Temporal changes in mortality impacts of heat wave and cold spell in Korea and Japan.

Investigating how well people adapt to heat waves and cold spells has been an important issue under climate change. Also, most of previous studies focused only on the mortality risks for heat waves or cold spells for certain time period not considering its temporal changes and increasing frequencies. This study investigated the change in risks of mortality from heat waves and cold spells over time, and estimated the temporal changes in mortality burden attributed to heat waves and cold spells in Korea and Japan. We collected time-series data covering mortality and weather variables from 53 communities in the two countries from 1992 to 2015. Two-stage time-series regression with a time-varying distributed lag model and meta-analysis was used to assess the impacts of heat waves and cold spells by period (1990s, 2000s, and 2010s). In total population, the risks of heat waves have decreased over time; however their mortality burden increased in the 2010s compared to the 2000s with increasing frequency. On the other hand, the risk and health burden of cold spells have increased over the decades. Our findings showed that the future mortality burden of heat waves and cold spells might not decrease, when considering their changes in risks and frequencies.