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中山間地域の流域における人・森林・気象災害の現状と関わり： 高山市大八賀川流域における豪雨・豪雪を事例として

永井 信^*1*2，丸谷靖幸^*3，斎藤 琢*^*2

^*1国立研究法人海洋研究開発機構・地球環境部門・地球表層システム研究センター 〒236-0001 神奈川県横浜市金沢区昭和町3173-25
^*2岐阜大学・流域圏科学研究センター 〒501-1193 岐阜市柳戸 1-1
^*3九州大学・大学院工学研究院環境社会部門 〒819-0395 福岡市西区元岡 744

Current conditions and relationships among human beings, forests, and weather disasters in a mesomountainous river basin: A case study of torrential rains and heavy snowfall in the Daihachiga River Basin in Takayama

NAGAI Shin^*1*2, Yasuyuki MARUYA^*3 and Taku M SAITOH^*2

^*1Earth Surface System Research Center, Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan
^*2River Basin Research Center, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
^*3Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

Abstract

In Japan, areas near rural settlements in hilly and mountainous regions are often called mesomountainous areas. The relationship between humans and the ecosystem in mesomountainous river basins in Japan has changed as these areas are increasingly confronted with the impacts of climate change (e.g., an increase in extreme and abnormal weather events). In this study, we reviewed current conditions and relationships among human beings, forests, and weather disasters in the Daihachiga River Basin in Takayama, Gifu Prefecture. Specifically, we looked at spatio-temporal changes in the weather and forests during torrential rain (July 2020) and heavy snow (17 December 2014) events that were described with the aid of continuous in-situ observations and social statistics by local authorities and scientists. However, in a mesomountainous river basin such as this, which is experiencing both population decline and increasing disaster risk, more detailed and labor-intensive online monitoring is required. With this need in mind, we summarized the usability of (1) observation data obtained from unmanned sensors; (2) advanced remote-sensing observations by drones and satellite sensors with high spatio-temporal resolution; and (3) information from citizens on the Internet (social sensing), for example, information gained through Google Trends, Twitter, and Mapillary. We identified the following three important tasks for future study: (1) integration and mapping of various observation data and information; (2) analysis and evaluation to connect past, present, and future; and (3) the identification of a future vision of the river basin that includes dialogue with relevant stakeholders.

Key Words : Daihachiga River Basin, extreme weather event, forest ecosystem, mesomountainous regions, remote sensing; social sensing

(Received December 2, 2020. Accepted February 12, 2021)