Abstract:

Given the background of global warming, heatwave changes have attracted considerable attention: High temperature events not only cause severe drought, which greatly harms ecological vegetation and agricultural production, but also have a substantial effect on the production activities of water conservancy, industrial and mining enterprises, and human health: Xinjiang is one of the areas in China with a high incidence of extreme high temperature, and there have been frequent extreme high temperature events in this area in recent years: These events in Xinjiang have the characteristics of a wide range of influence, long duration, high outbreak intensity, and an early start and a late finish: The daily maximum temperature data are used to ascertain the heatwave changes in Xinjiang based on the quality-controlled station data from April to September of 1961 to 2018: Moreover, the NCEP reanalysis data and the sea surface temperature observations are employed to understand the potential reasons for heatwave changes: We have taken the temperature from 1981 to 2010 as the climatic mean: Our findings reveal that there was a significant increase in the number of heatwave days in Xinjiang under the local warming and wetting climate: This increase was more pronounced for extreme heatwaves (T_max ≥ 40 °C), whereas we found a decreasing trend for the occurrence of moderate heatwaves (37 °C > T_max ≥ 35 °C): We found that the first heatwave is beginning earlier than previously (mid-April at the earliest), and the last heatwave is finishing later than before (late September at the latest): The increase of heatwave is most pronounced in April; however, it makes a limited contribution to the total heatwave change: In North Xinjiang, the abrupt transition occurs earlier than does that in South Xinjiang: We further show that there is a strong correlation between circulation changes and the heatwave days in Xinjiang: When the 200 hPa geopotential height over Balkhash Lake and its surrounding areas is higher (lower) than normal, the number of heatwave days in Xinjiang is larger (smaller): The variation of 200 hPa geopotential height over Balkhash Lake and its surrounding areas can be traced back to anomalies in the sea surface temperature (SST) in the equatorial Atlantic: The South Asian High would control a larger area, from Balkhash Lake to Mongolia, when the equatorial Atlantic SST is higher, which could result in more heatwave days in Xinjiang: As the reasons for the delay of the initial high temperature of some stations with reduced high temperature days in Xinjiang and the mechanism of influence of SST on high temperature events in Xinjiang remain unclear, the above problems require further study.

Key words: heatwave days, heatwave strength grade, the first day of heatwave, the last day of heatwave, atmospheric circulation, Atlantic SST, Xinjiang