Sign up for emergency alerts at this website: http://www.bousai-oita.jp/pc/index.html
How to sign up for phone alerts:
Send a blank email to firstname.lastname@example.org using an email address that goes to your phone. Scanning the QR code on the green button that says 登録・変更はこちら on the page above will simply download the address for you. This just means you wouldn't have to type it in manually.
Wait until you receive a reply.
The reply message will direct you to a website on your phone where you select which cities you want to receive alerts for.
That's about it.
**All instructions are in Japanese. If you need help registering, find someone to help you.
Quick Japanese Reference for Warnings and Evacuation
注 意 報 (ち ゅ う い ほ う, chuuihou) Advisory warning: people should be aware that a disaster may occur
警報 (けいほう, keihou) Disaster warning: for impending disaster or hazardous situation (urgent)