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Paper short abstract

This paper examines rain gardens in Tokyo as devices that make legible the ecological accountability for flooding, heat, and water pollution visible in dry, impervious, and sanitized urban environments, while exposing the otherwise hidden and totalizing urban hydrological system.

Paper long abstract

This paper examines rain gardens (ameniwa) in contemporary Tokyo as a landscape intervention through which ecological accountability for flooding, heat, and water pollution has become legible in dry, impervious, and ecologically sterilized urban settings. Over the past decade, rain gardens have entered Japanese policy and design discourse through the translation of “Green Infrastructure” concepts and techniques developed by planners, engineers, and ecologists in Europe, North America, and Asia. Their appearance in Tokyo is linked to a broader national revaluation of flood management following the 2020 flooding of the Kuma River in Kumamoto, which fed into a prefecture-wide implementation of watershed-based flood control (ryūiki chisui). Within this shifting policy context, rain gardens have taken hold unevenly, appearing as DIY household installations, roadside bioswales, park-based projects, and corporate or municipal showcases.

Rain gardens function here as sentinels of ecological accountability: living, diagnostic devices that enable residents and practitioners to apprehend their position within an otherwise hidden and totalized urban network of water infrastructures and bureaucratic domains. Designing and maintaining a rain garden requires attention to how rainwater moves across impervious urban surfaces, through fragmented and buried sewage and flood-control systems, and into waters and wetlands that provide habitat for local fauna and flora. Built to perforate the urban surface, rain gardens translate rainfall and runoff, soil infiltration, heat, and ecological change into perceptible, everyday signs, cultivating awareness of how ordinary water use connects to urban flooding, combined sewer overflows, climatic stress, and downstream ecological effects.

The analysis draws on fieldwork with municipal officials, engineers, planners, and civil society actors in Tokyo—primarily in Suginami Ward—alongside research tracing the global circulation of rain garden concepts through policy and professional networks. Read against longer histories of Japanese water governance, and in dialogue with practitioners who compare rain gardens to earlier hydrological devices such as rice paddies and rock gardens, the paper treats these interventions as diagnostic rather than corrective. Rain gardens render visible the historical production and institutional fragmentation of accountability for urban water.