Researchers have provided robust evidence that wet regions of the earth are getting wetter and dry regions are getting drier - but it is happening at a slower rate than previously thought.

Dr Jan Zika of the UNSW School of Mathematics and Statistics authored the study, published in Scientific Reports, along with co-authors from the University of Southampton, UK.

The study analysed the saltiness of the world’s oceans.

More rain and outflow from rivers in a region of an ocean means sea water gets diluted and therefore becomes less salty. More evaporation in another region takes away fresh water and leaves salt behind making that region more saline.

The researchers used measurements of salinity throughout the global and deep oceans over the last 60 years to estimate how much global rainfall is changing.

The researchers found that the regions which are currently relatively dry, like most of southern Australia, are likely to get dryer and regions that are relatively wet to the north and south are likely to get wetter. This process is called amplification of the water cycle.

Previous research indicates that amplification of the water cycle, is happening at 7 per cent per 1°C of global warming. The new study estimates that amplification happens at about three to four per cent per 1°C. The research team believe this is probably due to a weakening of the atmospheric circulation which transports freshwater from the dry to wet regions of the globe.

The findings match what has been predicted by models of a warming climate. Those same models predict that as the world gets warmer, wet regions will continue to get wetter and dry regions will continue to get drier.

“If global warming exceeds 3°C, wet regions will likely get more than 10 per cent wetter and dry regions more than 10 per cent drier. This could have disastrous implications for river flows and agriculture”, said Dr Zika.

Co-author Dr Nikolaos Skliris added “The agreement between climate models and observations over the recent past is another important finding of this study because it adds confidence to climate model projections of water cycle amplification under greenhouse gas emission scenarios".

(Images, L-R: 60-year trends in surface salinity - blue areas are getting wetter, red areas are getting drier; Dr Jan Zika)