1. Graduate School of Global Environmental Studies, Kyoto University, C-1 Nishikyo, Kyoto, Japan E-mail: echigo@urban.env.kyoto-u.ac.jp
2. Department of Civil and Environmental Engineering, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon Hong Kong, China E-mail: xiangru@ust.hk
3. Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Ave, Urbana IL, 61801, USA