Climate change is likely to impact the Australian continent by changing the trends of rainfall, increasing temperature and affecting the accessibility of water quantity and quality. The problem of future water resources availability in Australia has drawn the attention of many researchers to investigate this matter for planning and control purposes. This study presents the future climate change impact on streamflow variability in the contributing catchment of the Goulburn River at Coggan, Hydrologic Reference Stations (HRS) in New South Wales, Australia. Goulburn River catchment distributed over 3402 km2 area and it forms the whole western part of the Hunter River catchment which is the largest coastal catchment in NSW. The Australian HRS network represent ‘living gauges’ that enable the long-term investigation of water resources availability in the contributing catchments. The impact of future climate changes on the corresponding catchments of the HRS is then of great interest, for planning and management purposes, to investigate how climate change will impact the availability of future water resources in these regions.
The HBV conceptual model is applied to simulate the discharge at Coggan HRS for two future periods, mid (2046-2065) and late (2080-2099) of the current century.Daily observed rainfall, temperature, discharge and monthly mean potential evapotranspiration from the contributing catchment of Coggan HRS are used to run, calibrate and validate the HBV model prior to the simulation process. The modelling performance was assessed using three efficiency criteria including Nash-Sutcliffe efficiency (NSE.), relative volume error (VE) and the coefficient of determination (r2). The calibration and validation results revealed a good modelling performance which indicates that the model could be used successfully to simulate the future discharge at Coggan HRS. The downscaled and bias corrected future rainfall and temperature from a multi-model ensemble of eight Global Climate Models (GCMs) from the CMIP5 model under two Representative Concentration Pathways, RCP 4.5 and RCP 8.5 are used to force the HBV model to simulate the future streamflow at Coggan HRS. The CSIRO and the Australian Bureau of Meteorology explained that the GCMs used in the present study represent the best eight GCMs out of 40 GCMs of the CMIP5 that can be used effectively to investigate the Australian future climatic conditions especially for the impact assessment studies.
Results show a clear rainfall-runoff reduction trend across the contributing catchment of Coggan HRS for the mid (2046-2065) and late (2080-2099) of the 21st century under the two climate scenarios as compared to the control run. The results are also in well-match with the streamflow reduction trend provided by the Australian Bruere of Meteorology through the step change analysis of the historical observed mean annual streamflow. The findings of this study will be helpful for local communities and decision makers to manage the usage of future water resources in the contributing catchment such as irrigation, domestic and even drinking by taking into consideration the low flows situation.