Principal Investigator Tony Jakeman Project s31

Centre for Resource and Environment Studies Machine CM

Co-Investigators David P Hansen, David A Post, Sergei Schreider and Wei Ye

Centre for Resource and Environment Studies

Dynamic Separation of Catchment Water Balance

The aim of this project is to perform dynamic separation of catchment water balance using rainfall, temperature and stream flow time series. The computer program, IHACRES, will be applied to a large number of catchments (of different sizes and in different hydrodynamic regimes) world wide. The outcome will be a better understanding of how catchments respond to climatic and land use changes.

What are the basic questions addressed?

IHACRES has proven to be a relatively simple but effective model, incorporating the basic physics and having around six parameters, that has been shown to be applicable in a wide variety of hydroclimatologies. The accuracy of IHACRES compares extremely favourably with all other, including more complex models, which are in common use for calculating evaporation and streamflow runoff from rainfall data. A number of catchments in different climates, and with different vegetation cover, are being studied. It is hoped that this will lead to improvements in the process descriptions in IHACRES and that the model can then be incorporated into global climate models, as well as being used to assess the effects of prescribed vegetation changes on the water balance in any given catchment.

What are the results to date and future of the work?

The CM-5 has been used over the last 12 months to calibrate the IHACRES model for a large number of catchments. For example, the model was calibrated for several catchments in the Clarence River Basin in north-eastern NSW for the period over which stream flow records exist (approximately 20 years). The model was then used to simulate the streamflow over the entire rainfall record from the region (approximately 100 years). It has therefore been possible to assess the natural variability of runoff in the Clarence Basin Catchment for several purposes, including water supply. The CM-5 has been used to calibrate the model for several other catchments including various sub catchments in the Murray-Darling basin, relatively dry catchments in Western Australia, as well as benchmark catchments in Australia and the United States. Some of these calibrations have been used as parameters for these regions in Global Climate Models (such as CCM2, see project r52).

What computational techniques are used and why is a supercomputer required?

The bulk of the calculation involves parameter estimation using an instrumental variable algorithm. A large parameter space needs to be searched and this can be efficiently carried out in parallel. The CM-5 provides an efficient platform for calibrating the IHACRES model.