Radiation partitioning and its relation to environmental factors above a meadow ecosystem on the Qinghai-Tibetan Plateau

Understanding the energy balance on the Qinghai-Tibetan Plateau is essential for better prediction of global climate change. To characterize the energy balance on the plateau, we examined the radiation partitioning over a Kobresia meadow, the most widely distributed vegetation on the plateau, for the period from 2002 to 2005. The incident solar radiation (R-s) and net radiation (R-n) averaged 6298 and 2779 MJ m(-2) yr(-1), respectively. The albedo averaged 0.220 annually, with a slightly low value of 0.202 in the growing season from May to September. An increase in soil water or leaf area index was correlated with a decrease of albedo over the meadow. The annual solar radiation lost 34% as longwave radiation, which was higher than values reported for lowland grasslands. The annual radiation efficiency (R-n/R-s) over the meadow, at an average of 0.44, was, however, much lower than that for lowland grasslands. The net longwave radiation (L-n) and the normalized effective radiation (L-n/R-s) over the meadow were much higher than that for the global surface or for lowland grasslands, indicating that the longwave exchange between alpine meadow and atmosphere is the most important component of energy losses. A path analysis suggests that the water vapor pressure, air temperature, and cloud cover are the major factors governing the variations of both the net radiation and the net longwave radiation in the alpine meadow ecosystem.