Carbon Flux Estimation in Southeast Asia using a Eulerian-Lagrangian Coupled Inversion System and Observational Data from Multiple Platforms

Abstract:

Southeast Asia is rich in tropical forest and biodiversity. Previous inversion studies show large inter-annual variability in the biosphere-atmosphere carbon exchange attributable to climate anomalies. However, the magnitudes of estimated fluxes are significantly different among the inversions. On the other hand, land-use change has been accelerating the anthropogenic emissions. For the sustainable development in Southeast Asia under the on-going climate change, it is important to understand the biosphere-atmosphere carbon exchange and access the regional emissions. One of the reasons for the large uncertainty in flux estimate is a limited coverage of atmospheric observation against the large variety of ecosystems and the geographical complexity. Recently, the number of measurements has been increasing, including ground-based and satellite-based measurements. We estimated the regional CO₂fluxes using a Eulerian-Lagrangian inverse modeling system and examined the characteristics of observational constraints and their impacts on the flux estimate in Southeast Asia.

The results show that the temporal variations and source/sink strength of estimated regional fluxes are sensitive to the observational constraints. As a control run, we used the Observational Package (ObsPack) data product since 2001 as a global dataset of atmospheric CO₂ measurement. In the addition to Bukit, Sumatra Island (BKT) in ObsPack, we included a stationary CO₂ data at Danum Valley in Borneo Island (DMV) since late 2009. Compared to BKT, DMV shows a clear seasonal cycle. The inversion including DMV tends to increase the regional carbon sink in the second half of year. Remotely the aircraft measurements over Rarotonga (RTA) in the tropical Pacific Ocean see the signals from Southeast Asia through an atmospheric convection. The sensitivity test shows RTA impacts on the inter-annual variations of estimated flux, which might be associated with ENSO events. Since June 2009, Greenhouse gases Observing SATellite (GOSAT) has been providing the global column-averaged CO₂ fraction (XCO₂) data. Though GOSAT observations available over Southeast Asia are sparse due to the cloudy weather conditions, the large-scale spatial gradients of GOSAT XCO₂ are influential to the source/sink strengths in the region.