The God of the Old Testament is the same as the God of the New Testament. Therefore we need to maintain a unified view of God (who is immutable).
In the OT we see God bringing His wrath to bear upon His enemies, and the enemies of Israel, and also destroying the world with the Flood because of sin and evil. But since the coming of Christ, God is offering grace, mercy, and pardon to humanity, AND HOLDING HIS WRATH IN ABEYANCE. We are presently in the Age of Grace, the Gospel Age, and the Church Age.
But we also see that during the Tribulation and Great Tribulation, God will once again unleash His wrath against evildoers and enemies of God and Christ. And the wrath of God will also be the wrath of the Lamb.