Effects of Climate Changes on Net Ecosystem Exchange of CO2 and Evapotranspiration of a Tropical Rain Forest

Abstract

The possible changes of Net Ecosystem Exchange (NEE) of CO2 and evapotranspiration (E) of a tropical rain forest due to climate change are described using a process-based CO2/H2O exchange model (Mixfor-SVAT). Projections of future climate conditions are provided by a global ECHAM5 model for the Special Report on Emission Scenarios (SRES) A1B. As a key region for this study, the tropical rain forest situated in Lore-Lindu National park in Central Sulawesi in Indonesia was selected. Results of the modeling experiments showed a very high sensitivity of NEE and E of this tropical rain forest to both the projected climate changes and the possible reduction of nutrients in plants due to the impact of gradually elevated CO2 in the air and depletion of soil nutrient resources. Under optimal conditions for carbon assimilation and biomass production, i.e. when the CO2 increase in the air is strictly balanced with nutrient supply, the projected climate changes will lead to increase of Gross Primary Production (GPP) by 21.3%, insignificant change of annual NEE and decrease of E by 18%. The ratio of E and precipitation, which determines the surface moisture conditions, decreases by 29.9% (from 0.78 to 0.55). It can lead to increases of soil wetness, ground water level and surface runoff in the study area in future. Limited nutrient supply can significantly reduce GPP, NEE and E. In particular the decrease of nutrient supply of about 20% can completely offset the possible GPP increase due to projected increases of temperature and CO2 concentration in the air.