New Journal of Geophysical Research Paper on Biomass Heat and Biochemical Energy Associated With Vegetation Processes – Two Important Largely Neglected Climate Processes

An important new paper is in press in the Journal of Geophysical Research entitled “Influences of biomass heat and biochemical energy storages on the land surface fluxes and radiative temperature” [the paper is not yet available online]. The authors are Lianhong Gu, Tilden Meyers, Stephen G. Pallardy, Paul J. Hanson, Bai Yang, Mark Heuer, Kevin P. Hosman, Qing Liu, Jeffery S. Riggs, Dan Sluss, and Stan D. Wullschleger.

This very original paper identifies two generally ignored climate processes which have significant effects on daily, seasonal and longer term temperature variations and trends. The abstract reads,

“The interest of this study was to develop an initial assessment on the potential importance of biomass heat and biochemical energy storages for land – atmosphere interactions, an issue that has been largely neglected so far. We conducted flux tower observations and model simulations at a temperate deciduous forest site in central Missouri in the summer of 2004. The model used was the comprehensive terrestrial ecosystem Fluxes And Pools Integrated Simulator (FAPIS). We first examined FAPIS performance by testing its predictions with and without the representation of biomass energy storages against measurements of surface energy and CO2 fluxes. We then evaluated the magnitudes and temporal patterns of the biomass energy storages calculated by FAPIS. Finally, the effects of biomass energy storages on land – atmosphere exchanges of sensible and latent heat fluxes and variations of land surface radiative temperature were investigated by contrasting FAPIS simulations with and without these storage terms. We found that with the representation of the two biomass energy storage terms, FAPIS predictions agreed with flux tower measurements fairly well; without the representation, however, FAPIS performance deteriorated for all predicted surface energy flux terms although the effect on the predicted CO2 flux was minimal. In addition, we found that the biomass heat storage and biochemical energy storage had clear diurnal patterns with typical ranges from -50 to 50 and -3 to 20 Wm-2, respectively; these typical ranges were exceeded substantially when there were sudden changes in atmospheric conditions. Furthermore, FAPIS simulations without the energy storages produced larger sensible and latent heat fluxes during the day but smaller fluxes (more negative values) at night as compared with simulations with the energy storages. Similarly, without-storage simulations had higher surface radiative temperature during the day but lower radiative temperature at night, indicating that the biomass energy storages act to dampen the diurnal temperature range. From these simulation results, we concluded that biomass heat and biochemical energy storages are an integral and substantial part of the surface energy budget and play a role in modulating land surface temperatures and must be considered in studies of land atmosphere interactions and climate modeling.”

Excerpts from the conclusions read,

“Biomass heat and biochemical energy storages are an integral and substantial part of the surface energy budget at this Missouri Ozark forest site…….. Averaged over the simulation period (four summer months) in our study, the biochemical energy storage is about 4.1±0.1 Wm-2…….. For comparison, the radiative forcing of greenhouse gases (CO2, CH4, N2O, and halocarbons together) is about 2.43 Wm-2 above the pre-industrial level [IPCC, 2001]; this value could be smaller in the current atmosphere since some of the earlier imbalance presumably has already warmed the climate system. Thus at least at regional scales, biochemical energy storage is on the same order of magnitude as the radiative forcing of atmospheric greenhouse gases. Therefore, for long-term climate system modeling which includes vegetation processes, biochemical energy storage could be important, particularly at regional scales……Biomass heat and biochemical energy storages act to reduce daytime surface temperature and increase nighttime temperature, thus leading to decreased DTR [Diurnal Temperature Range]…….We emphasize that our estimate of influences of biomass heat and biochemical energy storages on DTR (0.5 C) is conservative because we did not consider the feedback from changes in biomass temperature on the atmospheric forcing temperature. If this feedback is considered, the effect of biomass heat and biochemical energy storages on DTR might be even larger……

Finally, biomass distribution is spatially heterogeneous, which means that biomass heat and biochemical energy storages must be also spatially heterogeneous. This heterogeneity is in essence a form of gradient radiative forcing [Matsui and Pielke, 2006]. In conjunction with spatial variations in evapotranspiration, albedo, and surface roughness associated with vegetation cover, it can influence horizontal pressure gradients and mesoscale atmospheric circulations and therefore regional climates. More studies are needed in this area.”

Climate Science will alert readers when the paper becomes available online.

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