Abstract ID: 412

Overview of surface water and heat fluxes across savanna - forest biome gradient in Brasil

We discuss the seasonal pattern of water vapour and sensible heat surface fluxes, across a savanna - forest biome gradient, using a flux tower network in Brasil during the LBA experiment. Distinct ecosystems were compared, namely the tropical humid and semi-deciduous forests, transitional forest, floodplain (with physionomies of Cerrado), and Cerrado sensu stricto. We suggest that the seasonality of evaporation and sensible heat flux identify two distinct types of sites that show characteristics of either a tropical forest or savanna. The mean annual sensible heat flux at all sites varied from 20 to 38 Wm-2 and was generally lower in the wet season and higher in the late dry season, consistent with seasonal variations of net radiation and soil moisture. At the sites where the dry season length does not exceed 4 months and annual precipitation is above 1900 mm, the monthly net radiation progressively increased along the the dry season and was positively correlated with evaporation, that increased to as much as 4 mm d-1, as in Manaus (central Amazonia), Santarem (eastern Amazonia) and with similarity in Rondonia (southern Amazonia). In contrast, those ecosystems with less precipitation, below 1700 mm, and longer dry season, as in Mato Grosso, Tocantins and Sao Paulo, showed clear evidence of reduced evaporation in the dry season, to 2,5 mm d-1 in the transitional forests and to 1 mm d-1 in the Cerrado. As well, the monthly evaporation and net radiation in the transitional forest and floodplain were inversely proportional during the last half of the dry season.The later sites showed characteristics of savanna, where the reduction of evaporation is more pronounced associated with longer dry season lengths and larger annual amplitude of air temperature. The patterns of seasonal evaporation and energy partitioning we have discussed is key to identifying two functionally different type of sites, that help to to explain the complexity of functioning of tropical forests, savannas, and the transitional ecosystems that exist in between them

Session:  Carbon - The role of seasonality in carbon and water balance.

Presentation Type:  Oral