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| September 06, 2017 Post 86 |
| Wild Weather |
Hurricane Harvey with rain totals of a nearly unbelievable 50 inches has been called historic, unprecedented and catastrophic – an extremely rare 500 year event. Yet commentators are also saying Houston has had three “500 year storms” since 2001. How can this happen? And why are these record events like tropical storm Sandy or Lake Ontario's record flooding of 2017 so much more damaging and costly than in the past? Is it climate change? A vengeful Old Testament Deity? Or lousy urban planning and inept engineering? As usual, there is not one simple explanation.
A 500 year event like Harvey's rainfall has a one in 500 chance of happening in a given year. The 500 years refers to probability, not timing. Though it's very unlikely, that means you could get two of them back to back. Admittedly, there's only a .2 percent probability that you will, but it could happen. Especially if conditions are changing.
100 year floods and storms are a concept that came about in large part because of the insurance industry. The insurance business has to play the odds in order to stay profitable. You calculate how likely an auto crash or a house fire is and charge the premiums accordingly. Hopefully, you guess right and the stockholders get a dividend that year. Since insurance pretty much rules the modern man made landscape, engineers and urban planners also use concepts like 100 year floods as they draw up building codes and zone residential areas.
These probabilities are based on historical data. But as we know things keep changing. As a city grows, more pavement is laid down, and more roofs go in. These impermeable surfaces change run off and drainage patterns. Run off becomes more “flashy” as there is no soil or vegetation to slow flows and allow it to re charge groundwater aquifers. Houston like most big cities in North America has been sprawling and 'hardening' the earth for many decades. It's growth has been mostly unplanned and careless of long term consequences. When approximately a sixth of the volume of Lake Erie fell on it in five days trouble followed.
One preliminary estimate suggests Harvey will be the expensive U.S. natural disaster ever. Here along the lake shore people continue to build large elaborate homes in low lying areas prone to lake water intrusion. Their answer to record high levels is more pumps, more seawalls and more tax payer bailouts.
As I have written previously weather patterns may be changing. “Blocked” weather systems that sit in one spot and dump rain appear to be happening more frequently since the 1980's. Peer reviewed research suggests that these stalled storm systems may be related to reduced ice cover in the Arctic that has impacted the patterns of jet stream movement.
This spring saw the wettest May ever in the Great Lakes basin.As I write this a record breaking heat wave and and wildfires are hitting the west coast. What used to be a 500 year event based on historical data is now a 50 or 100 year event according to Dr. Kevin Trenberth who has studied rain fall and climate change for many years.
We cannot 'engineer' our way out of this mess. We simply cannot build all the dikes and seawalls and bigger drainage channels to take care of this problem. If we continue to destroy buffers like forested slopes and wetlands and we don't change our behavior we are doomed to a downward spiral of short term profits for the concrete industry and the big engineering firms and long term ecological bankruptcy as our soils wash into Lake Ontario.
We must acknowledge the role of climate change and act to reduce green house gas emissions. We can do it through carbon taxes, support for renewables, and increased efficiency. We cannot do it without a change in current federal policy. This I regret to conclude is not an opinion. It's a fact.