The total amount and distribution of water in the atmosphere is very sensitive to temperature such that global warming is expected to lead to substantial changes in all aspects of the water cycle.
There are some robust features of the response of the water cycle to climate change for which there is general agreement, including an increase in global mean precipitation, enhanced fluxes of water from the subtropics to higher latitudes, and increases in the magnitude of extreme precipitation events. But there are several other aspects of the response for which there is little certainty and only incomplete theoretical frameworks on which to build. For example, changes in the circulations associated with heavy precipitation events and the rate of drying of subtropical land regions are difficult to constrain with current climate models, but could have important societal impacts. The scientific challenge spans a wide range of time and space scales from small-scale microphysical processes (including the effects of aerosols) to large-scale radiative forcing and circulation changes. A proper understanding of societal impacts and the vulnerability of water resources involves the full complexity of the water cycle over land. Progress on such problems will come from improved observational and modelling capabilities, but will also require a better overall understanding of the dynamical controls on the global water cycle.