Measurement and estimation of ultraviolet radiation in Pearl River Delta, China

Global solar radiation (G) and ultraviolet radiation (UV) observed from 2005 to 2011 in Heshan (HS), China were used to investigate the temporal variability of UV radiation and its fraction to G under different sky conditions. UV and UV fraction (FUV) increased from winter to summer months with annual average daily values being 540 kJ m−2 and 4.41%, respectively. The clearness index (KT) was used to study the cloud effects on UV and FUV, a reverse relationship between KT and FUV was observed. An efficient model for estimating UV radiation in the Pearl River Delta region was then proposed and calibrated by studying the dependence of UV irradiation on KT and solar zenith angle. The model has been tested at HS and two other sites with different climatic regions in China. Long-term UV dataset from 1961 to 2012 in Pearl River Delta was then reconstructed, annual mean daily UV irradiation was about 511 kJ m-2. It reveals that there was a significantly decreasing trend for UV radiation from late 1960s to early 1990s, the decrease was the sharpest in winter months. But UV radiation in the study area also began to increase since early 1990s at the rate of 6.87 kJ m−2 y−1.