Tuesday, 24 January 2017
4E (Washington State Convention Center )
Global coarse resolution climate models are unable to resolve well the weather systems, local scale topographic features and land surface features such as coastline, islands, urban areas, vegetation and soils. Many important weather systems such as tropical cyclones, east coast lows need much higher resolution than the current IPCCC class global climate models can provide. Dynamical downscaling using global variable resolution CSIRO Cubic Conformal Atmospheric Model (CCAM) provides state of art climate modelling approach able to better capture relevant regional climate features. In this talk we will describe examples of dynamical downscaling focusing on high-resolution (~10km) climate change projections over Queensland region and high-resolution (~20km) modelling of the impact of afforestation in Australia under RCP8.5 scenario.We selected eight CMIP5 global models representing a range of simulated changes over Australin region and used their sea surface temperature (SSTs) and sea ice to drive CCAM model at 50 km global resolution. SSTs were bias corrected for mean and variance to reduce systematic bias introduced by CMIP5 global coupled climate models. CMIP5 time varying radiative frocings such as concentration of greenhouse gases, solar, ozone change and aerosols emissions were used in addition to SSTs and sea ice to complete 8 simulations for period 1950 tom 2099 at 50 km global uniform resolution. Susbsequently global streach version of CCAM was used at 10 km spatial resolution over Queensland region. Eight simulations were completed for period 1980 to 2099 using 6-hourly 3-D data from 50 km simulations and using 1-D spectral nudging approach. We will present results of high-resolution simulations focusing on skill assessment of simulated historical climate by comparing observations with model data and comparing with results from 50 km simulations and CMIP5 models in Queensland region. In addition we will compare simulated climate respoonse focusing on changes in temperature, precipitation and drought conditions using SPI. To assess the impact of afforestation on regional climate in Australia we have developed two contrasting future land-use scenarios for the extensive semi-arid regions of Australia, representative of a) the expansion of dryland crops and pastures (Maximum Crops), and b) the maintenance of crops and pastures only on economically productive lands and the restoration of economically marginal land to woodlands (Partial Restoration). The Maximum Crop scenario represents maintaining cropping and livestock pastures on historically-converted landscapes and an area of planned expansion in northern Australia. The Partial Restoration scenario represents maintaining high-production agricultural land (annual profit >$100/ha) and restoring the remaining less-profitable cropping and livestock pastures to woodlands. The key difference between the land-use scenarios was the proportion of agricultural lands versus woodlands in eastern and southwest Australia.We completed two sets of ensemble simulations using global variable resolution CSIRO Conformal Cubic Atmospheric Model (CCAM) at 20 km spatial resolution over Australian region.An ensemble of three simulations for each land-use scenario for the period 2021–2076 using RCP8.5 emission scenario was completed. The only difference between the two sets of simulations was the land use. Results show that restoration triggers a positive feedback loop between the land surface and the atmosphere, characterised by increased evaporative fraction increased humidity and turbulent mixing in the boundary layer. Cloud formation and convective precipitation are enhanced over the restored areas. The increased evaporative fraction is a direct consequence of the capacity deep-rooted woody vegetation to alter the partitioning of surface energy by accessing soil moisture from the lower soil profile. The increased precipitation provides additional moisture to the soils and vegetation, thus reinforcing the positive biophysical feedbacks. Under the RCP8.5 high emission scenario, restoration reduces the rate of warming and drying. Over restored areas, warming is reduced by 20–40% during the 2023-2076 period. We conclude that large-scale restoration of native vegetation in Australia exerts a moderating influence on the regional climate.
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