Climate Data Processing and Heat Stress Indices in Japan

This dataset is derived from daily meteorological observations and provides summer (June–August) annual aggregates and associated heat stress indices for stations across Japan from 1981 to 2024. The original daily data were downloaded and processed using the provided R scripts. These scripts perform quality control, variable derivation, and aggregation to station-level summer means, forming the basis for all subsequent analyses. The dataset includes both observed and counterfactual estimates of relative humidity (RH) and heat stress indices, enabling attribution of humidity-driven changes in heat stress under recent climate conditions. The counterfactual scenario isolates the thermodynamic contribution to atmospheric moisture changes by removing the residual (non-thermodynamic) component of RH variability, allowing quantitative assessment of the role of humidity in amplifying heat stress. The dataset supports the findings of : [Heat-Stress Indices Worsened by Recent Humidity Increase in Japan] (under review / in preparation)