Giant ‘rivers in the sky’ – that can carry up to 15 times the amount of water in the Mississippi River – can virtually wipe out species when they dump vast amounts of rain over a short period, causing some of the world’s worst floods, according to new research.And the problem is set to get worse because of climate change, scientists warned. They found that 97 to 100 per cent of wild Olympia oysters in north San Francisco Bay died in 2011 after the region was hit by dramatic rainfall caused by atmospheric rivers.