How energy and water availability constrain vegetation water-use along the North Australian Tropical Transect

Document Type: Research Paper

Authors

1 Key Laboratory of Water Cycle & Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy ofScience, Beijing 100101, China.

2 Water for a Healthy Country Flagship, CSIRO Land and Water, Canberra, ACT, Australia.

3 Department of Biology, Macquarie University, NSW 2109, Australia.

4 School of Life Sciences, University of Technology Sydney, P.O. Box 123, Broadway, NSW, 2007, Australia.

5 School of Earth and Environment, The University of Western Australia, Crawley, WA, 6009, Australia.

6 CSIRO Ocean and Atmosphere Flagship, Private Bag 1, Aspendale, Victoria 3195, Australia.

7 National Meteorological Center, Beijing 100081, China

8 eSchool of Life Sciences, University of Technology Sydney, P.O. Box 123, Broadway, NSW, 2007, Australia

9 Key Laboratory of Water Cycle & Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy ofScience, Beijing 100101, China

Abstract

Energy and water availability were identified as the first order controls of evapotranspiration
(ET) in ecohyrodrology. With a ~1,000 km precipitation gradient and distinct wet-dry climate,
the North Australian Tropical Transect (NATT) was well suited for evaluating how energy and
water availabilities constrain water use by vegetation, but has not been done yet. In this study,
we addressed this question using Budyko framework that quantifies the evapotranspiration as a
function of energy-limited rate and precipitation. Path analysis was adopted to evaluate the
dependencies of water and carbon fluxes on ecohydrological variables. Results showed that the
major drivers of water and carbon fluxes varied between wet and dry savannas: down-welling
solar radiation was the primary driver of the wet season ET in mesic savanna ecosystems, while
soil water availability was the primary driver in inland dryland ecosystems. Vegetation can
significantly regulate water and carbon fluxes of savanna ecosystems, as supported by the
strong link of LAI with ET and GPP from path analysis. Vegetation structure (i.e. the tree:grass
ratio) at each site can regulate the impact of climatic constraint on ET and GPP. Sites with a low
tree:grass ratio had ET and GPP that exceeded sites with high a tree:grass ratio when the grassy
understory was active. Identifying the relative importance of these climate drivers and
vegetation structure on seasonal patterns of water use by these ecosystems will help us decide
our priorities when improving the estimates of ET and GPP.


Keywords