Effects of urbanization on the decrease in sunshine duration over eastern China

As an important indicator of sunlight conditions, sunshine duration (SSD) has a close relationship with human health, socio-economic activity, ecosystems, and the environment. This paper examines the long-term changes in SSD over eastern China and evaluates the possible urbanization effect on these changes based on a dynamic classification of urban and rural stations using time-varying land use/land cover maps. Daily SSD observations at nearly 2000 stations during 1961–2014 are collected and analyzed. Results show that SSD in eastern China declines throughout the year at an annual rate of −0.132 h/day per decade, with the largest trend in summer (i.e., −0.218 h/day per decade) and most moderate in spring (−0.066 h/day per decade). The dimming trend is even more profound in the highly urbanized and densely populated areas, such as the North China Plain and the Yangtze River Delta. A significant correlation of −0.48 also exists in the SSD trend and urban area fraction around the station. These results demonstrate an essential influence of local urbanization on SSD changes. It is also estimated that urbanization induces an additional decreasing trend of 0.065 h/day per decade for SSD, contributing to 35.3% of the total dimming trend in eastern China.