Biogeosciences, 14, 4711-4732, 2017
https://doi.org/10.5194/bg-14-4711-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Reviews and syntheses
24 Oct 2017
Challenges and opportunities in land surface modelling of savanna ecosystems
Rhys Whitley1, Jason Beringer2, Lindsay B. Hutley3, Gabriel Abramowitz4, Martin G. De Kauwe1, Bradley Evans5, Vanessa Haverd6, Longhui Li7, Caitlin Moore8, Youngryel Ryu9, Simon Scheiter10, Stanislaus J. Schymanski11, Benjamin Smith12, Ying-Ping Wang13, Mathew Williams14, and Qiang Yu7 1Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia
2School of Agriculture and Environment, University of Western Australia, Crawley, WA 6009, Australia
3Research Institute for the Environment and Livelihoods, Charles Darwin University, Casuarina, NT 0909, Australia
4Climate Change Research Centre, University of New South Wales, Kensington, NSW 2033, Australia
5Faculty of Agriculture and Environment, University of Sydney, Eveleigh, NSW 2015, Australia
6CSIRO Ocean and Atmosphere, Canberra 2601, Australia
7School of Life Sciences, University of Technology Sydney, Ultimo, NSW 2007, Australia
8School of Earth, Atmosphere and Environment, Monash University, VIC 3800, Clayton, Australia
9Department of Landscape Architecture and Rural Systems Engineering, Seoul National University, Seoul, South Korea
10Biodiversität und Klima Forschungszentrum, Senckenberg Gesellschaft für Naturforschung, Senckenberganlage 25, 60325 Frankfurt am Main, Germany
11ETH Zurich, Department of Environmental System Science, Zurich, Switzerland
12Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden
13CSIRO Ocean and Atmosphere, Aspendale, Victoria 3195, Australia
14School of GeoSciences, University of Edinburgh, Edinburgh, UK
Abstract. The savanna complex is a highly diverse global biome that occurs within the seasonally dry tropical to sub-tropical equatorial latitudes and are structurally and functionally distinct from grasslands and forests. Savannas are open-canopy environments that encompass a broad demographic continuum, often characterised by a changing dominance between C3-tree and C4-grass vegetation, where frequent environmental disturbances such as fire modulates the balance between ephemeral and perennial life forms. Climate change is projected to result in significant changes to the savanna floristic structure, with increases to woody biomass expected through CO2 fertilisation in mesic savannas and increased tree mortality expected through increased rainfall interannual variability in xeric savannas. The complex interaction between vegetation and climate that occurs in savannas has traditionally challenged terrestrial biosphere models (TBMs), which aim to simulate the interaction between the atmosphere and the land surface to predict responses of vegetation to changing in environmental forcing. In this review, we examine whether TBMs are able to adequately represent savanna fluxes and what implications potential deficiencies may have for climate change projection scenarios that rely on these models. We start by highlighting the defining characteristic traits and behaviours of savannas, how these differ across continents and how this information is (or is not) represented in the structural framework of many TBMs. We highlight three dynamic processes that we believe directly affect the water use and productivity of the savanna system: phenology, root-water access and fire dynamics. Following this, we discuss how these processes are represented in many current-generation TBMs and whether they are suitable for simulating savanna fluxes.

Finally, we give an overview of how eddy-covariance observations in combination with other data sources can be used in model benchmarking and intercomparison frameworks to diagnose the performance of TBMs in this environment and formulate road maps for future development. Our investigation reveals that many TBMs systematically misrepresent phenology, the effects of fire and root-water access (if they are considered at all) and that these should be critical areas for future development. Furthermore, such processes must not be static (i.e. prescribed behaviour) but be capable of responding to the changing environmental conditions in order to emulate the dynamic behaviour of savannas. Without such developments, however, TBMs will have limited predictive capability in making the critical projections needed to understand how savannas will respond to future global change.


Citation: Whitley, R., Beringer, J., Hutley, L. B., Abramowitz, G., De Kauwe, M. G., Evans, B., Haverd, V., Li, L., Moore, C., Ryu, Y., Scheiter, S., Schymanski, S. J., Smith, B., Wang, Y.-P., Williams, M., and Yu, Q.: Challenges and opportunities in land surface modelling of savanna ecosystems, Biogeosciences, 14, 4711-4732, https://doi.org/10.5194/bg-14-4711-2017, 2017.
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This paper attempts to review some of the current challenges faced by the modelling community in simulating the behaviour of savanna ecosystems. We provide a particular focus on three dynamic processes (phenology, root-water access, and fire) that are characteristic of savannas, which we believe are not adequately represented in current-generation terrestrial biosphere models. We highlight reasons for these misrepresentations, possible solutions and a future direction for research in this area.
This paper attempts to review some of the current challenges faced by the modelling community in...
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