Sensitivity of Tropical Land Climate to Leaf Area Index: Role of Surface Conductance versus Albedo*

Tropical land climate sensitivities to surface properties are studied using an intermediate complexity atmosphere model. The focus here is on land surface vegetation feedbacks to the atmosphere through surface conductance and albedo. Both properties are linked by a parameterization on leaf area index so that their relative impacts can be compared. For a given percent change in leaf area index, it is found that low and moderate vegetation regions such as the Sahel have a higher sensitivity than rain forest regions such as the Amazon in local total precipitation anomaly, as well as fractional change in precipitation. Comparison of sensitivities to changes in surface conductance and albedo shows that neither is negligible and their relative influence differs among local climatic regions, typified by different vegetation types. High precipitation rain forest regions are more influenced by surface conductance due to the large water recycling ratio there, while albedo has a larger influence in arid, low vegetation regions by modifying the energy balance and large-scale atmospheric circulation. In regions of moderate precipitation and vegetation, altered surface conductance and albedo have comparable effects on precipitation. Surface conductance and albedo have opposing effects on surface temperature but surface conductance has the dominant impact on both surface temperature and evapotranspiration.