In Cities, Flooding and Rainfall Extremes to Rise as Climate Changes

Cities face harsher, more concentrated rainfall as climate change not only intensifies storms, but draws them into narrower bands of more intense downpours, UNSW engineers have found.  This has major implications for existing stormwater infrastructure, particularly in large cities, which face higher risks of flash flooding.

In the latest issue of Geophysical Research Letters, doctoral student Conrad Wasko and Professor Ashish Sharma of School of Civil and Environmental Engineering at the University of New South Wales show the first evidence of storm intensification triggering more destructive storm patterns.

"As warming proceeds, storms are shrinking in space and in time," said Wasko, lead author of the paper.  "They are becoming more concentrated over a smaller area, and the rainfall is coming down more plentifully and with more intensity over a shorter period of time.  When the storm shrinks to that extent, you have a huge amount of rain coming down over a smaller area."
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Most urban centers have older stormwater infrastructure designed to handle rainfall patterns of the past, which are no longer sufficient.  "The increase is especially noticeable in urban centers, where there is less soil, unlike rural areas, to act as a dampener," said Sharma. "So there is often nowhere else for the water to go, and the drainage capacity is overwhelmed. So the incidence of flooding is going to rise as temperatures go higher."

Wasko, lead author of the paper, said scientists have long suspected that the intensity of rainfall would be boosted by climate change, as the warming air raises the carrying capacity of moisture. But while extreme rainfall has been rising, little was known about the mechanisms causing it.  The latest study shows that storms are changing in spatial terms.

Read more at In Cities, Flooding and Rainfall Extremes to Rise as Climate Changes