decrease vs change magnitude

decrease is a noun but change magnitude is not a noun.

Word	Noun	Adjective	Verb	Adverb
decrease	Yes	No	Yes	No
change magnitude	No	No	Yes	No

As verbs, change magnitude is a hypernym of decrease; that is, change magnitude is a word with a broader meaning than decrease:

decrease (noun)	change magnitude (noun)
the act of decreasing or reducing something
the amount by which something decreases
a change downward
a process of becoming smaller or shorter

decrease (verb)	change magnitude (verb)
decrease in size, extent, or range	change in size or magnitude
make become smaller