Water availability in +2°C and +4°C worlds

Title Water availability in +2°C and +4°C worlds
Publication TypeJournal Article
Year of Publication2011
AuthorsFung, CF, Lopez, A, New, M
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Start Page99
ISBN Number1364503X
KeywordsClimate change impacts, Ensembles, Global water resources, Macro-scale hydrological model, uncertainty, Water resources stresses

While the parties to the UNFCCC agreed in the December 2009 Copenhagen Accord that a2° C global warming over pre-industrial levels should be avoided current commitments on greenhouse gas emissions reductions from these same parties will lead to a 50: 50 chance of warming greater than 3.5° C. Here we evaluate the differences in impacts and adaptation issues for water resources in worlds corresponding to the policy objective (+2° C) and possible reality (+4° C). We simulate the differences in impacts on surface run-off and water resource availability using a global hydrological model driven by ensembles of climate models with global temperature increases of 2° C and 4° C. We combine these with UN-based population growth scenarios to explore the relative importance of population change and climate change for water availability. We find that the projected changes in global surface run-off from the ensemble show an increase in spatial coherence and magnitude for a +4° C world compared with a +2° C one. In a +2° C world population growth in most large river basins tends to override climate change as a driver of water stress while in a +4° C world climate change becomes more dominant even compensating for population effects where climate change increases runoff. However in some basins where climate change has positive effects the seasonality of surface run-off becomes increasingly amplified in a +4° C climate. ©2011 The Royal Society.