Observed Trends in Various Aspects of Heat Waves across China from 1961 to 2010

This study investigates changes in heat waves characteristics across China during 1961-2010. Using daily observations of maximum and minimum temperature selected from a dataset containing 756 stations across China in summertime (June-August) from 1961-2010, heat waves are defined based on combined thresholds of daily maximum temperature (Tmax) and minimum temperature (Tmin). Such definition takes both the meteorological extremity and influences on human body into consideration. Related indices, including number (HWN), day frequency (HWF), duration (HWD) and intensity (HWI) are used to quantify heat waves. Significantly increasing HWN, HWF, HWD and HWI were observed in most parts of China except for Huang-Huai region. Pertinent results reveal an intriguing feature that the severity of heat waves in northern parts of China is mainly ascribed to excessively high daily temperatures within limited duration, while the great heat stress of heat waves in southern parts is primarily attributed to long duration. Northern parts of China recorded larger increases of heat wave intensity, with the maximum trend above 3°C decade^-1. Southern parts of China witnessed greater increases of heat wave duration, with the largest lengthening trend over 1 day decade^-1. Albeit much-shorter lasting, severe HWs in northern parts of China may be comparable to or even stronger than their counterparts in southern parts from the perspective of intensity. In a warming climate, heat waves occurred more frequently, lasted longer, and became stronger and more humid in most parts of China. In addition to significant increases in duration and intensity, the identified HWs became more humid in North China, coastal regions along South China and the Yangtze River Valley. The spatial extent covered by heat waves has substantially expanded since 1960s. The regions covered by HWs have expanded sharply across China, especially in northern parts of China. Similar results can also be achieved in the analyses of severe HWs of longest duration and/or maximum intensity. The largest expansions in North China and Northeast China can reach 8% decade^-1. These systematic assessments of heat wave changes across China may shed some light on future adaptations to the warming climate.

 This study provides a thorough and systematic evaluation of heat wave changes in China. Derived results serve to narrow the gap between the understanding of heat wave changes in China and in other regions of the world.