Estimation of Terrestrial Carbon Fluxes by Integrating Remote Sensing with Ecosystem Modelling
M. K. Hazarika and Y. Yasuoka
Institute of Industrial Science, Room No. Ce-509,
University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505
Tel: (81) 3-5452-6415, Fax: (81) 3-5452-6408
E-mail: manzul@iis.u-tokyo.ac.jp
Japan
Abstract
Sim-Cycle is a carbon cycle model which retrieves carbon dynamics of various terrestrial ecosystems. This model simulates carbon fluxes on basis of bio-physical and climatic parameters. One of the most important bio-physical parameter used in the Sim-Cycle is Leaf Area Index (LAI), which is estimated using a land cover map and climatic parameters averaged over a long period of time. LAI is a highly dynamic biophysical parameter with respect to time and space and, therefore, such an approach for its estimation may not be reliable as an input parameter for a carbon cycle model. However, remote sensing data has the potential to provide prevailing condition of such parameters and their spatial extent on the ground in a repetitive manner. Therefore, LAI derived from MODIS satellite data has been integrated with the Sim-Cycle model to generate latest scenario of carbon dynamics in global scale.
Using the original Sim-CYCLE model, global annual GPP, NPP and AR are estimated as 131.2, 62.7 and 68.5 PgCyr
-1 respectively. Incorporating the MODIS-LAI in the Sim-CYCLE model, the global annual GPP, NPP and AR are re-estimated as 122.1, 59.6 and 62.5 PgCyr
-1 . Results from MODIS-LAI incorporated Sim-CYCLE shows overall lower NPP estimation than original Sim-CYCLE excepts in equatorial and northern temperate boreal forest region (50ºN-60ºN).
1. Introduction
Global climate change and its cause and effects in relation to natural as well as anthropogenic activities has been a recent focus of concern within the scientific community. The average temperature of the earth’s surface, currently at about 15º C, is controlled by the gaseous composition of the atmosphere. Relatively active or greenhouse gases in the atmosphere trap the outgoing solar radiation and keep the earth warm. Emissions and re-absorption of these gases from natural ecosystem have been in equilibrium for million of years. However, this balance has been disturbed by the human activities. Consequently, the atmospheric concentrations of the greenhouse gases, which are mostly the derivatives of carbon, have been increasing rapidly and it is widely believed that higher concentration of these gases is responsible for global warming.
The carbon balance is thus a high profile issue and it carries both scientific and political significance. The question, scientifically, is what and where are the terrestrial sources and sinks of carbon, and how they change on time scales of years to decade. The question politically is what are the annual emissions of CO
2 (and other green house gases) from each country? To answer all these questions, there is a need to understand the global carbon cycle process. Monitoring and modelling efforts have made it possible to understand the terms of global carbon balance in a broad perspective, but there are many uncertainties yet to be resolved. The largest uncertainties in the global carbon balance are associated with the net flux of carbon to and from terrestrial ecosystems (Houghton, 1995). However, use of satellite data with higher spatial and spectral resolution to determine the land cover and land-use in terrestrial ecosystems could significantly reduce such uncertainties .
