Factoring Global Warming into

Design Flood Estimation

Ashish Sharma and Conrad Waskoa.sharma@unsw.edu.au

Water Research Centre, Civil and Environmental Engineering

UNSW, Sydney, AUSTRALIA

http://www.civeng.unsw.edu.au/staff/ashish.sharma

with help from Seth Westra, Fiona Johnson, Fitsum Woldemeskel, Raj Mehrotra and many more

AcknowledgementsAustralian Research Council

Australian Bureau of Meteorology

Where I am from

Current Scaling StudiesP

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Inte

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Temperature

Pre

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n In

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Time (hours)

Our StudyP

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In

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Time (hours)

Pre

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Inte

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yTime (1 hour)

1.

2.

3.

Scaling of Fractions

Pre

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Inte

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yTime (1 hour)

Pre

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Time (1 hour)

Less Uniform Within Storm Patterns

Pre

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Time

Spatial patterns

Spatial patterns

More concentrated with higher temperatures

Pre

cip

itation Inte

nsity

Flow routing

𝑑𝑆

𝑑𝑡= 𝐼 − 𝑄

With non-linear storage

𝑆 = 𝑘𝑄𝑚

And catchment size governed by

𝑡𝑐 = 0.76𝐴0.38

Impact on Flooding

m = 0.6, 0.7, 0.8, 0.9, 1

tc = 1, 2, 4 hours

A = 2, 12, 80 km2

For 5 degree increase

1 hour (2km2)

Antecedent Conditions

Antecedent Conditions

𝐴𝑃𝐼 = 𝐾𝑃𝑡−1 +⋯+ 𝐾𝑇𝑃𝑡−𝑇

[ K ]

Consistent

increase

Consistent

increase

Consistent

decrease

Antecedent Conditions

𝐴𝑃𝐼 = 𝐾𝑃𝑡−1 +⋯+ 𝐾𝑇𝑃𝑡−𝑇

[ K ]

Consistent

increase

Consistent

increase

Consistent

decrease

• Colder days = more uniform temporal/spatial patterns

• Warmer days = more non-uniform temporal/spatial patterns

• #Cold-days/#Warm days decreasing!

• Patterns becoming overall more non-uniform

Leads to flood increases in urban settings even without changing storm volume (intensity)

Added changes regionally due to changed antecedent conditions

May be countered by evaporation increases in large catchments – but urban floods will continue to increase!

Conclusions

Factoring Global Warming into

Design Flood Estimation

Ashish Sharma and Conrad Waskoa.sharma@unsw.edu.au

Water Research Centre, Civil and Environmental Engineering

UNSW, Sydney, AUSTRALIA

http://www.civeng.unsw.edu.au/staff/ashish.sharma

with help from Seth Westra, Fiona Johnson, Fitsum Woldemeskel, Raj Mehrotra and many more

AcknowledgementsAustralian Research Council

Australian Bureau of Meteorology