Impacts of climate change on temperature and evaporation from a large reservoir in Australia

Determining evaporation rates is essential for efficient management of reservoirs and water resources, particularly in water-scarce countries such as Australia. Today, it is estimated that open water reservoirs in Australia lose around 40% of their total water storage capacity per year to evaporation. While this loss is of significant concern, the threat of a changing climate has been directing greater focus to how much water will be lost from Australia’s reservoirs in the future. This paper analyses evaporation rates from a large water supply reservoir in South-East Queensland (SEQ), Australia, under current climate and predicted climate change conditions using modelling. Daily meteorological projections from nine global climate models were used in the model DYRESM as the driving forces of the thermodynamics of the reservoir under study. Two future 20-year period simulations were undertaken, one from 2030 to 2050, and the other from 2070 to 2090. The modelled future evaporation rates, as well as water temperatures, were then compared with modelled evaporation rates and temperatures obtained using observed meteorological variables for the period of 1990–2010. The results showed that the evaporation rates from the study reservoir will increase in the future. For the period centred in 2040, the annual evaporation will be approximately 8% higher than the 20-year average annual evaporation estimated for the present climate. A more pronounced increase in evaporation is expected in 2070–2090, with annual evaporation predictions being approximately 15% higher than the baseline evaporation. The main agent behind this increase is higher surface air temperatures in the future. According to the modelling results, the mean annual surface air temperature will grow from the present value of 20.4 °C to 21.5 °C in 2030–2050, and to 23.2 °C in 2070–2090. As a consequence, the mean annual surface water temperatures of the reservoir will increase by 0.9 °C and 1.7 °C in both timeframes, respectively. This will have a significant impact on the evaporation rates, particularly in spring and summer, when the temperature increases will be more significant.