Multiple observation types reduce uncertainty in Australia’s terrestrial carbon and water cycles by Vanessa Haverd , M. R. Raupach, P R Briggs, J. Canadell , P. R.Isaac, C. Pickett Heaps, S. H Roxburgh, E. van Gorsel, R. Viscarra Rossel and Z. Wang

Information about the carbon cycle potentially constrains the water cycle, and vice versa. Benefitting from the public liberation of the data necessary to drive carbon and water cycle models, a recent study by the authors of this blog post succesfully demonstrated the utility of multiple observation sets - such as provided by the TERN Auscover and OzFlux facilities - to constrain carbon and water fluxes and stores in a land surface model, and a resulting determination of the Australian terrestrial carbon budget. It exemplifies the joint use of data from observational facilities and infrastructure (e-MAST).

In observations include streamflow from 416 gauged catchments, measurements of evapotranspiration (ET) and net ecosystem production (NEP) from 12 eddy-flux sites, litterfall data, and data on carbon pools. Coupled carbon and water cycles were simulated using a modified version of the CABLE land surface scheme in the BIOS2 modelling environment, a fine spatial resolution (0.05 degrees) offline environment built on capability developed for the Australian Water Availability Project (King et al., 2009; Raupach. et al., 2009). BIOS2 includes: (1) a modification of the CABLE land surface scheme (Wang et al., 2011) coupled with CASAcnp (a biogeochemical model) and SLI (Soil-Litter-Iso, a soil hydrology model including liquid and vapour water fluxes and the effects of litter).; (2) infrastructure for the treatment of inputs (gridded vegetation cover, meteorological data and parameters) and outputs for optimum efficiency; (3) a weather generator for downscaling of meteorological data; and (4) model-data fusion capability.

Results emerging from the multiply-constrained model are as: (1) on the Australian continent, a predominantly semi-arid region, over half (0.64±0.05) of the water loss through ET occurs through soil evaporation and bypasses plants entirely; (2) mean Australian NPP is 2200±400 TgC/y, making the NPP/precipitation ratio about the same for Australia as the global land average; (3) annually cyclic (“grassy”) vegetation and persistent (“woody”) vegetation respectively account for 0.56±0.14 and 0.43±0.14 of NPP across Australia; (4) the average interannual variability of Australia’s NEP (±180 TgC/y) is larger than Australia’s total anthropogenic greenhouse gas emissions in 2011 (149 TgCeq/y).