Future Changes in the Frequency and Duration of Extreme Winds in Japan — Focusing on the Risk of Low Wind Power Generation due to Strong Winds

Average wind speeds are projected to decrease annually, mainly in the Northern Hemisphere, owing to the progression of global warming. Although the momentum for the spread of offshore wind power generation is growing in Japan, the average surface wind speeds in the region are also decreasing, and wind resources are expected to decline in the future. However, the risk of low wind power generation due to wind conditions exists not only when the wind is weak, but also when the wind is strong. This study investigated future changes in the frequency and duration of extremely low and high winds around mainland Japan.

In this study, we used 2°C warming climate datasets (31 years × 12 members) and present climate datasets (31 years × 2 members) from the 5 km mesh downscaling data from the Database for Policy Decision-Making for Future Climate Change (d4PDF). The annual frequency of occurrence and maximum duration of weak (below cut-in wind speeds) and strong (above cut-out wind speeds) winds in the future (2°C warming) and present climates were compared in ensemble averages.

Under the present climate, weak wind events were more pronounced over land in summer, with a frequency of up to 70% and a maximum duration of approximately 96 h, depending on the location. Under future climate conditions, the weak wind trend will intensify further, increasing the frequency by up to 2.5% and the maximum duration by up to approximately 24 h. Under the present climate, strong-wind events were less conspicuous than weak-wind events and occurred mainly over the ocean in both summer and winter, with a frequency of up to 1–2% and a maximum duration of up to 12 h. In the future, the frequency will increase by approximately 1%, and the maximum duration will increase by approximately 6 h. The maximum duration of strong winds during the 31-year analysis period was approximately 48 and 60 h in summer and winter, respectively, under the present climate and increased by up to 24 h each under the future climate. Factors contributing to these changes include an increase in the number of strong typhoons, a decrease in movement speed in summer, and a shift in the Japan Sea cold air mass convergence zone (JPCZ) with strong northwesterly winds to the north in winter.

These findings suggest that under future climatic conditions, the probability of a long-term duration of extremely high winds will increase, potentially resulting in more severe low-generating events at offshore wind facilities than in the present climate.