Modelling hydrological changes in New South Wales under future climate change

Abstract

Within New South Wales, the Office of Environment and Heritage (OEH) supports climate-change adaptation by working with communities, agencies and other stakeholders to identify and understand regional vulnerabilities. Scientific impact assessments for bushfires, biodiversity, sea level and coasts, floods, soil, human health and water resources have been undertaken. In this study, impacts of climate change on the water cycle and hydrology is investigated. Assessing the impacts of climate change on hydrology is important because changes to the water cycle influence water security, water quality, salinity and groundwater availability. We use the NARCliM (NSW / ACT Regional Climate Modelling) ensemble of climate projections for southeast Australia. This ensemble is designed to provide robust projections that span the range of likely near and future changes in climate (Evans et. al. 2014).The water balance was simulated using the PERFECT model (Littleboy et al. 1992) which is a daily time-step model that predicts surface runoff, infiltration, soil evaporation, transpiration, profile drainage and recharge. PERFECT was applied at a 10km resolution across NSW to predict surface flows and groundwater recharge. Maps and graphs from this modelling form part of the NSW Climate Impact Profile which provides an assessment of projected biophysical changes across the State. Maps presented show central estimates or arithmetic means of future projections. Bar graphs are used to present projections as ranges of plausible change, illustrating the projections from the twelve individual simulations as well as the central estimate. In the near future, less recharge is predicted across much of NSW, especially in the south east of the State. Considerably less recharge is likely in alpine areas. Some areas of western NSW do show a slight increase in recharge but these increases are considered relatively small. In the far future, recharge is expected to increase across many parts of NSW. Some areas along the Great Dividing Range are likely to experience less recharge to groundwater. The largest impact is the dramatic reduction in recharge in alpine areas. Across much of NSW, surface runoff is projected to increase in both the near and far future. Largest increases are evident in the central west through to the northern tablelands. Largest reductions in surface runoff are projected in both the near and far future for alpine areas in the south of the State. More complex analyses at a resolution on 100m are underway for the ACT and coast catchments of NSW. This analysis will permit allow spatial variability in land use and soils to be taken into consideration in the climate impact assessments. This is not represented in this paper.