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Flooding again

Apr 24, 2017

The widespread flooding across Hamilton last Thursday confirms that all parts of the city are threatened by the increasingly severe rainstorms resulting from global climate change. But while the over 70 millimetres of precipitation that day was a significant storm, it falls far short of the cloudbursts that clobbered the eastern part of the city several years ago or the one that flooded over 2000 homes in Burlington the three summers ago.

Scientists are now linking unusual weather events across Canada and other parts of the northern hemisphere to the rapid disappearance of the Arctic ice cap and they fear extreme precipitation will worsen as that melting continues. Global temperature records were broken again last month according to just-released US government data.

“This was the second highest for March since global temperature records began in 1880,” reported the National Oceanic and Atmospheric Administration. “March 2017 marks the first time since April 2016 that the global land and ocean temperature departure from average was greater than 1.0°C (1.8°F) and the first time the monthly temperature departure from average surpasses 1.0°C (1.8°F) in the absence of an El Niño episode in the tropical Pacific Ocean.” February also came in as the second hottest ever.

El Nino episodes drive up global temperatures and often intensify storms across North America. The last one ended in June 2016 and was widely credited with pushing world temperatures to three consecutive annual records, but even after El Nino ended, the mercury has remained high. NOAA is warning that another may begin this fall.

The city spent tens of millions to reduce flooding risks after the 2009 storm that dumped up to 100 mm on the lower east end and shut down the Red Hill Parkway four times in two years. That parkway was disrupted again by last week’s deluge, but it was Dundas that was hit hardest where Spencer Creek, the region’s largest, flows through the centre of the low-lying valley town and imposes major management challenges.

Flows in Sydenham Creek – a tributary of Spencer – appears to have been as much as 50 percent higher than anything in recent memory, and resulted in the creek erupting out of its normal channel onto adjacent areas including businesses. Flooding also took place in Burlington, Stoney Creek, and Flamborough.

For past major storms, the city has offered compassionate grants of up to $1000 to each flooded residence, spending over $5.2 million over the last decade. Another municipal measure is grants of up to $2000 to cover homeowner costs of installing backflow valves – a program started in 2009 that has consumed well over $20 million including $3.5 million last year.

The most severe rainfall inside the boundaries of Hamilton took place in 2012 when over 160 mm fell in six hours in the upper Stoney Creek and Binbrook area. It also flooded homes, but much of its impact was absorbed in the largely rural landscape. Under pre-climate change standards a storm that size should only occur once every 1000 to 5000 years.

Arctic temperatures have climbed much faster than the global averages because the reflective ice is being replaced by dark land and ocean surfaces that absorb far more of the sun’s energy and result in a vicious circle of rapid warming. Ice cover this spring has shrunk to its lowest spring level ever recorded with ice volume even more diminished.

Climate researchers believe the jet stream that carries weather systems across the northern hemisphere has been disrupted and weakened by the much lower temperature difference between its northern and southern sides. This is generating bigger loops in the jet stream that take warmth north and bring extreme cold further south, as well as blocking patterns which make both drought and rainfall more persistent.  

“Blocking patterns caused by slow-moving meanders of the jet stream have been firmly linked to some devastating events, including the 2010 summer floods in Pakistan, which killed 2,000 people and affected 20 million,” reports a Guardian analysis, “and also the searing heatwave in Russia in the same year, which killed 50,000 people and wiped out $15 billion of crops.”

Last month the World Meteorological Organization warned that climbing global temperatures have pushed the planet “into truly uncharted territory”. Their assessment reported “unprecedented heat across the globe, exceptionally low ice at both poles and surging sea-level rise.” 

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