Climatic Change of Sunshine Duration in the Bailong River Valley in Gannan from 1973 to 2012

Change of sunshine duration affects climate and eco-environment greatly. Using the modern statistical methods such as linear trend and abrupt change analysis, the recent 40 years(1973-2012) sunshine duration changing trend and abrupt change in the Bailong River Valley in Gannan were analyzed. The results showed that the average annual sunshine duration in the Bailong River Valley in Gannan increased significantly in recent 40 years with an increasing rate of 33.0 h/10 a. The seasonal sunshine duration showed different increasing rates,which was the largest in spring and the smallest in summer. This phenomenon was different from those occurred in most of China with a decreasing trend of sunshine duration, and reflected the unique characteristics of climate anomaly and complexity change in sunshine duration in the Bailong River Valley in Gannan. The average annual sunshine duration anomaly was negative before1994 and positive after 1994 in the Bailong River Valley in Gannan. The average annual sunshine duration as well as seasonal sunshine duration showed abrupt increase. The average annual sunshine duration presented abrupt increase in 1983, the summer sunshine duration increased abruptly in the 1990s, and increased abruptly in other seasons in the 1980s. Meanwhile, the annual sunshine duration of less anomalous years occurred in the 1980s while more anomalous years occurred only in 2002. Under background of the climate warming, the rainy days with over 0.1 mm precipitation per day decreased in the Bailong River Valley in Gannan, which was a primary cause for the increases of sunshine duration. Sunshine duration, temperature and evaporation showed a significant positive correlation and shared a strong consistency in the changing trend.