Kansas City on ice

January 29 marked the arrival of an historic ice storm that devastated large portions of the Midwest. One of the hardest hit locales was the Kansas City metropolitan area. Officials called it the worst natural disaster in local history. The results were as instructive as they were devastating.

What happened

The storm began on January 29 and lasted through the 31st. An unusual weather pattern brought moisture in a flow that stayed more or less in place for the duration of the storm. Due to low air temperatures, a layer of ice ½ to 1 inch thick coated everything in the area. The effect that this much weight has on tree limbs doesn't need explaining. Mostly, it was only a question of whether branches would bend or break.

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Though the thought of ice storms may evoke mental images of branches and whole trees crashing violently through lines (in fact, that does happen), the reality in most cases is somewhat different, though sometimes no less spectacular.

As ice accumulates, tree branches sag, drooping onto power lines. According to Jerry Borland, executive editor of Transmission and Distribution World magazine, this is what causes most outages in ice storms. The branches cause a short, or fault, when they touch the lines. If no protective measures were in place, the arcs generated by the electrical current would eventually melt the line, causing it to break. To prevent this, utilities install in-line fusible links, as well as fuses on transformers, that will blow when a fault occurs. This results in a loss of power, and each one of the blown fuses must be replaced manually to restore service. That's why it takes so long to regain power after a widespread event. But it's easier than repairing broken lines, which would take even longer.

In the end, most customers in the Kansas City area were without power. Utility crews from all across the Midwest were called in to help. According to Borland, “The normal workforce for Kansas City Power and Light (the largest utility in the KC area) is 107 crews, which amounts to 489 people. The ice storm resulted in KCP&L bolstering their workforce by an additional 738 crews, totaling an additional 2,300 people. KCP&L recorded the most outages with 285,000 total reported outages,” but was not the only utility severely affected.

Lessons learned?

The destruction clearly showed that areas where line clearance had occurred recently were less prone to destruction. As much as people complain about what's done to trees around power lines, it's a valuable thing, as this storm proved. Afterward, area utilities were criticized for not trimming aggressively enough. (Sometimes, you just can't win!) According to Borland, tree trimming is one of the largest line items in utilities' budgets, and often it's difficult to adequately fund trimming operations.

Perhaps more interesting were the clear differences among tree species regarding structural damage. Mike Dougherty, urban forester and owner of Tree Management Company (Lenexa, Kan.), saw first-hand how some trees fared better than others. Dougherty lists the following susceptible species and causes of failure:

  • Silver maple: Soft wood resulting in mid-limb failure; forks/V-shaped crotches and weak branch attachments resulting in splits; re-sprout failures from previous topping practices.

  • Red maple (cultivars): same failures as silver maple.

  • River birch: Soft wood resulting mid-limb and trunk failure.

  • Green and white ash (cultivars): Forks/V-shaped crotches and weak branch attachments causing splits.

  • Redbud and dogwood: Forks/V-shaped crotches and weak branch attachments causing splits.

  • Ornamental pear (cultivars), primarily Bradford: Co-dominant stems, forks/V-shaped crotches causing splits, often to the ground, destroying entire tree.

  • Siberian elm: Brittle wood causing snaps/breaks mid-limb; re-sprout failures from previous topping practices.

  • Willow and cottonwood: Soft wood resulting in mid-limb and trunk failure.

Looking at Dougherty's list, you see a mix of “old” species, as well as some currently popular types. Dougherty asserts that just as we now are paying for poor planting choices made decades ago (such as Siberian elm, which was widely planted as a replacement for American elms ravaged by Dutch elm disease), many of our current choices will create similar problems in 20 to 40 years.

Newer popular species, such as red maple and river birch, are planted by the thousand and are not among the more structurally sound trees. People just don't realize what a problem they may be creating, according to Dougherty, because these specimens aren't old and large enough to do much damage yet. That may be too generous, however. Despite the wide recognition of their weak structures, people continue to plant silver maples and Bradford pears in great numbers in urban areas.

Of course, this is not to say the species on Dougherty's list have no place … just not next to houses and power lines!

Too often, we ignore long-term or infrequent problems, to our own peril. Although an ice storm this severe is considered a rare weather event, a look back at the not-so-distant past shows that destructive weather events — the kind that should make you reconsider that Bradford pear you're about to plant next to the house — aren't really that infrequent.

A freakish October 1996 snowstorm caused widespread damage and power loss in Kansas City because trees had not yet shed their leaves for the winter. The foliage caused much more snow than normal to weigh on the branches, bringing many of them down. This followed a destructive ice storm that occurred in the early 1990s. Three catastrophic weather events in one decade makes a strong case for careful plant selection.

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