New Paper On The Important Role Of Vegetation Within the Climate System

Jos de Laat of the Royal Dutch Meterological Institute (KNMI) has provided to us yet another very relevant new research paper. This article is on the role of vegetation processes within the climate center. The paper is

Effects of Land Surface-Vegetation on the Boreal Summer Surface Climate of a GCM, by Alessandri et al., Journal of Climate, 15 January 2007, doi: 10.1175/JCLI3983.1

The abstract reads

A land surface model (LSM) has been included in the ECMWF Hamburg version 4 (ECHAM4) atmospheric general circulation model (AGCM). The LSM is an early version of the Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) and it replaces the simple land surface scheme previously included in ECHAM4. The purpose of this paper is to document how a more exhaustive consideration of the land surface–vegetation processes affects the simulated boreal summer surface climate.

To investigate the impacts on the simulated climate, different sets of Atmospheric Model Intercomparison Project (AMIP)-type simulations have been performed with ECHAM4 alone and with the AGCM coupled with ORCHIDEE. Furthermore, to assess the effects of the increase in horizontal resolution the coupling of ECHAM4 with the LSM has been implemented at different horizontal resolutions.

The analysis reveals that the LSM has large effects on the simulated boreal summer surface climate of the atmospheric model. Considerable impacts are found in the surface energy balance due to changes in the surface latent heat fluxes over tropical and midlatitude areas covered with vegetation. Rainfall and atmospheric circulation are substantially affected by these changes. In particular, increased precipitation is found over evergreen and summergreen vegetated areas. Because of the socioeconomical relevance, particular attention has been devoted to the Indian summer monsoon (ISM) region. The results of this study indicate that precipitation over the Indian subcontinent is better simulated with the coupled ECHAM4–ORCHIDEE model compared to the atmospheric model alone.”

Important excerpts from the paper reads,

The coupling with ORCHIDEE has been shown to have a considerable impact on the boreal summer surface air temperature simulated by ECHAM4. A warmer 2-m temperature (T2m) is found over large continental areas in middle and high latitudes of the Northern Hemisphere. A particularly strong T2m increase is found over eastern Asia. The warmer temperature over these areas also leads to increased land– sea contrast in sea level pressure (SLP), which, in turn, induces changes in the atmospheric circulation.

“Land surface–vegetation processes have considerable biophysical effects on climate and, as evidenced in this study, their inclusion in AGCMs is a major task in order to improve our skill in surface climate simulation. In this work, a prescribed vegetation representation has been used, and the seasonal cycle of the vegetation cover is simply computed as a function of soil temperature. This kind of approach leads to an unrealistically small interannual variability in vegetation cover and, as shown in this work, a poor representation of the seasonal cycle in semiarid tropical regions. In particular, this latter shortcoming has been shown to contribute to the precipitation bias found in EchOrc over the Sahel. By virtue of these considerations, a further improvement in the simulated surface climate is expected from the inclusion in the EchOrc AGCM of a fully interactive dynamical global vegetation model, which is suitable to reproduce in a more realistic way the interannual and seasonal variations in the vegetation characteristics.”

This paper further documents the major role of vegetation on the surface air temperature (an issue which was not assessed at all in the CCSP report Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences as it should have (see), as well as the importance of vegetation processes in affecting regional climate patterns as recognized in the 2005 NRC report Radiative forcing of climate change: Expanding the concept and addressing uncertainties.

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