Analysis of Variation in Sunshine Duration in Sichuan Province Based on the Homogeneity Test
基于均一性检验的1961年至2006年四川省日照变化规律研究

Non-homogeneity of climate data could lead to considerable uncertainty in relevant research. In this paper, changing rules of sunshine duration in Sichuan Province were analyzed using homogeneous data. Annual sunshine data at 117 stations in Sichuan Province were collected for performing the homogeneity test using the traditional standard normal homogeneity (SNHT) method. Results showed that 54 of 117 stations have homogeneous data. Based on sunshine duration observations from the 54 stations, characteristics of changes in sunshine duration were analyzed using traditional statistical methods, e.g., linear trend, wavelet analysis, Empirical Orthogonal Function (EOF), and Mann-Kendall test. Some conclusions were drawn as follows: 1) 88.9% of the stations being used showed decreasing trends, with relatively large reduction rates occurring in the basin and the average decreasing rate of 50.94h/10a. 2) The largest decrease of seasonal sunshine duration occurred in summer, followed by winter. However, most of stations showed an increasing tendency in spring. 3) Changing trends in the inter-decadal sunshine duration were similar. From the 1960s to the 1970s, the sunshine duration increased slightly in most areas of Sichuan. In the 1980s and 1990s, it started to decline. Since the early 21st century, it exhibited a slight increase. As a whole, the sunshine duration in Sichuan from the 1960s to the 1970s showed positive anomalies, and the other periods mainly displayed negative anomalies. Meanwhile, the highest sunshine duration was found to take place in the 1970s, and the lowest one occurred in the 1990s. 4) Based on the Mann-Kendall test, t-test, and Yamamoto test, the sunshine duration showed varying mutations, with the point of discontinuity appearing in about 1980. 5) There was a marked transformation of sunshine between dimming and brightness periods. An inter-decadal variation scale of about 24 years was detected. However, it was noticed that the inter-decadal signal began weakening since the mid-1990s. The annual oscillation cycle mainly showed 6 years and 3 years, in which the 3-year cycle signal weakened in periods of the mid-1970s and the 1980s. In addition, a tendency of change over a 4-year cycle occurred since the early of 21st century.