关键词: 四季, 地理环境, Mann-Kendall检验, 小波分析, 常德市

Abstract: In order to provide more detailed reference for the utilization and planning of ecological resources in Changde city of Hunan province, the daily average temperature data from 1977 to 2011 were used to compare and analyze the variation characteristics of seasons start date and seasonal length in different geographical environments in Changde urban area and Shimen mountain area by linear tendency estimation method, Mann-Kendall method, Pearson method and Morlet wavelet analysis method. The results show that the average start date of seasons in Changde urban area and Shimen mountain area has a small difference, but it delays entering summer and autumn in Shimen county than that in Changde urban area. Compare to Changde urban area, Shimen's spring and autumn are longer, but summer is shorter, and has no difference in winter. The variation range of the start date and seasonal length of four seasons between the two areas is relatively large, especially in summer. The frequency of the difference of the start date and the seasonal length between the two areas is the highest in summer, and the difference of the start date between the two areas in spring or autumn usually only affects the length of spring or autumn, but the difference of the summer and winter season affects the adjacent two seasons. There are some differences on the period characteristics of the four seasons start dates between the two areas, the main differences on the large time scale over 20 years are in winter, and the main differences on the time scale below 20 years are in summer. The start date of summer is significantly earlier, the length of summer is significantly longer, both are sudden changes; the difference is that the length of autumn in Changde is significantly shorter, and the length of spring in Shimen is significantly shorter.

Key words: season, geographical environment, Mann-Kendall test, Morlet wavelet analysis, Changde city