Studies based on the 10th (90th) percentiles as thresholds have been presented to assess moderate extremes in China and globally. However, there has been notably little research on the occurrences of high extremes of warm days and hot days (TX95p and TX99p) and cold nights and very cold nights (TN05p and TN01p), based on the 95th and 99th (5th and 1st) percentiles of the daily maximum (minimum) temperature data at a certain station in the period 1971-2000, which have more direct impacts on society and the ecosystem. The trends analyses of cool nights or warm days are based upon the hypothesis that expects a linear trend and no abrupt change. However, abrupt changes in the climate, especially in extreme temperatures, have been pointed to as a major threat to ecosystem services. This study demonstrates that (1) the mean frequencies of TX95p and TX99p increased by 1.80 day/10 year and 0.62 day/10 year, respectively, and that those of TN05p and TN01p decreased by 3.18 day/10 year and 1.01 day/10 year, respectively, in mainland China. Additionally, the TX95p and TX99p increased significantly by 50.42% and 58.21%, respectively, while the TN05p and TN01p of all of the stations decreased significantly by 83.76% and 76.48%, respectively. Finally, (2) the TX95p and TX99p trends underwent abrupt changes in the 1990s or 2000s, but the trends of TN05p and TN01p experienced abrupt changes in the late 1970s and early 1980s. After the abrupt change points, the trend of warm and hot days increased more rapidly than before in most regions, but the trend of cold days and very cold days decreased more slowly than before in most regions, which indicates a greater risk of heat waves in the future.

Changes in temperature extremes can be linked to mean temperature changes and variability. This study aims to quantify observed trends in mean and extreme temperature values and to analyse the relationship between mean and extreme temperatures in mainland China, based on daily data from 1960 to 2015. This is the first analysis undertaken of the relationship between mean and extreme temperatures in mainland China. Based on the 95th and 99th percentiles of daily T max and the 5th and 1st percentiles of daily T min , warm days (TX95p), hot days (TX99p), cold nights (TN05p), and very cold nights (TN01p) were defined. The results showed the following: (1) large increasing tendencies of TX95p and TX99p nearly all occurred in locations where mean temperature had substantially increased, and large decreasing tendencies of TN05p were more probably at locations of warming in mainland China; (2) the rise of mean temperature significantly increased the frequency of TX95p and TX99p, and decreased the frequency of TN05p, which indicates a simple shift of the entire distribution towards a warmer climate and greater potential risk of heat waves in the future. The likelihood of occurrence of TX95p and TX99p increased by about 3 and 1 day, respectively, and the occurrence of TN05p was reduced by about 4 days with a mean temperature increase of 1 ∘ C, but the occurrence of TN01p was hardly affected, indicating increased variability of T min temperatures; and (3) the mean and extreme temperatures increased with the urbanization rate in China, and advanced phenologies and unaffected frequency of very cold nights (TN01p) could pose more potential risk of frost and freeze injury to crops in China in the future.

Abstract. A few researches based on the 10th (90th) percentiles as thresholds had presented to assess moderate extremes in China. However, there has been very little research reported on the occurrences of high extremes warm days (TX95p and TX99p) and cold nights (TN05p and TN01p) according to 95th or 99th (5th or 1st) percentiles which has more directly impacts on society and ecosystem systems. The study showed: (1) the frequencies of TX95p and TX99p averagely increased by 1.80 days/10 a and 0.62 days/10 a respectively in all stations of mainland China, and TX95p in 50.42 % and TX99p in 58.21 % of the stations increased significantly, but TN05p in 83.76 % and TN01p in 76.48 % of stations decreased significantly, and the frequencies of TN05p and TN01p averagely decreased by 3.18 days/10 a and 1.01 days/10 a respectively in all stations, (2) except in Central China, other regions of China showed an increasing trend in TX95p and TX99p, but vast majority of the mainland China showed a decreasing trend in TN5p and TN01p; and (3) the trends of TX95p and TX99p mutations time were in about 1990s or 2000s, but the trends of TN05p and TN01p has mutated in the late 1970s and early 1980s. After the mutation, the increasing trend of warm day and hot day is greater than before in most regions which indicated that more potential risk of heatwaves in future, but the decreasing trend of cold day and frozen day is not enlarge than before.

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