'If it rains, then the drought will end. The drought has ended. Therefore, it rained.' This commits which kind of fallacy?

Concluding that it rained because the drought ended is a formal fallacy, the fallacy of affirming the consequent.

The conditional says if it rains then the drought ends, so rain is sufficient for the drought ending.

The drought ending does not guarantee rain, since other causes could end it.

Inferring the antecedent from the affirmed consequent breaks a rule of valid conditional form.

The defect lies in the logical structure itself, which makes it a formal fallacy.