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Ensuring utility pole durability in a changing climate

Richard George, CEO of Polesaver, examines the effect of climate change on the lifespan of wooden utility poles

Climate change, along with its social and economic effects, remains a significant global issue. Despite its historical presence, the increased frequency of extreme weather events, as noted by the World Meteorological Society [1], is becoming more commonplace.

Utility companies all over the world have established maintenance programmes for utility poles to prevent their failure and therefore any disruptions to energy supplies this could cause. That includes planning for extreme weather. But, apart from more extreme weather patterns, rising average temperatures also cause other changes in nature that can influence the longevity of utility poles.

Most utility poles are still made from wood, pressure treated with a preservative such as Pentachlorophenol, CCA, Copper Napthenate, ACQ, etc. to protect against rot, fungi and insects. Being a readily available renewable resource and an easy to install structurally strong material makes wood the preferred choice for utility poles in many countries. Today, there are between 160 and 180 million wood poles in the U.S. and 5 million of the estimated 7 million utility poles in Australia are wood poles. [2]

Changing growing conditions

As a natural material, wood is susceptible to changes in weather conditions both during the growing phase of the tree and its life as a utility pole. A study [3] found that the growth of forests in Central Europe has accelerated since the 1870s due to rising temperatures, an extended growing season and an increased supply of nutrients like nitrogen and CO2. Trees put on most of their growth early in the season (springwood). Springwood has thinner cell membranes and is less dense than material produced later in the growing season. Unfortunately, accelerated growth in the early season can result in a weaker structure overall [4]. This can have a significant impact on the lifespan of a utility pole made from this wood.

Image of tree canopy to illustrate the environmental benefits of Polesaver.

Not only is this faster grown wood less strong, lower wood density, strength and durability also decreases its natural resistance to decay. The decay of wood poles depends on material properties, soil properties, and local climatic conditions. The main climate parameters that affect the decay of wood are humidity and temperature [5]. A raised moisture content makes water freely available for fungi to establish and grow, causing the wood to decay quicker than in drier conditions. Temperatures between 5 and 65 degrees Celsius are considered to support fungal growth [6] Climate change with increased rainfall and rising temperature is therefore an important factor in the higher rate of wood decay.

The impact of extreme weather

Faster grown, weaker wood, combined with perfect conditions for fungal growth, can cause wooden utility poles to fail earlier than expected, especially under extreme weather conditions like hurricane force winds. These poles are more likely to get blown over, especially where there has been loss of strength due to decay at the mechanically highly stressed ground line section of the pole. While climate change has not increased the number of tropical storms (it may actually have decreased [7]), the intensity of the storms has grown. According to the UN’s climate body, the IPCC[8], it is “likely” that a higher proportion of tropical cyclones across the globe are reaching categories three to five.

Just like more flooding, extreme droughts are also a consequence of climate change in some parts of the world. Where excess moisture can reduce the useful lifespan of wooden utility poles, the polar opposite, droughts, can also be harmful. During prolonged droughts, the soil around utility poles can become significantly dry. As the moisture content in the soil decreases, wooden poles can lose moisture, leading to drying and shrinkage of the wood. This can result in the contraction of the wood fibres, making the pole more susceptible to cracking and splintering. Long dry spells can lead the wood to become brittle and more prone to breakage under stress or load like power lines or other equipment. A moist, not wet, wooden utility pole retains more flexibility and is less likely to break under loads and strong winds.

The impact of extreme weather

Droughts, heat and tropical storms are not a new phenomenon. The extreme nature of them, influenced by climate change, is. Modern engineering has to take into the account the long term structural integrity issues with wooden utility poles at the project design stage.Polesaver Permanent Barrier

Wood, if properly sourced, prepared, preserved and maintained, is still one of the best suited materials for utility poles. Polesaver is a wood protection specialist and can advise on the best options to mitigate the impact of global warming on wooden utility poles. Find out how Polesaver has helped utility companies to achieve their goals.

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