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Climatology - Research - GES

Patterns and processes of carbon and water budgets northern Australian landscapes: From point to region

Investigators

Summary

Carbon and water are cycled through the atmosphere, biosphere, geosphere and oceans and strongly influence climate, food supply, and the quality of the environment. International policy is concerned with managing the carbon cycle to stabilise greenhouse gases and to avoid dangerous interference with the earth system. This project will advance our understanding of patterns and processes of these cycles within the 'Top-end' of Australia, which is an underrepresented area and one that has potential for carbon sequestration through land management. We will develop tools for determining carbon and water budgets at high spatial resolution using a combination of observations linked together by a coupled mesoscale/biogeochemical model.

The project is funded from 2007 to 2009.

The full project proposal can be found here (PDF ).

Trace gas measurement at Fogg Dam (Jenny Randle)

Project Overview

Understanding the nature of the carbon cycle, including the natural and modified patterns of sources and sinks on land and in the oceans, is an essential prerequisite for tackling climate change at its most fundamental level - management of the carbon cycle at the local to regional levels (AGO 2005). Carbon is naturally transferred between atmospheric, oceanic and terrestrial pools via a rich array of chemical, physical, biological and - more recently - human processes (in its entirety this approach is known as Earth System Science). Determining the spatial and temporal patterns of these fluxes gives invaluable insights into the processes that drive the carbon cycle, and contributes strongly to the knowledge base required to manage the carbon cycle responsibly. Although there are currently several methodologies used (inventory, carbon accounting, flux towers, aircraft, model inversions) or proposed for constructing carbon budgets, they currently do not agree well. Therefore systematic regional, national and global observations must be undertaken in order to underpin our understanding of ecosystems and climate/earth systems (IPCC 2001). Currently our understanding and modelling of these systems is limited by observations of patterns and processes. It must be noted that no single methodology is capable of providing robust estimates across regions and continents through time. A synergy of approaches is needed to elucidate the patterns and processes.

Patterns and processes of the Australian carbon cycle are likely to be unique because of Australia's nutrient poor soils, water limitations, high climate variability and distinctive/diverse vegetation and fauna (Braithwaite 1990). Within this framework, we propose a three year project to advance our understanding of the regional patterns and processes of carbon, water and energy cycles within the 'Top End' of Australia (top third of the Northern Territory). We aim at developing policy relevant tools for spatially explicit carbon and water budgets using a combination of tower-based fluxes ("temporally continuous, but at single locations only") and aircraft-based fluxes budget measurements ("spatially resolved, but temporally intermittent"), combined with satellite remotely sensed quantities ("temporally and spatially continuous, but not measuring the relevant quantities directly") and linked together through a coupled mesoscale/biogeochemical model. The Top End has been chosen in this particular study for several reasons (outlined below); however, the tools developed here can be applied at other Australian 'hot-spots' and the data and process based understanding will be used to develop models that can be applied across the Australian landscape.
We seek more broadly in this proposal to address the following research questions:

1. What is the spatial variability of carbon, water and energy cycles across important ecosystem types in the Top End region during the wet and dry season and what are the key differences in ecosystem characteristics and function that drive this variability?
2. Can the fluxes of carbon, water vapour and heat over the various ecosystems as derived from the various measurement techniques be combined to form a comprehensive and consistent estimate of the fluxes and budgets over the Top End landscape?
3. Can a coupled mesoscale/carbon model together with the process understanding as derived in Questions 1 and 2 replicate and predict the spatial budgets?
4. How do our observed and modelled values compare to the Australian National Carbon Accounting System (NCAS) and other estimates?

Background

This study aims to quantify, for the first time, the spatial variability of the cycles of carbon, water and energy across the Top End landscapes from a 'bottom-up' approach. Such a large, integrated and regional approach has not been attempted before in Australia. It is only now that we have the longer-term measurements from single sites using flux towers (Beringer, Hutley et al. 2005), the technology to measure fluxes reliably using aircraft (Isaac, Leuning et al. 2004; Isaac 2005) and the knowledge to model biogeochemical cycles (Pyles, Weare et al. 2003) that we can address this problem in an integrated way. Our measurements will be able to define regional scale carbon budgets that can be used to assess the sink/source strength of Australia's northern regions and hence their contributions to the national carbon inventory (AGO 2001).

