Abstract
While previous studies largely focus on extreme events, little is known about the behaviors of mild weather, a positive and pleasant condition occurring frequently, directly associated with outdoor activities, and highly relatable to the public. Here we examine the climatological characteristics and long-term trends of mild weather over China during 1971–2014, as well as the possible linkage with the El Niño−Southern Oscillation. It is found that, on average, China experiences 94.5 days (25.4% of all days) of mild weather in a year, and the annual number of mild days increased by 1.02% per decade (3.73 days per decade) during 1971–2014, especially in summer (1.54% per decade), spring (1.49% per decade), and autumn (1.03% per decade). We also find that most parts of China have been experiencing increasing mild weather in 1971–1998 but decreasing in 1998–2014. Clustering analysis reveals six subregions that exhibit distinct mild weather behaviors. In particular, harsh seasons (i.e., summer of southern China and winter of northern China) are becoming even less pleasant. Besides these secular trends, it is also noticed that El Niño event in the preceding winter is followed by less pleasant spring and summer and more pleasant autumn and winter in most areas of China. The results reported here have significant implications for urban planners and governmental policymakers.
Highlights
By examining the changes of mild weather conditions at more than 2,000 stations across the China over the period 1971–2014, it is found that China experiences an average frequency of 94.5 mild days in a year and summer season has the most frequent mild weather while winter bears the fewest
It is observed that the yearly frequency of mild days increases by 3.73 days decade−1 and the yearly percentage of mild weather increases by 1.02% decade−1 during 1971–2014
Heavy air pollution may interact with synoptic meteorology and affect the mild weather frequency[28,29]. It is of great significance and interest to take these factors into account when defining mild or pleasant weather as perceived by human
Summary
The mean state (i.e., multi-year climatological mean) of mild weather in China is first examined. Many parts of China (except for parts of SWC and SC) are obtaining less mild weather During the subperiod of 1971–1997 (see Figs 4f–j and 5b), increasing trends in mild weather are dominant and are observed in most seasons of all parts of China except for the spring of SC and summer of SC, SWC, and YRB. In these exceptional subregions, mild weather was becoming less frequent during 1971–1997. The decreasing tendencies are strong in southern areas such as SC, SWC, and YRB
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