More frequent cloud‐free sky and less surface solar radiation in China from 1955 to 2000

Newly available data from extended weather stations and time period reveal that much of China has experienced statistically significant decreases in total cloud cover and low cloud cover over roughly the last half of the Twentieth century. This conclusion is supported by our recent analysis of the more reliably observed frequency of cloud-free sky and overcast sky. The total cloud cover and low cloud cover have decreased 0.88% and 0.33% per decade, respectively, and cloud-free days have increased 0.60% and overcast days decreased 0.78% per decade in China from 1954-2001. Meanwhile, both solar radiation and pan evaporation have decreased in most parts of China, with solar radiation decreasing 3.1 W/m2 and pan evaporation decreasing 39 mm per decade. Combined with other evidences documented in previous studies, we conjectured that increased air pollution may have produced a fog-like haze that reflected/absorbed radiation from the sun and resulted in less solar radiation reaching the surface, despite concurrent upward trends in cloud-free skies over China.