Saturday, May 05, 2012

Connecting Dots With A Bridge

Part of the 350 Campaign to 'Connect the Dots' on climate change.

May 5, 2012 in Melbourne is a cold, drizzly wet autumn day. Nothing out of the ordinary.

The new Solway St. Footbridge. Site of old one is visible to left.

The same may be said of a small footbridge crossing Gardiners Creek at the end of Solway St, in Ashburton. It's quite new, having been opened a couple of months ago. It's certainly better designed than the old one, both in terms of structure and approach (the boarding on the opposite side is where the old bridge was located. The path down to it was a bit precipitate over there, and cyclists were well advised to dismount)

Yes, the old bridge was due for retirement. It happened in January 2011, when it was removed, not by a city engineering crew, but by a flood.

My personal experience of this flood was to watch a curtain of solid rain descend on my house. It rained, solidly, for 12 hours. A local park became an impromptu swimming pool. A bridge was washed away.

Elsewhere, vast areas of Victoria were under water. They remained so for months: the first promising crops after ten years of crippling drought utterly ruined.

This flood was a strange confluence of events: a cold front, crossing the Australian Bight, met a huge mass of moist air heading south, and streamed it into the south eastern corner of Australia.

The cold front was a normal weather pattern. The moist air mass over central Australia came about for two reasons:
  • a strong 'El Nina' event sending a steady airstream from the Indian Ocean over South East Queensland (incidentally also causing massive flooding)
  • a category 5 cyclone (Yasi) which came out of the Coral Sea to strike the North Queensland coast near Cairns. It's power can be gauged from the fact that it was still rated as a cyclone 24 hours later, when it reached Mt Isa. It was this cyclone that came south, bringing its own moisture with it.
  • a bridge was washed away because of...
  • a flooding rain, which was bought by...
  • a cold front, and...
  • a degraded cyclone, squeezing...
  • an already moist airflow south across Australia like a massive uncontrolled garden hose.
Was it just a fluke? Wild weather? Weather is the quality of the day. The systems that caused this minor calamity (and considerably more major catastrophes elsewhere) had lifetimes measured in months.

The crux of this story is about a local insignificant bridge. The theme is about how events sprawled across an entire continent and its surrounding oceans can come to have such a local effect. I've laid out some dots for you to connect as you see fit.


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