Characteristics of the water and energy balance in an Amazonian lowland rainforest in Venezuela and the impact of the ENSO-cycle

SummaryFrom 1996 to 2000 microclimatic conditions (profiles of wind-speed, temperature, humidity and radiation) have been investigated to determine the energy balance within a primary Amazonian rainforest in southern Venezuela (Surumoni crane project), located on the banks of the upper Rio Orinoco. Since 1997 main components of the water balance were examined additionally: gross and net precipitation, stemflow, sapflow and soilwater were measured. The main goal was to determine the water and energy balance for the study site as a contribution to an interdisciplinary ecological research project and to assess consequences of possible land use change. In this study the most important link between energy balance and hydrological cycle, the evapotranspiration, was determined independently by two different approaches.The results indicate a high interannual variability, which probably was influenced by the strong La Niña-epsiode in 1996 and the very strong El-Niño-event in 97/98. The impact of the ENSO-cycle is well documented for coastal and marine environments in South America; detailed observations in the Amazon basin however, are very scarce. Beyond the scope of supplying detailed information for a typical pristine tropical lowland forest, this study may also help to improve the understanding of ecosystem impact of ENSO in the Amazon region.