1. Doctor, Graduate School of Science and Technology, Kumamoto Univ., Kumamoto City 860-8555, Japan (corresponding author).
2. Professor, Graduate School of Science and Technology, Kumamoto Univ., Kumamoto City 860-8555, Japan.
3. Post doctoral fellow, Dept. of Geography, Nipissing Univ., ON, Canada P1B 8L7.
4. Assistant Professor, Graduate School of Science and Technology, Kumamoto Univ., Kumamoto City 860-8555, Japan.