Abstract
Global warming causes a temperature rise and alteration of other meteorological variables that directly or indirectly affect human comfort. The wet bulb globe temperature (WBGT) incorporates the effects of multiple meteorological variables to provide a reliable measure of human thermal stress. Despite the large significance of WBGT on public health, studies related to characterization and trends assessment of WBGT are limited in the tropical humid region like Peninsular Malaysia due to the unavailability of all meteorological variables required for such analysis. This study employed reanalysis meteorological data of ERA5 to assess the characteristics and changes in hourly, daily, monthly, seasonal and annual outdoor WBGT over peninsular Malaysia for the period 1959-2021 using the Liljegren method. The WBGT values were classified into five categories to assess the human thermal stress levels defined by the United States Department of the Army (USDA). The mean daily WBGT in PM varies from 21.5 degrees C in the central south elevated region to 30.5 degrees C in the western coastal region. It always reaches a heat-related illness risk level (31.20 degrees C) in the afternoon during monsoon and extreme stress conditions during inter-monsoonal periods. The trend analysis revealed an increase in WBGT for all the time scales. The higher increase in the mean and maximum WBGT was estimated in the coastal and south regions, nearly by 0.10 to 0.25 degrees C/decade. The increase in mean nighttime WBGT was 0.24 degrees C/decade, while in mean daytime WBGT was 0.11 degrees C/decade. The increase in WBGT caused a gradual expansion of areas experiencing daily WBGT exceeding a high-risk level for 5 h (11 AM to 3 PM). The information and maps generated in this study can be used for mitigation planning of heat-related stress risk in PM, where temperature extremes have grown rapidly in recent years.