Temporal and Spatial Change of Albedo in Beijing-Tianjin Area of China

Land surface albedo is a key parameter representing the outgoing solar flux fractions reflected by earth surface . It is widely used as an input parameter for numerical radiation budget models, the hydrological cycle and climate modeling studies. Urban’s high albedo changes the original land surface radiation balance, high thermal diffusivity insulates the ground, and thus it represents a dry, heat surface in the heat and moisture fluxes. Thus urban cover has great influences on global ecological cycle and land surface albedo. Land surface albedo is primarily altered with temporal and spatial variation. Land cover type, moisture, roughness, and solar angle are its main influence factors. Over urban surface, the temporal and spatial variation has strong relationship with human activities. In terms of the studying area (Beijin-Tianjin urban area) in this paper, during about 20 years, land cover type has converted from farmland or wasteland to urban with high radiation features, which directly increase the area of impermeable stratum on the surface. Correspondingly, other parameters such as moisture, roughness are also changed. Therefore, not only the alteration of surface albedo is reasonable, but also can the albedo results reveal exactly how some typical ground objects such as vegetation coverage, lands, large constructions etc. are modified.