Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration

Abstract

; Schmid, H. P.; Stoy, P. C.; Suyker, Andrew E.; and Verma, Shashi, "Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration" (2010 Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration AbstractVegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site-years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two-stream albedo submodel provided accurate predictions of boreal needle-leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two-stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo 5 0.01 1 0.071%N, r 2 5 0.91; forests, grassland, and maize: albedo 5 0.02 1 0.067%N, r 2 5 0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two-stream albedo model and foliage nitrogen concentration. These nitrogen-based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.

Quantifying energy and water fluxes in dry dune ecosystems of the Netherlands

“…The dense moss mat Campylopus introflexes entirely covers the underlying mineral soil, which results in a low albedo (0.135) due to the dark green surface. The albedo of bare sand (0.261) is comparable to values found in literature for bare dry coarse soils (Qiu et al, 1998;Van Bavel and Hillel, 1976;Linacre, 1969;Liakatas et al, 1986) and the albedo for grass (0.179) is consistent with values reported in other studies during summer time (Hollinger et al, 2010) or for dried grass (Van Wijk and Scholte Ubing, 1963). Heather has a somewhat lower albedo (0.078) than was found in the literature: Miranda et al (1984) report an albedo of 0.13 (Calluna, LAI ca.…”

Impact of revised and potential future albedo estimates on CCSM3 simulations of growing‐season surface temperature fields for North America

“…The CCSM3 is a coupled climate model for simulating the earth's past, present, and future climate states (Collins et al, 2006) Impact of revised albedo estimates on CCSM3 temperature simulations 321 leaf and stem reflectance and transmittance parameters that are combined to generate scattering coefficients used to calculate surface albedo values via the Sellers (1985) two-stream radiative transfer scheme (Hollinger et al, 2010). The CCSM3 default values for these parameters are identical to the leaf and stem reflectance and transmittance values published in Dorman and Sellers (1989) (Table I).…”

“…Recent results (Ollinger et al, 2008;Hollinger et al, 2010) have also demonstrated a correlation between foliage nitrogen and canopy albedo. In a world where the nitrogen cycle continues to be widely perturbed (Vitousek et al, 1997), one potential result of anthropogenic nitrogen deposition could be increases in vegetation albedo.…”

“…Because grassland and needle-leaf tree vegetation are regionally important land-cover types, errors in albedo for these PFTs may result in regional errors in predicted climate characteristics. The first objective of this study is to explore the consequences of updated grassland, needle-leaf, and deciduous tree/shrub albedo estimates (based on the albedo measurements of Hollinger et al (2010)) on Community Climate System Model -Version 3 (CCSM3) (Collins et al, 2006) 'current climate ' (1990-1999) simulations of growing-season surface temperatures over North America.…”

“…The LSMs of many climate models [e.g., community land model (CLM); Oleson et al, 2004] utilize the same (or slightly modified) two-stream model of canopy radiation transport described by Sellers (1985) to calculate albedo on the basis of foliage optical characteristics, leaf area index, and plant stem area index (Dorman and Sellers, 1989). Hollinger et al (2010) recently compared towerbased measurements of growing-season albedo from sites in the AmeriFlux network with estimates from the two-stream canopy radiation transport model as implemented in the CLM (Oleson et al, 2004). They found good agreement between measured and modeled albedos for several plant functional types (PFTs) including broadleaf deciduous trees, needleleaf evergreen trees, and various crop species, but large and systematic biases for grassland and needleleaf deciduous trees (NDTs).…”