Water availability in +2°C and +4°C worlds.
While the parties to the UNFCCC agreed in the December 2009 Copenhagen Accord that a 2°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 run-off. However, in some basins where climate change has positive effects, the seasonality of surface run-off becomes increasingly amplified in a +4°C climate.
Tyndall Centre for Climate Change Research, School of Geography and the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK. fai.fung@ouce.ox.ac.uk
Fai
F
Fung
Ana
A
Lopez
Mark
M
New
D002245:Carbon Dioxide / Q000737:chemistry; D057231:Climate Change; D003247:Conservation of Natural Resources; D018534:Earth, Planet; D004463:Ecology; D005618:Fresh Water; D057232:Global Warming; D008962:Models, Theoretical; D013696:Temperature; D014867:Water / Q000737:chemistry*; D014881:Water Supply
D014867:Water; D002245:Carbon Dioxide