Global warming is the answer.
As the earth gradually warms and melts the icecaps, it creates more water in the oceans. More water in the oceans along with higher temps, means more evaporation. More evaporation means more water in the atmosphere. More water in the atmosphere means more rain and snow on the earth. More rain and snow on the earth means more water in the rivers and the underground aquifers. More water and snow on earth gradually lowers the temps. Also, means more ice for the icecaps.
Hmmmm... What was the question again?
no no no as algore tells it, it will both flood the oceans and parch the deserts. and if we ask questions we are lower than a neanderthal’s knee.