The future of the hydrological cycle

'A change to freshwater availability in response to climate change poses a more important risk to human societies and ecosystems than warming alone. Changes to the global water cycle and the corresponding redistribution of rainfall will affect food availability, stability, access, and utilization.'

You may think that looking at the hydrological cycle in the future is going a little off topic when it comes to extreme weather events; but a rise in ocean temperatures could offer a greater possibility of hurricane formation over surface waters, and a rise in sea level creates a higher level of vulnerability for coastal populations. It is all connected.

I've linked a recent article by Durack et al. to this post, which caused quite a stir when it was published in Science (2012), as it proposed that for every 1°C warming in surface temperature, the hydrological cycle could intensify by 8(+/-5)%. This means that a 2°C warming in the future, (which isn't unlikely at the current rate of GHG consumption) could see a 24% intensification of the hydrological cycle. This would affect the entire globe, with current wet regions receiving more precipitation and those regions that are drier experiencing more frequent drought.These results were generated by Durack et al. by running sea surface salinity (SSS) data with current climate estimates (CMIP3 scenarios). In my opinion, SSS is a sensible measure to use as it correlates highly with evaporation-precipitation patterns and is far more reliable than the precipitation records; which offer scarce coverage over the oceans and may contain error in gathering techniques (e.g. satellite readings). The higher the salt content observed, the higher evaporation rates.
Of course studies such as this one have been conducted in the past, but the recent CMIP3 scenario data that this model ran with offers a more accurate view of global climate dynamics than has been used previously. Other models ran with more simplistic datasets: as we all know the climate system is very complicated, so leaving out one small factor can impact heavily on results. Of course, the CMIP3 scenarios aren't perfect, but they are the best we have.

The purpose of me drawing your attention to this article is the fact that it is possible that the 1°C of warming that we have experienced over the last century is having a greater impact than we imagine. Although the findings of this study are quite controversial, and in some cases are the complete opposite of other studies; I think that this experiment has ground to stand on. The reasoning behind using SSS as a representative factor of E-P is sensible and the scenario this data was run with is the best that is available. Durack infers that during the last 50 years, the water cycle has amplified by 4%: with another 1°C warming, it could be amplified by a further 8%. This would greatly increase the likelihood of flooding and hurricane formation.

So, as I said, this may have been a little off topic, but I hope you can see how it is an important in relation to the subject. I think Durack et al.'s paper is insightful and although it is definitely not the only work on the subject out there, I hope you can see how it makes a strong case. Anyhow, it's a nice read and also makes you think about how our actions are influencing tomorrow's world, so enjoy...