The change of sunshine duration in Guide County, Qinghai Province in recent 50 years.

The annual,seasonal and monthly variation of sunshine duration and its relationship with cloudiness and precipitation in recent 50 years were analyzed in Guide County,and sunshine duration was detected and analyzed under Mann-Kendall climate sudden change theory.The results showed that annual sunshine duration generally had a decreasing tendency over the last 50 years with large annual variation range,and there was a difference of 357.5 h between peak point(1963) and valley point(1975).Sunshine duration changed obviously with seasons,and the sequence of seasonal sunshine duration was summer winter spring autumn.Sunshine duration had a slight increase in April,May and November and a decrease in other months.The sunshine duration change was in good agreement with total cloudiness from February to July,while the sunshine duration changes in autumn and winter had an opposite tendency with total cloudiness.Meanwhile,there was a significant negative correlation between annual precipitation and sunshine duration,the valley of annual precipitation and the peak of sunshine duration occurred in the same year.