The sensitivity of climate to the loss of the Congo basin rainforest through changes in land cover properties is examined using a regional climate model. The complete removal of the Congo basin rainforest results in a dipole rainfall anomaly pattern, characterized by a decrease (∼−42%) in rainfall over the western Congo and an increase (∼10%) in the basin's eastern part. Three further experiments systematically examine the individual response to the changes in albedo, surface roughness, and evapotranspiration efficiency that accompany deforestation. The increased albedo (∼0.05) caused by the Congo basin rainforest clearance results in cooler and drier climate conditions over the entire basin. The drying is accompanied with a reduction in available surface energy. Reducing evapotranspiration efficiency or roughness length produces similar positive air temperature anomaly patterns. The decreased evapotranspiration efficiency leads to a dipole response in rainfall, similar to that resulting from a reduced surface roughness following Congo basin rainforest clearance. This precipitation anomaly pattern is strongly linked to the change in low-level water vapor transport, the influence of the Rift valley highlands, and the spatial pattern of water recycling activity. The climate responds linearly to the separate albedo, surface roughness, and evapotranspiration efficiency changes, which can be summed to produce a close approximation to the impact of the full deforestation experiment. It is suggested that the widely contrasting climate responses to deforestation in the literature could be partly due to the relative magnitude of change of the radiative and nonradiative parameterizations in their respective land surface schemes.
As part of the EXPRESSO program (EXPeriment for the REgional Sources and Sinks of Oxidants), biosphere-atmosphere exchanges of trace gases were investigated in a ground-based forest site of the Republic of Congo. Experiments were carried out in March and November-December 1996. A 60-meter walkup tower was erected in an undisturbed mixed tropical forest typical of upland vegetation in the Nouabalé-Ndoki National Park. Eight belt transects radiating from the tower were used to characterize the species composition and structure of the upland mixed forest. As a comparison, and to investigate horizontal heterogeneity of the trace gases exchanges, additional measurements were made in a nearby monospecific forest stand characteristic of lowland Gilbertiodendron dewevrei (Gilbert. dew.) forest. Micrometeorological data, trace gas concentrations and flux measurements were made from the tower. We report daily above-canopy variation in temperature and radiation, energy partitioning into latent and sensible heat flux, volatile organic compound ( VOC) mixing ratios, isoprene and CO 2 fluxes. Fluxes of isoprene and CO 2 were measured above the canopy using relaxed eddy accumulation and eddy covariance methods, respectively. These fluxes show a seasonal variation between the two experiments, as does energy partitioning. However, difference in isoprene emission between the two seasons are difficult to reconcile with meteorological (T, PAR) data only, and more data such as plant water potential are needed to modeled the seasonal isoprene emission cycle. Isoprene emission at the leaf level was also determined for plant species at both upland and lowland sites using environmentally controlled leaf enclosures. Together with the ecological survey, the leaf level work suggests that lowland Gilbert. dew. forests act as hot spots in terms of isoprene emissions. Future climate and land use changes could greatly affect the isoprene regional emission estimate through changes in the respective proportion of the upland and lowland forests, and the extent of dry versus wet season.
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