Reason behind that sinking feeling

A recent study published in the latest issue of the journal Scientific Reports, shows how rising local temperatures due to climate change might be affecting river flows across the world. The study’s finding is drier soils and reduced water flow in rural areas, but more intense rainfall in urban areas that leads to serious flooding, stormwater clogging and strain on city infrastructure.

The study, conducted by engineers at the University of New South Wales, in Sydney, shows how rising local temperatures due to climate change might be affecting river flows.

The finding is an exhaustive study of the world's river systems, based on data collected from more than 43,000 rainfall stations and 5,300 river monitoring sites across 160 countries.

The researchers found that warmer temperatures lead to more intense storms, which makes sense: a warming atmosphere means warmer air, and warmer air can store more moisture.

So when the rain comes lashing down there is a lot more water in the air and hence rainfall is more intense. But it’s puzzling why flooding is not increasing at the same rate as the heavier rainfall.

The answer turns out to be the other facet of rising temperatures: more evaporation from moist soils is causing them to become drier before any new rain occurs — moist soils that are needed in rural areas to sustain vegetation and livestock.

Meanwhile, in small catchments and urban areas, where there are limited expanses of soil to capture and retain moisture, the same intense downpour leads to intense floods, overwhelming stormwater infrastructure and disruption of public life.

“Once we sorted through the masses of data, this pattern was very clear," said Ashish Sharma, a professor of hydrology at UNSW’s School of Civil and Environmental Engineering.

Conrad Wasko, lead author of the paper and postdoctoral fellow at UNSW’s Water Research Centre, said that people are increasingly migrating to cities, where flooding is getting worse. At the same time, we need adequate flows in rural areas to sustain agriculture which supplies food to these burgeoning urban populations.

Global flood damage cost more than $50 billion in 2013; this is expected to double in the next 20 years as extreme storms and rainfall intensify and growing numbers of people move into urban centres.

Meanwhile, global population over the next 20 years is forecast to rise another 23 per cent from today’s 7.3 billion to 9 billion — requiring added productivity and hence greater water security. The reduction in flows noted by this study makes this an even bigger challenge than before.

(Source: https://www.sciencedaily.com/releases/2017/08/170814092941.htm)