Spatiotemporal variations in land surface albedo across Canada from MODIS observations

A detailed knowledge of spatiotemporal variations in surface albedo is crucial if surface-atmosphere energy exchanges are to be accurately represented in climate models. Satellite observations can provide this information. This study uses moderate resolution imaging spectroradiometer (MODIS) data to investigate how summer and winter albedos, and the intra-annual variation in albedo, vary across the Canadian landscape. We show that (i) albedos generally decrease as one moves from grassland to broadleaved forest to needleleaved and mixed forest; (ii) the effects of snow on albedo vary among cover types; (iii) the largest intra-annual albedo variations occur over grasslands, cropland, and tundra; (iv) significant differences in albedo occur not only among broadleaved forest, needleleaf forest, grassland, and tundra, but also among their various canopy types (e.g., open versus closed canopies); and (v) land cover types sharing similar albedos in winter do not necessarily share similar albedos in summer. These trends are caused by differences in canopy structure and are supported to varying degrees by other in situ and remote sensing studies. These results suggest that the use of overly general land cover classes (e.g., needleleaved forest, grassland, tundra) in climate models will ignore important local-scale spatial variations in surface albedo.