We will quantify the carbon budget of the Top-End and identify the contribution of different vegetation types to the National Carbon Inventory, a task that is identified as extremely important by the National Land and Water Resources Audit (NLWRA 2000). The key to this is the linked carbon and water cycles between the Australian land surface and the atmosphere. This exchange plays a key role in the terrestrial biospheric components of Australia's greenhouse gas inventory and in the landscape budgets of carbon and water that are crucial measures of land use viability.

From a policy perspective, Australia's large land mass coupled with its relatively small population means that terrestrial sources and sinks play a disproportionately large role in the continental carbon balance compared to most other industrialised countries. Knowledge of the patterns of natural and modified carbon fluxes across the continent is essential to support Australia's policy development and international negotiating position on climate change issues (AGO 2005).

International agreements (IPCC, UNFCC, Kyoto) require reporting of greenhouse gas emissions and carbon inventories. The IPCC reporting process likely to move from a focus on anthropogenically-driven carbon fluxes towards 'full carbon' budgets that will require countries to provide information on spatial and temporal patterns of terrestrial CO2 fluxes at high resolution, both spatially and temporally (FAO 2002). For Australia, a complete understanding of the patterns and processes of biogeochemical cycling will be required and constructing full carbon budgets proposed here will make a major contribution to a more fundamental understanding of the behaviour of the carbon cycle.

Australia is already moving towards a full carbon accounting system using the National Carbon Accounting System (NCAS)(AGO 2002). NCAS represents a major achievement for Australia in terms of accounting and is based on a sophisticated compilation of huge datasets and is coupled with satellite data to give monthly carbon accounts at high resolution. However, NCAS is designed as an accounting tool and reporting instrument and is not a full biogeochemical model nor is it a coupled climate/carbon model. Therefore, it does not yet represent a tool for simulating full carbon budgets across regions or the continent. Our challenge remains to describe and understand land-based carbon patterns and processes well enough to construct an internally consistent and robust regional carbon budget through time. This project will complement the existing NCAS by providing new information on processes and spatial variability of carbon and water budgets and also allow a unique and comparative measure of regional carbon budgets.

Approach

The aims of this project will be accomplished through systematic ecophysiological, flux tower observations, intensive aircraft campaigns and modelling of carbon sources and sinks, along with utilisation and synthesis of existing data sets. These activities support each other through an integrated strategy to answer our research questions (E2). This strategy is based on the premise that spatial and temporal patterns and processes of carbon sources and sinks, and the need to develop useful predictive tools can not be addressed by one measurement or modelling strategy alone. However a "synthesis of techniques promises efficient, long term, globally consistent quantification and monitoring of sources and sinks at regional and continental scales" (Raupach in (GTOS 2000) p. 88).

It is convenient to describe the observational and modelling Work Programs (WP) separately below (Fig 1); however, each activity will inform the other. A general theme is also to integrate across scales from the plot based tower measurements (WP1) to regional budgets using aircraft (WP2) and coupled mesoscale/carbon models (WP3) (Fig 1). The strategy is such that the observations will test related aspects of the models as thoroughly as possible. This involves ensuring that the models predict relevant observable quantities, and that observations are made of the model parameters that are most sensitive. We will develop techniques to provide spatially explicit carbon and water budgets for regions using multiple tools to constrain our flux estimates.

WP 1 - Ecosystem plot scale patterns and processes
At the ecosystem plot scale (~1 km) we will measure hourly fluxes of carbon, water and energy simultaneously above 5 surfaces including 4 key terrestrial ecosystem types using the tower based eddy covariance (EC) technique (Baldocchi and Meyers 1998). We are focused on the spatial variability rather than temporal (interannual variability) and therefore we will make measurements for these vegetated sites over a period of 24 months, from mid-year 1 to mid-year 3, in order to capture at least the important seasonal dynamics of the monsoonal tropics. Four of the five towers will be provided from existing equipment or borrowed (one new system is requested) and all will be installed during the first dry season. The long-term site at Howard Springs (open forest savanna) will provide insight into the long-term temporal changes in the Top End .
WP 2 - Regional fluxes and spatial variability using aircraft measurements
Using the unique facilities available at Airborne Research Australia (ARA) (Hacker), we propose to use two aircraft to simultaneously apply methods which will cross-verify each other. This is a novel approach that has to our best knowledge not been implemented anywhere before. Limited wet season measurements have been made and we will concentrate the aircraft measurements in the dry season.
WP 3 - Scaling up from point to region using a coupled mesoscale and landsurface/biogeochemical model
In order to determine the spatial variability and regional budgets we need to scale up the patch scale information from the towers (WP 1). The towers will measure over key ecosystem types and each type will be simulated by a higher-order turbulence closure model with full biogeochemistry and sophisticated vegetation scheme (ACASA) (Pyles, Weare et al. 2000).

