jeanne DuPrau

When teenagers Lina Mayfleet and Doon Harrow lead their people up out of the Earth, fleeing their dying underground city of Ember, everything is new and a little frightening to the refugees--the sun and the moon, birds, trees, fire…and the people of Ember are strange to the 322 citizens of Sparks, one of the few towns on Earth to survive the time of The Disaster. How can they feed and house the 400 Emberites, the leaders of Sparks wonder, when they have just begun to be able to feed themselves comfortably? But if they don’t, these underground people with no survival skills will surely die in the wastelands. They take them in as best they can, but grumbling and bad feeling grows on both sides.