UVvariability in an arid region of Northwest China from measurements and reconstructions

Abstract

Ultraviolet radiation (UV) observed at Fukang (FK), China from 2004 to 2012 was used to investigate UV variability and its relationship with global solar radiation (G) under various sky conditions in Northwest China. Clearness index (Kt) was used for characterizing the sky conditions and UV model development, it was discovered that clear skies were the dominated sky conditions (48.72%), followed by partly cloudy (32.56%) and overcast (18.72%) skies. Daily FUV (fraction of UV to G) increased from November to June with an annual mean of 4.00% at FK. Meanwhile, an efficient all‐sky UV model under any sky conditions has been proposed by investigating the dependence of hourly UV irradiations on Kt and cosine of solar zenith angle μ. The model was assessed through the statistical indices: mean bias error (MBE), mean absolute bias error (MABE) and root mean square error (RMSE) whose values were 1.27 (−0.24), 4.64 (4.56) and 6.26% (6.14%), respectively at hourly (daily) basis. The model has also been tested at three other sites with distinctly different climates in China. Finally, daily UV radiation during 1961–2012 in Northwest China was reconstructed and annual mean daily UV irradiation was about 0.603 MJ m−2 d−1. UV decreased at 0.62 KJ m−2 d−1decade−1 during the whole study period and the decreases were sharpest in spring (3.28 KJ m−2 d−1decade−1), however, there was an increasing trend at the rate of 2.16 KJ m−2 d−1year−1 since 1991.

Comparison of different UV models for cloud effect study

“…The radiometric ratio of UV to G (F UV ) was computed by summing the individual fluxes (UV and G) over the course of an hour (or day), then taking the ratio F UV of the sums. The analysis in this study has been limited to cases that solar zenith angle was lower than 85 due to the differences in cosine response error and the temporal response of both radiometers [32,44]. As stated in our earlier study Wang et al [18,25,33], QC (quality control) for G was mainly based on the criterion: G should be smaller than extraterrestrial global solar radiation G 0 in the same geographical location, G/G 0 should be larger than 0.03 [48].…”

“…Table 4 showed the monthly statistics of daily a under different sky conditions. It was observed that overcast skies were the dominated sky conditions and the largest frequency was about 53.5%, followed by cloudy skies (44.4%) and clear skies ( Wuhan; a in July was 0.0489 and 0.0408 for overcast and clear days, respectively at Fukang [17,32]. These differences indicated that the effects of cloud or water vapor on UV radiation are more influential at YT and Wuhan than Fukang [54e56].…”

“…7), which was recommended to be described with power law equation [17,18,25,32,36,45,58], which can be expressed as:…”

“…It was known that K UV (UV/UV 0 ) was a good index describing the atmospheric transparency under average conditions. The ratio of UV C /UV 0 gave information about the atmospheric transparency without clouds but with aerosols [25,32,33]; the ratio of UV/UV C was also useful for studying the UV attenuation due to the influence of cloudiness. The mean decadal values of the UV attenuation indices (K UV , UV C /UV 0 and UV/UV C ) for each month of the year were shown in Fig.…”

Assessing sustainability of agricultural water saving in an arid area with shallow groundwater

“…Agricultural water‐saving practices can be effective in the light of increasing water and food demands and achieving high water use efficiency and productivity. However, increased implementation of agricultural water‐saving practices can have a negative effect on ecosystems and the environment which, in turn, are related to the water cycle (Wang et al, ; Liu et al, ). Furthermore, economic returns and improved social awareness need to be considered together when designing and planning future water‐saving practices.…”