Measurements

There will be several key sites within the Top End.

Figure: Overview of Surface energy balance sites (Google Earth)

Darwin Harbour- Inshore waters

12º 29.942’S

130º 53.194’E

Howard Springs - Eucalypt open forest savanna with woollybutt, stringybark and a sorghum tall grass understory

12º 29.655’S

131º 09.143’E

Fogg Dam - Typical northern floodplain with sedges, rushes, grasses and scattered pandanus and gebang

12º 32.552’S

131º 18.413’E

Daly River - Eucalypt woodland/grassland savanna

14º 09.557’S

131º 23.280’E

     

Data

Real time data can be found here. For longer time series and quality controlled data please contact the authors.

Climate

This is part of the coastal humid region of the Northern Territory. This region experiences two major seasons: wet and dry. The wet season generally occurs from December to March (inclusive) and during this time approximately 95% of the annual rainfall (which in this region is approximately 1750mm per annum) occurs as shown in the figure below. The dry season generally occurs from May to September (inclusive). Maximum temperatures range from 30.4ºC (in July) to 33.2ºC (in November), while minimum temperatures range from 19.3ºC (in July) to 25.4ºC (in November). Therefore, the maximum and minimum range varies from 7ºC (wet season) to 11ºC (dry season).

News and media

Photos

Outputs

Useful Links

References

AGO (2001). National Greenhouse Gas Inventory 1999. Canberra, Australia, Australian Greenhouse Office.

AGO (2002). Greenhouse Gas Emissions from Land Use Change in Australia: Results of the National Carbon Accounting System. AGO. Canberra: 32.

AGO (2005a). Blueprint for Australian Terrestrial Carbon Cycle Research. Canberra, Australian Greenhouse Office: 23.

AGO (2005b). Australian Climate Change Science Program: Stratergic research agenda 2004-2008. Canberra, Australian Greenhouse Office: 48.

Baldocchi, D., E. Falge, et al.(2001). "FLUXNET: A new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor, and energy flux densities [Review]." Bull. Am. Met. Soc. 82(11): 2415-2434.

Baldocchi, D. and T. Meyers (1998)."On using eco-physiological, micrometeorological and biogeochemical theory to evaluate carbon dioxide, water vapor and trace gas fluxes over vegetation ." Ag & For Met 90(1-2): 1-25.

Braithwaite, R. W. (1990)."Australia's unique biota: Implications for ecological processes." J. Biogeography 17: 347-354.

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Grace, J. (2004). "Understanding and managing the global carbon cycle." Journal of Ecology 92(2): 189-202.

GTOS (2000). Global Terrestrial Carbon Observation: Requirements, present status and next steps. GTOS 23. J. Cihlar, S. A. Denning and J. Gosz. Ottawa Canada.

Huntley, B. J. and B. H. Walker (1982). Ecology of Tropical Savannas. New York, Springer-Verlag.

IPCC (2001). Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. New York, NY, USA, Cambridge University Press.

Isaac, P. (2005). Estimating Surface-atmosphere Exchange at Regional Scales". Ph.D. Thesis Flinders University. Adelaide, Flinders University: 310.

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Russell-Smith, J., A. C. Edwards, et al. (2003). "Reliability of biomass burning estimates from savanna fires: Biomass burning in northern Australia during the 1999 Biomass Burning and Lightning Experiment B field campaign - art. no. 8405." JGR-Atmospheres 108(D3): 8405-8405.

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Schmitgen, S., H. Geiß, et al.(2004). "Carbon dioxide uptake of a forested region in southwest France derived from airborne CO2 and CO measurements in a quasi-Lagrangian experiment." J. Geophys. Res. 109(D14): 14302-14302.

Wang, Y. P., R. Leuning, et al.(2001). "Parameter estimation in surface exchange models using nonlinear inversion: how many parameters can we estimate and which measurements are most useful?" Global Change Biology 7(5): 495-510.

Williams, R. J., A. M. Gill, et al.(1998). "Seasonal changes in fire behaviour in a tropical Savanna in Northern Australia."Int J Wild Fire 8(4): 227-239.

Wilson, B. A., P. S. Brocklehurst, et al. (1990). Vegetation survey of the Northern Territory, Australia. Technical report No. 49. Darwin, Conservation Commission of the Northern Territory.

Acknowledgements

ARC - Australian Research Council This project is funded from 2007 to 2009 from the Australian Research Council under project number DP0772981.


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