Here's some information from the June issue of the SHISEI-DAYORI (City info):

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When earth and sand absorb too much rain water, landslides are likely to occur. Quite a few instances of massive mudslides happened in the past even after the rain had stopped.
Stay aware of the weather forecast and of the evacuation information released by the city government. Evacuate as early as possible to protect yourself.
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For more information go to the complete post on the Kumamoto International Foundation website:

http://www.kumamoto-if.or.jp/topics/topics_detail.asp?PageID=5&ID=7844&pg=1&sort=0&LC=e

This English page is a translation of the original Japanese announcement. The page contains a link to the Japanese in case you would like to check the translation or would like to share the same information with a Japanese person. There is also a link to a new website made by Kumamoto Prefecture that provides information, using Google maps, about areas that are at risk for mudslides, etc. The image you see on this post is of one of the maps. I think the information is valuable, but there are two problems. First, the site is only in Japanese. Second, even if you are able to read Japanese, if is very difficult to figure out how to interpret the information because the website does not provide detailed explanations, even in Japanese. I hope the prefecture will take steps in the future to fix these problems.