Effects of vegetation heterogeneity and surface topography on spatial scaling of net primary productivity

[摘要] Due to the heterogeneous nature of the land surface, spatial scaling is aninevitable issue in the development of land models coupled withlow-resolution Earth system models (ESMs) for predicting land-atmosphereinteractions and carbon-climate feedbacks. In this study, a simple spatialscaling algorithm is developed to correct errors in net primary productivity(NPP) estimates made at a coarse spatial resolution based on sub-pixelinformation of vegetation heterogeneity and surface topography. Aneco-hydrological model BEPS-TerrainLab, which considers both vegetation andtopographical effects on the vertical and lateral water flows and the carboncycle, is used to simulate NPP at 30 m and 1 km resolutions for a 5700 km² watershed with an elevation range from 518 m to 3767 m in theQinling Mountain, Shanxi Province, China. Assuming that the NPP simulated at30 m resolution represents the reality and that at 1 km resolution issubject to errors due to sub-pixel heterogeneity, a spatial scaling index(SSI) is developed to correct the coarse resolution NPP values pixel bypixel. The agreement between the NPP values at these two resolutions isimproved considerably from R² = 0.782 to R² = 0.884 after thecorrection. The mean bias error (MBE) in NPP modelled at the 1 km resolutionis reduced from 14.8 g C m⁻² yr⁻¹ to 4.8 g C m⁻² yr⁻¹ incomparison with NPP modelled at 30 m resolution, where the mean NPP is 668 g C m⁻² yr⁻¹.The range of spatial variations of NPP at 30 mresolution is larger than that at 1 km resolution. Land cover fraction isthe most important vegetation factor to be considered in NPP spatialscaling, and slope is the most important topographical factor for NPPspatial scaling especially in mountainous areas, because of its influence onthe lateral water redistribution, affecting water table, soil moisture andplant growth. Other factors including leaf area index (LAI) and elevationhave small and additive effects on improving the spatial scaling betweenthese two resolutions.

[学科分类] 地球化学与岩石