Effects of variability in land surface characteristics on the summer radiation budget across desert-oasis region in Northwestern China

摘要

The oasis area in the middle reaches of the Heihe River has changed since a water diversion scheme was implemented in 2000. The resultant variation land surface characteristics affects radiation budget during the oasisification process. The aim of this study was to investigate the variation in radiation budget within land surfaces during the oasisification process, through spatial instead of time-successional sequence method. Radiant data in the oasis fringe (maize field) and the desert-oasis ecotone was observed during the summer of 2009. The results showed that solar radiation (SR) in the oasis fringe was identical to that of the desert-oasis ecotone on selected clear, cloudy, and rainy days. Surface reflective radiation (SRR) and surface effective radiation (SER) both decreased from clear day to cloudy day and were lowest on the rainy day. The diurnal variation in radiation budget for cloudy and rainy days did not follow the same cycle as on clear day. The albedo values in the oasis fringe and the desert-oasis ecotone were 0.18 and 0.26, respectively. The diurnal variation in albedo tended toward a "U-shaped" curve on clear day. When the solar elevation angle was greater than 40°; the albedo was symmetrical in the a.m. and p.m. time frames. The radiation budget changed within land surfaces during the oasisification process. In summer, the albedo decreased, as did SER, with the transition from desert to oasis interior; whereas the surface-absorbed radiation (SAR) and net radiation (NR) both increased. More than half of the absorbed net energy in the desert was released in longwave form. The absorbed energy in the oasis was conserved to ensure stable light and heat resources utilization for agricultural production.