I like the story in this encounter of Superman with Swamp Thing. There’s apparently a disturbance in the area around Superman – an unnatural drought is sapping all of the water sources. It turns out that this Superman, coming from a different Earth, is somehow not in tune with this new Earth. The result is that he’s drawing more solar power from the sun and is causing the drought around him.
Swamp Thing fixes it by ingesting Superman and helping him move on from his previous experiences. In comics logic it makes him in tune with the current Earth and everything is good again. Personally, I just love how it touches his sorrow and feelings about leaving his previous Earth.
From – Superman Vol. 4 Annual 1