One of the most significant effects of a changing climate is the intensification of the hydrological cycle. This will almost certainly exacerbate the ‘boom and bust’ cycle of water availability familiar to Australians, exemplified by our experience over the last decade as we switched suddenly from our deepest ever drought to our biggest ever rains.

Intensification of the hydrological cycle presents particular challenges for planners and managers who need to understand how to adjust water policy, water management rules and water supply capacity in the future. Forecasting changes in water demand has always been difficult due to uncertainties in population growth and anticipated water use behaviour. Estimating the supply side of the water balance equation was simpler when we could assume stationarity in rainfall and stream flow patterns, but in a changing climate this is no longer appropriate. Today, estimating future water availability is harder because we are less certain about how the water balance will change in particular parts of the country at particular times. Harder again, is envisaging how these water balance changes will differentially impact complex urban and rural water supplies and water-dependent ecosystems. These are matters of significant societal importance.

In order to meet these challenges, the climate and hydrological science communities must work together to ensure that our observational, modelling and analysis activities focus on the questions that will have the greatest social, economic and environmental significance pertaining to water resources. The Bureau of Meteorology is attempting to bring both climate and hydrology, and research and services, closer together. In guiding our efforts, we are striving to develop a deeper appreciation of the most significant decisions confronting water policy analysts, planners, managers and users.