Analysis of Temporal and Spatial Characteristics of Sunshine Duration Change in Hexi Arid Region: A Case Study of Heihe River Valley in the Middle Region of Hexi Corridor

This paper analyzes the temporal and spatial characteristics of sunshine duration change in recent 50 years in Heihe River Valley, which is located in the Middle of Hexi Corridor. Morlet wavelet analysis and non-parametric statistical methods, such as Mann-kendall and Geostatistic software ArcGIS (9.X) are employed. The results show that in the study area, the annual average sunshine duration increases at an average rate of 18.77h/a in recent 50 years, but this tendency is not significant. In addition, the tendency is different from most other areas in China. The increasing tendency occurs throughout the four seasons with rates of 7.13h/a, 7.72h/a, 3.18h/a and 6.96h/a from spring to winter. Annual and seasonal changing trends of sunshine duration in Heihe River Valley exhibited spatial variation. In term of annual mean sunshine duration, Jiuquan, Jinta and Dingxin were the boundary of sunshine duration change. There was an increasing tendency in the north of Hexi corridor, and the changing range of sunshine duration was above 8.0h/a, while sunshine duration in the south decreased by about 1.9~31.5h/a. Moreover, annual sunshine duration change in Heihe River Valley also exhibited temporal variation. Put ascensive central Jinta was regarded as the center for increase in sunshine duration, while Gaotai was described as the center for decrease. Jinta exhibited increasing tendency in 1960s, but from the beginning of 1970s to the middle of 1980s, sunshine duration in Jinta displayed a downtrend. After that, it demonstrated an increasing tendency again. In 1960s, there was a slight increasing tendency in Gaotai, but at the beginning of the 1970s, sunshine duration decrease noticeably. From the beginning of 1980s to the middle of 1990s, sunshine duration in Gaotai showed an obvious increasing tendency. After the middle of 1990s, sunshine duration in Gaotai kept decreasing. Sunshine duration change in Heihe River Valley fluctuated with a cycle of 12 years and a subordinate cycle of 5 years, and it exhibited inter-decadal oscillation. There was a sudden change in sunshine duration in 1975, after which the increasing trend turned to a decreasing tendency. The significant changes can mean that cloudage led to the variation in annual and seasonal change of sunshine duration in the study area. The causation of sunshine duration change in spring and autumn is not covered in this paper and needs further study.