The key challenges in the Tokyo Water Conservation Forests initiative stem from managing a vast area of forest over a century, especially as urbanization around the Tama River increases. Ensuring the continuity of forest health and its filtration capacity, while also balancing the needs of surrounding communities and expanding the project into private land, requires sustained resources and coordination. The efforts to restore private lands and maintain low sedimentation in the Ogouchi Reservoir face challenges related to land ownership, funding, and continued volunteer engagement. Moreover, climate change and increased urbanization may intensify pressures on the forests' role in stabilizing the water cycle and preventing natural disasters like floods or droughts.

Outcomes

For over a century, TMBW has owned and nurtured more than 50% of the forestland located in the upstream area of the Tama River as a means of ensuring stable, high quality water supply to the megacity and stabilizing the water cycle to build natural resilience against droughts and floods (Bureau of Waterworks Tokyo Metropolitan Government, n.d.). The forest ranges across 30.9km from east to west and approximately 19.5km from south to north, extending from Okutama Town, Tokyo to Kosuge Village, Tabayama Village and Koshu City in the Yamanashi Prefecture and covering a total area of approximately 23,000 hectares (Bureau of Waterworks Tokyo Metropolitan Government, n.d.). The Water Conservation Forest itself is the equivalent of approximately 10% of Tokyo's total area and is the largest forest in the country that is owned by any water supply utility (Bureau of Waterworks Tokyo Metropolitan Government, n.d.). In addition to nurturing and protecting forestland in its own possession, TBMW has also engaged in the restoration and protection of private forestland. In 2002 TBMW established the Tama River Water Resources Forest Team, a team of volunteers to restore private forestland in the watershed and expand the reach of TBMW's water conservation activities. Additionally, TBMW is working on purchasing private forestland in order to manage it properly as part of the Water Conservation Forests (Bureau of Waterworks Tokyo Metropolitan Government, n.d.). Tokyo's Water Conservation Forests are indicative of a long-standing and ongoing effort to protect the city's key water resources. The Water Conservation Forests have yielded many positive outcomes, including providing more water of a higher quality to the megacity. Due to the forests' natural filtration capacities, exceedingly low sedimentation rates are present in the Ogouchi reservoir, amounting to only 3.2% in over 50 years of the reservoir's operation (Bureau of Waterworks Tokyo Metropolitan Government, n.d.). Furthermore, the forests function as a "green dam", building natural resilience for extreme events (i.e. droughts and flooding) and ensure stability in the region's hydrological cycle. Finally, the forests also provide environmental value by absorbing carbon dioxide and purifying the air in Tokyo's vicinity (Bureau of Waterworks Tokyo Metropolitan Government, n.d.). Ultimately, Tokyo's Water Conservation Forests are an example of long-term commitment to source-water protection and a successful, nature-based approach to water resources management.