Abstract
Land-atmosphere interactions are an important component of the climate system.
This thesis examines the role of soil moisture variability on the surface climate
of Australia including the role of vegetation on these interactions. First, the sensitivity
of the Weather and Research Forecasting Model to land surface initialisation is
examined. Simulation skill increases if soil moisture and soil temperature is suitably
initialised using values obtained from offline simulations. Secondly, land-atmosphere
coupling is evaluated for Australia using four atmospheric physics configurations and
two soil moisture scenarios. Australia is demonstrated to be a coupling "hotspot",
similar to those previously identified in the Northern Hemisphere. Thirdly, the impact
of land use change on land-atmosphere coupling is examined. Regions where
vegetation changes from forest to crops are associated with a weakening of the
coupling, independent of which model physics are used. This was associated with
changes in the surface energy balance that accompany land use change. Finally the
resistances to moisture transfer from the land surface to the atmosphere are examined
for their influence on land-atmosphere coupling. Perturbations to the aerodynamic
resistance change the partitioning of the surface turbulent energy fluxes and
subsequently surface temperature. This was associated with the aerodynamic resistance
perturbing the terrestrial and atmospheric components of the coupling. The
results suggest that land-atmosphere coupling acts mostly through the aerodynamic
resistance from the soil surface to the displacement height, which is a function of
the boundary layer friction velocity, vegetation cover and vegetation height. Overall
this research suggests that the role of vegetation on land-atmosphere coupling is
driven by the aerodynamic characteristics of the land surface, which are determined
by the parameterisation of the boundary layer and description of the land surface.