Climate change means more rain but less water in rural rivers: study

Sydney: Soaring temperatures driven by climate change are whipping up ever-more intense storms inundating cities with flash floods but leaving the countryside and crucial agricultural land parched, an Australian study has found.  

Researchers at Australia's University of New South Wales (UNSW) found that while hotter weather sparked heavier storms leading to floods in built up areas, it also reduces moisture in the soil, which then quickly absorbs any excess and reduces water flow in rural rivers. "So when the big rainfall events... do fall, a bigger proportion of them are stored up in the soil, so you have a lesser proportion coming out as flows," UNSW professor of hydrology Ashish Sharma told AFP Tuesday.

Experts say decreases in waterways in farming areas threatens agriculture and food security, requiring urgent attention amid a forecast rise in the global population by 23 percent to nine billion over the next two decades. Meanwhile, they point out that city infrastructure is struggling to cope with the harsher downpours, with flood damage worldwide costing more US$50 billion in 2013 -- a figure expected to double in the next 20 years.    

"It's a double whammy," said the paper's lead author Conrad Wasko from UNSW. "People are increasingly migrating to cities, where flooding is getting worse. At the same time, we need adequate flows in rural areas to sustain the agriculture to supply these burgeoning urban populations."  

The extensive analysis, published Friday in the Nature Scientific Reports, is based on data from nearly 50,000 rain and river monitoring sites across 160 countries. Whereas extreme "once in a lifetime" floods are causing increasingly large water flows, regular cyclical inundations are having less and less of an effect on the water table, Sharma said.   

He added that even though the increase in intensity of storms varied around the globe, a persistent finding in the research was that more rain did not translate to more water in river systems. "One thing that came out consistent was the change in rainfall was much more than the change in flow", Sharma added.  

The paper's authors said engineering solutions were required to adapt to the change in environment. "In places like Arizona, or California, the Netherlands, or the Snowy Mountains Scheme (Australian hydroelectricity system), these things happened because of civil engineers," Sharma said. "We felt that the way the natural system was working was not consistent with where we want the population to be so we engineered an outcome... and we are benefiting from all the work that was done so many years ago."