The Effects of Urbanization on Sunshine Duration and the Trend of Cloud Cover Amount Variation in Beijing Area

The authors study the seasonal and interannual variations of sunshine duration, total cloud cover amount, and low cloud cover amount in the past 48 years for both the urban and suburban areas in Beijing by utilizing the observational data from 1961 to 2008 at 12 stations in the urban and suburban areas and by employing the methods of trend analysis and accumulation bias, and also discuss the effects of urbanization on the variations of sunshine duration and cloud cover amount.For the urban area, the results have shown a decreasing trend for the total cloud cover amount, but an increasing trend for the sunshine duration. For the suburban area, the results have shown an increasing trend for the total and low cloud cover amount, but a decreasing trend for the sunshine duration. In decadal scale for these variations, the total cloud cover amount for the urban area has decreased since the beginning of the 1980s, especially in the 1990s.After 2000, the total cloud cover amount for the urban area has reversed and increased significantly, however, the low cloud cover amount for both urban and suburban areas has shown a decreasing trend with fluctuation from the 1960s to the 1980s, but an increasing trend with fluctuation from the 1990s to the 2000s. The sunshine duration for both urban and suburban areas has shown an increasing trend from the 1960s to the 1980s, but a decreasing trend from the 1990s to the 2000s. The low cloud cover amount and the sunshine duration show a negative relationship. This is closely related to the effects of urbanization on regional climate.