Abstract
In this study, the variability and trends of the outdoor thermal discomfort index (DI) in the Kingdom of Saudi Arabia (KSA) were analyzed over the 39-year period of 1980-2018. The hourly DI was estimated based on air temperature and relative humidity data obtained from the next-generation global reanalysis from the European Center for Medium-Range Weather Forecasts and in-house high-resolution regional reanalysis generated using an assimilative Weather Research Forecast (WRF) model. The DI exceeds 28 degrees C, that is, the threshold for human discomfort, in all summer months (June to September) over most parts of the KSA due to a combination of consistently high temperatures and relative humidity. The DI is greater than 28 degrees C for 8-16 h over the western parts of KSA and north of the central Red Sea. A DI of >28 degrees C persistes for 7-9 h over the Red Sea and western KSA for 90% of summer days. The spatial extent and number of days with DI > 30 degrees C, that is, the threshold for severe human discomfort, are significantly lower than those with DI > 28 degrees C. Long-term trends in the number of days with DI > 28 degrees C indicate a reduced rate of increase or even a decrease over some parts of the southwestern KSA in recent decades (1999-2018). Areas with DI > 30 degrees C, in particular the northwestern regions of the Arabian Gulf and its adjoining regions, also showed improved comfort levels during recent decades. Significant increases in population and urbanization have been reported throughout the KSA during the study period. Analysis of five-years clinical data suggests a positive correlation between higher temperatures and humidity with heat-related deaths during the Hajj pilgrimage. The information provided herein is expected to aid national authorities and policymakers in developing necessary strategies to mitigate the exposure of humans to high levels of thermal discomfort in the KSA.
Plain Language Summary We analyzed the outdoor thermal discomfort using an in-house high-resolution reanalysis generated using an advanced Weather Research and Forecast modeling system and assimilating all available regional observations. We examined the spatiotemporal distribution of thermal discomfort from 1981 to 2018 over Kingdom of Saudi Arabia (KSA). Our results outline changes in livability conditions in terms of the trends of different thermal discomfort thresholds in the last four decades across KSA. Further, we investigate the possible reasons for the increase/decrease of thermal discomfort over different regions of KSA. Our study suggests improved living conditions over some parts of the northwestern Arabian Gulf and their adjoining regions in recent decades and worse conditions over the southeast regions. The detailed information provided here on the hotspots of improved or deteriorated human discomfort will be useful for decision makers to take efficient mitigation measures.