Improving surface fluxes from space: tuning two-stream vegetation properties with MODIS

James Lende¹, Leong-Wai Siu¹, Michael Brunke¹, Xubin Zeng¹

Department of Hydrology and Atmospheric Sciences, University of Arizona

Poster Session Abstract

Surface albedo, the ratio of reflected light off Earth’s surface, is a key parameter for the surface radiation and energy cycle with impacts on photosynthesis, temperature, and weather. Climate models such as the Community Earth System Model version 2 (CESM2) and the Energy Exascale Earth System Model (E3SMv) use the two-stream approximation of Dickinson (1983) and Sellers (1985) to compute surface albedo of different vegetation types. Recent model intercomparison reports have shown deficiencies in land surface albedo and surface energy fluxes, raising questions about how to improve albedo over vegetated and non-vegetated surfaces. When comparing model output albedo to MOderate Resolution Imaging Spectroradiometer (MODIS) albedo, we see consistent albedo differences in regions dominated by the same vegetation type. Over non-vegetated land, we see consistent differences in regions of the same soil color. In this study, we address deficiencies in climate model land surface albedo by utilizing an offline two-stream approximation model to tune vegetation optical properties for each plant functional type to better represent MODIS albedo. We also fit soil reflectance values to improve albedo over desert regions. Our results show reductions in bias of surface albedo compared to MODIS as well as impacts on surface fluxes such as latent and sensible heat and carbon production.