I doubt very much that dryness has caused the joints to separate, Myrna. Individual pieces of wood for a table, unlike those in say, wood flooring, are glued together and there is always a seasonal fluctuation in moisture levels.
How is the table held together underneath? Slats with screws in them?
My guess is that these are stress fractures at the gluelines, probably caused by the effects of the Sun and possibly by the method used to attach the table to the legs.
If the boards have bowed then you're likely not going to get them back together again. Is it a round table or a rectangular/square one?
I'd wet a flannelette [sp?] sheet then put it thru the spin cycle to get rid of most of the moisture and then lay it over the table's surface. Of course, move the table out of the sun. Repeat as necessary to "close" up the gaps, then let it airdry once more, again, out of the sun.