If God can make His Son into actual bread for us to eat, raise Him from the dead, send the Holy Spirit (with gifts of tongues, visions, the miraculous,) heal the sick of incurable diseases such as leprosy, walk on water, walk through walls (as Jesus did after the Resurrection), then God can do anything, and the impossible is not impossible to God, It is relatively easy for God to do anything as He is an infinite omniscient Creator.
You struggle with God causing the destruction of mankind in a world flood?
Read the book of Apocalypse in the bible, Jesus said world events are coming in which the good and evil alike will both perish under God’s justice because of the sin’s of mankind,
The bible says God causes rain to fall on both the just and the evil alike.
The book of Exodus shows God asking the Israelites to invade Palestine with Joshua and leave no pagan survivors living, neither women nor children.
God’s justice has come upon the world in many forms throughout history.
Our Lady of Fatima warned if the world did not convert and pray the rosary that World war II would happen.
It is not God’s will that we suffer like this, the sins of mankind earn this upon us.
In the Vatican approved apparition in Akita in Japan, Our Lady has warned: if the sin of abortion does not stop, fire will rain down from Heaven and wipe out a third of mankind.
In the Old Testament God told the Israelites: ‘I am offering you a blessing or a curse. A blessing if you should keep My Commandments, or a curse if you should break them.’ The Jews firmly believe all the times in history where there country was invaded by a foreign power was because the Jews forsook the Commandments.
Why does God send His justice?
The saints have nothing to fear in death for they will reach Heaven.
The sinners may convert at the very last moment.
In tragedy people often turn to God as the last resort, and amend their lives.
Jesus told Saint Faustina this lesson about God’s justice vs God’s mercy:
‘If a person converts and changes their ways and asks for My Mercy, I will move Heaven and Earth to help.’
‘My Justice is also a mercy, because many are the souls who turn from the Hands of My Justice and turn to the Hands of My Mercy.’
Meaning many are saved, or at least saved in the end when they repent because of a tragedy, and seek God.