The Albedo of Vegetated Land Surfaces: Systems Analysisand Mathematical Modeling

Abstract

The albedo of vegetated land surfaces (surface albedo) is a key factor in climate modeling and in mechanistic accounting of many ecological processes. This paper proposes a testable numerical equation for the analysis and projection of surface albedo. Conceptualized as the manifestation of a canopy elements-determined basic property after modifications by temporal and spatial circumstances, surface albedo was depicted analytically in relation to 11 driving variables (leaf size, leaf life span, relative leaf age, canopy leaf cover, relative stem cover, vegetation height, stress-calendar day, drought indicator, optical air mass, station atmospheric pressure, snow cover). With peripheral algorithms developed to derive all but two of those variables, surface albedo was linked ultimately to eight rudimentary factors (calendar day, latitude, elevation, vegetation height, dominant plant species, monthly air temperature, monthly precipitation, snow cover). The analytical framework, and then its coefficient values, for surface albedo were generally supported by a series of statistical evaluations in terms of: (i) the equation’s ability to capture, by regression fitting, the variation in the surface albedo of 26 forests (135 data points) distributed around the world; (ii) the quantitative significance of individual driving variables; (iii) the randomness of residual or error distributions; (iv) the performance of the forests-fitted equation in extrapolative prediction of surface albedo against independent data for 8 deforested sites (93 data points) and for 3 types of vegetation (7 data points) at the Arctic treeline. Compared to the data, the fitted or projected albedo values had a margin of error generally within ±10%. The individual coefficient values and component functions of the final equation were consistent with their supposed mechanistic underpinnings, based on independent information from the literature. The equation shed new insight into the quantitative behavior of surface albedo, and upon further validation, should be useful for modeling surface albedo as a key land surface-atmosphere feedback link that varies and interacts with climate and vegetation.