Urban Floods ​Intensifying, ​Countryside ​Drying Up ​

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Urban Floods ​Intensifying, ​Countryside ​Drying Up ​

A global analysis of rainfall and rivers by UNSW engineers has discovered a growing pattern of intense flooding in urban areas coupled with drier soils in rural and farming areas.

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Urban flood, Source: Pixabay

Drier soils and reduced water flow in rural areas but more intense rainfall that overwhelms infrastructure and causes flooding and stormwater overflow in urban centres. That’s the finding of an exhaustive global analysis of the world’s river systems by UNSW researchers.

The study by engineers at UNSW, which appears in the latest issue of the journal Nature Scientific Reports, explored how rising local temperatures due to climate change might be affecting river flows. It reviewed data collected from more than 43,000 rainfall stations and 5,300 river monitoring sites across 160 countries.

As expected, it found warmer temperatures lead to more intense storms: a warming atmosphere means warmer air, and warmer air can store more moisture. So when the rains do come, there is a lot more water in the air to fall, and rainfall is more intense.

But there has been a growing puzzle: why is flooding not increasing at the same rate as the higher rainfall?

The answer turned out to be the other facet of rising temperatures: more evaporation from moist soils – which are needed in rural areas to sustain vegetation and livestock – is causing them to become drier before any new rain occurs. Meanwhile, in small catchments and urban areas where there are limited expanses of soil to capture and retain moisture, the intense downpours become equally intense floods, overwhelming stormwater infrastructure and disrupting life.

Global flood damage cost more than US$50 billion in 2013, a figure expected to more than 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%, from today’s 7.3 billion to 9 billion, requiring added productivity and greater water security. The reduction in flows noted by this study makes this an even bigger challenge than before.

Read full article: UNSW Sydney

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