Williams-Climate-change-refugia-for-terrestrial-biodiversity_0

ABSTRACT
Climate change presents a challenge for the management of water resources and for
the management of systems dependent on those water resources. In particular, the
effect of water flow across and below the ground surface is rarely adequately
represented. Our motive was to capture this effect for water limited Australia, to assist
with the identification of climate change refugia. We present a new algorithm for the
rescaling of actual evapotranspiration (ETa) under future climate. The algorithm uses
standard topographic adjustment of radiation and temperature to spatially rescale
remotely sensed ETa, estimated for current conditions in accordance with the Budyko
framework. Calculations were limited by those inputs which could reasonably be
derived from Global Circulation Model (GCM) outputs with minimal assumptions.
Priestley-Taylor potential evapotranspiration was calculated based on topographically
adjusted temperature and radiation, and annual total ETa was subsequently calculated
as the sum of monthly ETa using the Budkyo framework, incorporating a best estimate
of plant available water holding capacity as a tipping bucket. The discrepancy between
modelled and remotely derived ETa under present conditions was used to generate a
cell by cell correction along the Budyko curve which was then applied to GCM driven
future ETa. The approach assumes a consistent large scale spatial pattern of surface
and ground water movement.
EXECUTIVE SUMMARY
A new method is presented which allows the fine scale (250m) resolution projection of
actual evaporation under climate change, by rescaling terrain sensitive modelled
outputs based on Global Circulation Model outputs according to the current remotely
sensed distribution. The mapped outputs capture the local accumulation of water from
surface and sub-surface flow, which is ignored in all downscaled climate projections to
date. Since for much of the year, evaporation is water limited for most of Australia, the
new projected variable indicates where the wetter parts of the landscape can be found.
Under a warmer, drier future climate, this information is likely to be critical to the
identification of potential future refugia.
Climate change refugia for terrestrial biodiversity 149