| 英文摘要: | The summer of 2013 was the hottest on record in Eastern China. Severe extended heatwaves affected the most populous and economically developed part of China and caused substantial economic and societal impacts1. The estimated direct economic losses from the accompanying drought alone total 59 billion RMB (ref. 2). Summer (June–August) mean temperature in the region has increased by 0.82 °C since reliable observations were established in the 1950s, with the five hottest summers all occurring in the twenty-first century. It is challenging to attribute extreme events to causes3, 4, 5, 6. Nevertheless, quantifying the causes of such extreme summer heat and projecting its future likelihood is necessary to develop climate adaptation strategies7. We estimate that anthropogenic influence has caused a more than 60-fold increase in the likelihood of the extreme warm 2013 summer since the early 1950s, and project that similarly hot summers will become even more frequent in the future, with fully 50% of summers being hotter than the 2013 summer in two decades even under the moderate RCP4.5 emissions scenario. Without adaptation to reduce vulnerability to the effects of extreme heat, this would imply a rapid increase in risks from extreme summer heat to Eastern China. The 2013 summer was characterized by long-lasting and widespread heatwaves and severe drought in Eastern China, especially in the Yangtze River Valley (Supplementary Fig. 2); the average number of heatwave days (daily maximum temperature of 35 °C or more) was at a historical high of 31 days, more than twice the 1955–1984 long-term average, affecting over nine provinces with a population of more than half a billion2. Preliminary reports indicate impacts on human health, agriculture and energy demand for cooling1, which is being used increasingly in China’s rapidly growing urban areas. The five hottest summers in Eastern China’s observed record over the past six decades have all occurred since 2000—in 2013, 2007, 2000, 2010 and 2011—with 2013 and 2007 summer temperatures being the hottest, at 1.1 °C and 1.0 °C above the 1955–1984 30-year average (Fig. 1). There is also a clear connection between summer heat and precipitation deficit; summer mean temperature and total precipitation are significantly negatively correlated at the local scale (Supplementary Fig. 3) and large negative precipitation anomalies are observed in the areas hit hardest by the 2013 summer heat (Supplementary Fig. 4). The recent frequent occurrence of hot summers and the unprecedented heat of the 2013 summer inevitably raises questions about whether and to what extent anthropogenic climate change has affected the intensity and frequency of occurrence of extremely hot summers in Eastern China and whether they will increase further in the future as anthropogenic climate influence continues to strengthen.
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