Spatial and temporal variations of regional high temperature events in China

An objective identification technique is applied to identify Regional High Temperature Events (RHTE) in China using daily maximum temperature data at 642 stations from 1961 to 2010. There are 213 RHTE identified. These events in general occur from May to September, with months from June to August being high season and the peak frequency appearing in July. Over the space, these events mainly occur in regions east of 90 degrees E, with higher frequencies and stronger intensities in the middle and lower valleys of the Yangtze River. Extreme and severe RHTE are more frequent in southern, central and eastern China and are less frequent in northern China. Statistics that characterize the regional events including annual frequency, annual sum of integrated index, annual sum of single indices (e. g. duration, accumulated high temperature intensity, accumulated impacted area and extreme high temperature) and annual maximum values of these single indices suggest that the RHTE are becoming more severe in both space and time and impacting more areas. A further analysis shows that the distribution patterns of the trend change of China RHTE, i.e. RHTE becoming more frequent and stronger in most China especially in northern China, but less frequent and weaker in eastern regions between the Yangtze River and the Yellow River during the past 50 years, is mainly a regional response to global warming. Meanwhile, the increasing trends in frequency and accumulated intensity of the RHTE in southern China may also be partly due to the western Pacific subtropical high westward extension and intensification in summer during the past decades.