Future Changes in Extreme Wind Speeds over Japan Based on a Large-Ensemble Climate Dataset

Amid growing concerns about the impacts of climate change on extreme events, estimating future changes in extreme wind speeds has become increasingly important for wind-resistant design. Regions such as Japan are affected by multiple types of strong wind-generating systems, including tropical cyclones and extratropical cyclones, which complicates the assessment of wind speed extremes. Despite this complexity, relatively few studies have comprehensively evaluated future changes in wind speed extremes in such multi-hazard environments.

In this study, we assess future changes in extreme wind speeds over Japan using large-ensemble climate model simulations. To ensure a robust evaluation of rare and high-impact events, we employ a dynamically downscaled dataset with a horizontal resolution of 5 km (d4PDF_5kmDDS_JP), derived from the Database for Policy Decision making for Future climate change (d4PDF). The dataset consists of multiple ensemble members, including 60-year historical simulations as well as future climate experiments under +2°C and +4°C global warming conditions. This large ensemble framework enables a statistically stable estimation of extreme wind characteristics.

Extreme value distributions of wind speed are estimated for each experiment and subsequently bias-corrected using surface observation to improve their reliability. Based on these corrected distributions, changes in wind speeds corresponding to specific return periods are quantified and compared across different warming experiments.

The results indicate that, in some regions of Japan, the 50-year return-period wind speed increases by approximately 10% under the +4°C warming experiment relative to the historical experiment. Further analysis suggests that the projected increase in extreme wind speeds is primarily attributable to enhanced wind intensity associated with tropical cyclones, rather than changes in other synoptic-scale systems.

These findings provide important insights into the future behavior of extreme winds in a multi-hazard environment and offer a practical basis for incorporating climate change considerations into wind-resistant design in Japan, particularly through the adjustment of design wind speeds and safety margins.