Future projections of extreme temperature events in different sub-regions of China

Understanding the spatiotemporal evolution of extreme temperature events is critical to evaluate their influences in nature. Out of 28 general circulation models (GCMs) in the Coupled Model Inter-comparison Project phase 5, eight GCMs were selected to simulate changes of the six extreme temperature indices (ETIs) in China: warmest daily maximum temperature-TXx, warm days-TX90p, tropical days-TD30, coldest daily minimum temperature-TNn, cool nights-TN10p and frost days-FD0. Statistically downscaled daily maximum and minimum temperatures at 552 sites under representative concentration pathway (RCP) 4.5 and 8.5 scenarios were used. The modified Mann-Kendall method was used to detect the trends and their significances in ETIs. The Morlet wavelet basic function was used to investigate the main and quasi periods of the ETIs over the historical (1961–2000) and future (2001−2100) time stages. The results showed that FD0 and TN10p had decreasing trends, and TNn had increasing trends at more sites than decreasing trends. However, TD30, TX90p and TXx showed consistently increasing trends both during historical and future periods under the RCP4.5 and 8.5 scenarios. More sites had significant trends in the 6 ETIs during 2001–2100. The decreases in FD0 and TN10p reached 31.4 and 27.4 days during 2021–2060 and 42.6 and 29.7 days during 2061–2100, respectively. The increases in TNn, TD30, TX90p, and TXx reached 8.7 °C, 45.3 days, 41.6 days and 5.7 °C over 2021–2060 and 7.2 °C, 65.6 days, 62.4 days and 6.4 °C over 2061–2100, respectively. With respect to the averaged values for 552 sites, the primary periods of FD0, TN10p, TNn, TD30, TX90p and TXx were 8, 8, 8, 3, 3 and 10 years from 1961 to 2017 and 4, 4, 4, 2, 2 and 3 years under the RCP4.5 scenario from 2021 to 2100, respectively, whereas only TN10p and TNn had the 2- and 4-year periods under the RCP8.5 scenario. Differently from the averaged ETIs over China, more sites had longer periods from 1961 to 2017 to 2021–2100 under the RCP 4.5 or RCP 8.5 scenarios. This outcome meant that many sites had smaller fluctuations and less periodicity from 2021 to 2100 than from 1961 to 2017. The spatiotemporal changes in the ETIs may lead to the shifting of cultivation, variety adaptability and production for main crops in different sub-regions or climate zones. This research provides projected characteristics of extreme temperature events across China.