Projected changes in mild weather frequency over China under a warmer climate

Abstract

Previous studies have largely focussed on changes in mean climate state and climate extremes under a warmer climate, and little is known about changes in mild weather, which is a positive and pleasant condition and is highly related to human outdoor activities. Although changes in observed mild weather frequency over China, and their drivers, have been revealed, the understanding of how mild weather evolves with projected warming is still limited. Here, we examine future changes in mild weather frequency over China based on comprehensive thermal comfort indices, and dynamically downscaled climate projections produced by the Regional Climate Model version 4 within the framework of the Coordinated Regional Climate Downscaling Experiment—Coordinated Output for Regional Evaluations. We demonstrate that changes in mild weather frequency in a warmer future exhibit remarkable regional discrepancy. In particular, densely populated southeastern China will experience a robust decrease in mild weather relative to the current level, although a general increasing trend is observed in this area over recent decades. On a seasonal scale, the decrease in mild weather in summer overwhelms the increase in spring and autumn, and this is more prominent in warmer regions. Regarding the drivers, it is suggested that changes in mild weather frequency are dominated by elevated temperatures, with little contribution from relative humidity, wind speed, and sunshine duration.