Modeling the Global Water Cycle
Martin, G.M. 2014. Quantifying and reducing uncertainty in the large-scale response of the water cycle. Surveys in Geophysics 35: 553-575.
The UK's Met Office Hadley Centre researcher continues by identifying the essential components of the way forward, which include "the global water budget and water conservation, the role of model resolution and parameterization of precipitation-generating processes on the representation of the global and regional hydrological cycle, representation of clouds and microphysical processes, rainfall variability, the influence of land-atmosphere coupling on rainfall patterns and their variability, monsoon processes and teleconnections, and ocean and cryosphere modelling."
In light of the many aspects of this broad undertaking, Martin concludes that "continued collaborative activity in the areas of model development across timescales, process studies and climate change studies will provide better understanding of how and why the hydrological cycle may change, and better estimation of uncertainty in model projections of changes in the global water cycle," all of which elements of the gigantic task suggest that we still have a long, long way to go before we will be capable of producing projections of the global water cycle that have even a modest degree of reliability. So until that time, somewhere in the future, we need to take current model projections of the world's water cycle with a good bit of scepticism.