To spell the word occurrence, why is the final consonant doubled before adding the suffix?

because the stress is on the second syllable of the base word ending in consonant + vowel + consonant

Explanation:

If a multiple-syllable word ends in a single consonant preceded by a single vowel and the accent is on the last syllable of the root word, double the final consonant before a suffix beginning with a vowel.

e. g. refer - referred, occur - occurrence, commit - committal, rebel - rebellion.

Answer: Because the end of the word occur is consonant + vowel + consonant.

Explanation:

When a word ends in consonant + vowel + consonant, we double the last consonant before adding a suffix.