The impacts of net long-wave radiation on the surface soil thermal regimes over the Qinghai–Tibetan Plateau, China

Abstract

Radiation data measured at six stations on the Qinghai–Tibetan Plateau (QTP) were used to analyze the variation of net long-wave radiation (Ln). The stations were located in the arid, semiarid, and sub-humid climate zones, covering the major climate types of the QTP. The impacts of Ln, combined with soil temperature data, on the thermal regime of ground surfaces were evaluated. Ln varied regionally over the QTP. It decreased in the northeastern and western parts and the interior of the QTP, while it showed an increasing trend in the southeastern part of the QTP. Ln declined significantly at a rate of 0.415 MJ m−2 day−1 per decade during the past 20 years. Ln greatly influenced the freezing index (DDF). DDF and the surface freezing–thawing intensity (FTI) increased with decreasing Ln. Ln was negatively correlated with FTI and this was most pronounced with a 2-year-lag FTI. The ratio of Ln/Rs (Rs denotes the global radiation) was greater than the surface albedo (Rk/Rs) (Rk denotes the reflected radiation). Both parameters resulted in surface energy loss and a lowering of the surface temperature. The cooling effect of Ln/Rs exceeds that of Rk/Rs.