Stronger diversification of human thermal stress conditions observed in low-income Asian countries

Abstract The day-to-day diversity of thermal conditions determines the range of human thermal sensation within a year, and its long-term shift affects thermal comfort demand with profound economic and public health implications. While previous studies have documented historical trends in specific thermal stress events regionally, such as heat waves and cold spells, how the temporal diversity of various thermal stress types has changed in response to climate change remains unexplored. Here, we present a practical and easy-to-use classification framework to characterize daily thermal conditions and then we use the Shannon’s index to quantify the diversity and its long-term shift over the past three decades (1990–2019). Using a high-spatial-resolution dataset of Universal Thermal Climate Index (UTCI) we developed for Asian regions, we quantify the diversity of daily thermal stress types and the population-weighted trends for each country in South, Southeast and East Asia. We find that human thermal stress conditions have become more diversified, especially in low-income tropical countries. This disproportionately stronger diversification in daily thermal stress types may worsen socio-economic inequity between wealthy and poor countries, posing great adaptation challenge for the latter.