Heatstroke Gap: Cool Regions Faced Higher Risk Than Warm Ones

What We Found

Heatstroke risk in cool regions is about twice that in warm ones. On days when the high reached 35°C, cooler areas saw roughly 2 emergency transports per 100,000 people, compared with about 1 in warmer regions.

Why It Matters

Japan uses a single nationwide threshold for heat alerts, but risk is not the same everywhere. People who live in cooler climates are less used to extreme heat and often have homes and communities that are less prepared for it—so a sudden spike can hit harder.

The findings suggest heat alerts should be more local—a challenge not just in Japan, but also in northern Europe, Canada, and northern U.S. states, where historically cool regions now see record heat.

Visual Highlight

Cool zones (<22°C summer average) show nearly double the heatstroke incidence at the same daily temperature.

How We Did It

Dataset & Approach

• Emergency transport records for 790,000 heatstroke cases (2008–2022).
• Daily temperature and humidity from each prefectural capital.
• Population data and a simple three-way climate grouping based on average summer temperature.
• Tested several climate and demographic variables; summer average temperature explained regional differences best.

Validation

The choice of variables and the framing of the findings were reviewed with a climate reporter, and a university epidemiologist checked that the patterns matched what is known about how the human body adapts to heat.

My Role

• Led the data analysis for the project, building the full R workflow for cleaning, modeling, and visualization of nationwide heatstroke data.
• Tested multiple explanatory variables and identified summer average temperature as the most robust and interpretable predictor of regional heatstroke risk.
• Reported and wrote the data analysis section of the front-page article, translating statistical results into clear explanations for readers.
• Collaborated with a climate reporter to link the statistical patterns to on-the-ground reporting.
• Coordinated expert review with a university epidemiologist to confirm the interpretation of the findings.

Impact & Publication

• A front-page investigation in The Asahi Shimbun that spotlighted northern risk and helped push discussion on region-specific heat alerts.