Retreating glaciers and thinning snow and ice are the future of New Zealand’s mountains. Climate change is predicted to warm the country’s atmosphere by 1–4°C by the end of the century, altering the natural water cycle—how much is frozen as snow, how much falls as rain, and how much flows in rivers. Climate researchers are seeking to predict what will change, and when. What will be the impact on hydroelectric power stations and irrigation schemes? Which areas will be hit hardest by flooding, or increasingly severe drought? The Deep South National Science Challenge is taking a lead role in helping decision-makers plan for the coming century.