As Japan’s concrete jungles sizzle, urban forestry offers an all-natural fix

On a scorching day in Tokyo last Sunday, residents took to the streets to measure the temperature. The Japan Meteorological Agency recorded a high of 35.3 degrees Celsius, but temperatures varied greatly depending on their surroundings. Under the shade of a mountain cherry tree near Nakano Station, the temperature was slightly higher at 37 C. However, an asphalt road just outside the shaded area registered an alarming 44.5 C. Street temperatures can soar even higher, reaching 46.7 C at shoulder height.

Sumiko Sasamoto, a member of a grassroots group focused on increasing tree cover in the ward, noted that while weather forecasts often predict temperatures around 35 C or 36 C, many areas are actually experiencing much hotter conditions. Later, in a shaded area lined with Japanese white oak trees, temperatures were in the 36 C range even at 50 cm and 130 cm heights, feeling cooler due to good wind circulation.

Urban greening is crucial in mitigating the effects of urbanization and climate change, but tree canopy cover in Tokyo's central 23 wards has declined from 9.2% in 2013 to 7.3% in 2022. Tokyo's tree canopy cover is considerably lower than other global cities such as New York, Paris, Barcelona, and Melbourne. While Japan has yet to adopt numerical tree canopy cover targets, urban trees provide numerous benefits including cooling through shade, reducing stormwater runoff, improving water quality, and offering therapeutic effects through forest bathing.

However, the tree canopy is decreasing, with tree cover on public land falling by 38% and on private land by 57% in the past decade. Residential areas saw the highest percentage of tree cover loss, and many old houses with large gardens are losing trees due to the high inheritance tax rate and the trend of selling land.