Why does the Christian god create evil and/or catastrophes?  ?

Actually, that verse probably uses the definition of evil that means any inconvenient or unpleasant thing.  Of course he does not create evil in the way we understand it today.

Isaiah 45:7

"I form the light, and create darkness: I make peace, and create evil: I the Lord do all these things."

God did not create evil. It is a word that was translated from the Hebrew inadequately.

Isaiah 45:7 puts forth opposites. Darkness is the opposite of light.

Evil is not the opposite of peace. The Hebrew word translated "peace" is shâlôm, Râ‛âh, the Hebrew word translated "evil" in the KJV means adversity or calamity.

Calamity is a better meaning of the word than evil.

God creates calamity to correct His children as a warning to stop doing what is wrong and start doing what is right.

if you stay as innocent as you're you don't need to worry about that.

He creates them to try and change men's hearts so they would return to Him. The Great Tribulation is like that,the end of the world is coming and god is giving it one last go at it to try and change the hardened wicked heart of man so they would come to Him in repentance and be saved. 

The passage you quote is better translated "...I make peace, and create consequences..." for those that are disruptive, thwart God's will, and are sinful and evil, God has created consequences for their evil deeds. 

Evil was an Agel creation when some rejected the Love of God, sometimes God allows a Catastrophe to take a grater good out of it

Because that mythical character is a murderous psycho.

God does not create evil or catastrophes.  The author of Isaiah is attributing this to God anyways, as any ancient Near Eastern culture would to their deity.  That is the best they could understand the penultimate revelation of his character that God gave them at that time and God accommodates their understanding.

  In the ultimate revelation of his character, as revealed by Jesus, God shows he is incapable of anything but love.

And there is calamity in the NKJ.  The context in v. 1 is about "Cyrus" and he is to be used as God's instrument in Chapter 45 of Isaiah, for the specific reasons expressed in that narrative.  If you still have a problem with that, then take it up with Cyrus!

The idea of Satan as a distinct God hadn't yet occurred at the time that was written. Same reason why it's only towards the end that the afterlife is mentioned.