Study reveals effects of climate change on rural streamflows

Posted 5 September 2017

View of riverbank and river with low water levelsWhile global warming will likely cause floods in urban areas due to intense rainfall, surface water flows in rural areas are set to decline, according to a new study from the University of New South Wales.

The study analysed data collected from 43,000 rainfall stations and 5300 river monitoring sites across 160 countries to assess how rising temperatures will affect river flows.

The aim of the research was to determine why higher rainfall isn’t equating to more water in rivers, focusing on natural surface-water sources in relatively warm climates such as Australia and the US. 

The research showed soil moisture is declining due to increased temperatures, resulting in less rainfall converting into streamflow, UNSW Hydrology Professor Asish Sharma told Farm Online.

“We took the top 10 flow events in each river and found that, on average, flows are reducing. This is totally contrary to what you’d expect, because clearly intensity of rainfall is going up in these places,” Sharma said. 

“By deduction, we concluded that evaporation losses are rising and therefore the soil must be drier. Many other studies have demonstrated global warming has reduced soil moisture. That means the amount of rainfall converted into streamflow is falling.

The fact that we relied on observed flow and rainfall data from across the world, instead of uncertain model simulations, means we are seeing a real-world effect – one that was not at all apparent before.”

Furthermore, drier soils are expected to have a compounding effect on water security; lower stream flows will supply less water to dams, while drier soils will require more demand for food production irrigation. 

Sharma said one of the issues with erratic flooding in rural areas is the deficit of water in catchment dams. 

“If floods are reducing, and that includes average-sized events and not just the once-in-a-lifetime floods, we are in trouble,” Sharma said.

“It is the smaller floods that fill dams. The one-in-100 year events are too big and aren’t captured in storages.”

Sharma said managing the problem will require more effective policy focusing on urban design and water security infrastructure. 

“There are problems associated with large engineering projects, and no one likes messing with nature. But I don’t see a simple solution to the problems created by global warming. Global efforts to reduce emissions will only benefit us over a long time period. We need more localised solutions,” Sharma said.

“We may need to do what was done to make previously uninhabitable places liveable – engineer catchments to ensure stable and controlled access to water.”
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