Weather Impacts
Increased temperature is indicated by a steady rise in global average temperatures and a shift in temperature distributions from low extremes (very cold) to high extremes (very hot). Increased temperature raises the likelihood of heatwaves, drought, and wildfires as well as accelerates the intensity of other weather impacts.
Temperature increases generally occur slowly over time and therefore have gradual impacts on pavement assets. Temperature drives freezing and thawing actions in unbound pavement layers, with many State departments of transportation reliant upon accurately predicting when roads will be frozen. Temperature changes have the potential to increase freeze-thaw cycles (when the temperature fluctuates above and below freezing) for pavements, therefore increasing pavement damage. Warmer temperature can also trigger substantial structural failures in the short term (such as buckling due to excessive slab expansion) and long term (such as rutting in asphalt pavement layers).
Increased temperature introduces a high risk for disruption to the function of pavement assets and extreme temperature events still carry the potential to severely compromise pavement structures both in short-term and long-term time frames. In the case of diurnal temperature variations (the variation between a high air temperature and low temperature in a given day) across 24-h periods, thermal fatigue (degradation of a material due to temperature fluctuation) can occur both in flexible and rigid pavements. Thermal fatigue in rigid pavements increases the potential for thermal-related distresses, thermal expansion issues, buckling.. Thermal fatigue in flexible pavements occurs because temperature cycling eventually exceeds the fatigue resistance of the asphalt concrete binder.
Increased temperature that creates dry soils, combined with wind and a high density of trees, shrubs, and other forest material, can create high-risk conditions for a wildfire. Wildfires make pavements unsafe for travel due to extreme heat and may result in landslides that can cover roadways, making pavement assets functionally useless. Additionally, roadway clearing activities needed after wildfire events may cause trucks to have larger-than-normal weight when removing debris, accelerating the pavement system’s structural failures.
Quantifying risk is an important first step in assessing pavements’ resilience against wildfires. The U.S. Department of Agriculture Forest Service has produced the Wildfire Risk to Communities website, which contains resources to help communities understand, explore, and reduce wildfire risk.
Increases in frequency and intensity of precipitation can adversely impact transportation infrastructure, including pavements. Pavement infrastructure is designed to drain storm water away from the surface and unbound material layers. Free-flowing water across a pavement surface poses a safety risk for vehicles, and saturated unbound layers (the base of pavement that provides structural support) reduce a pavement’s structural strength.
Increased precipitation of high intensity and/or duration in urban areas can lead to flooding. Greater urbanization produces more impervious infrastructure systems that increase flooding risk. Flooding can increase the duration and frequency of pavement inundation, which leads to flooded travel lanes, roadway washouts, and pavement deterioration.
An exceeding amount of precipitation also contributes to increased groundwater table and soil saturation, causing events such as landslides. Landslides can cover roadways (making pavement assets functionally useless) or cause pavements to slip away (resulting in full structural failure).
Extreme events, the term for extreme weather events that impact pavements, pose a significant risk that could lead to damage, destruction, and/or loss of life. For pavements, extreme events could lead to temporary functional failure as well as, in some cases, complete structural failure. These events are significant anomalies in temperature, precipitation, and winds that may manifest as heavy precipitation and flooding, heatwaves, droughts, wildfires, and/or windstorms (including tornadoes and tropical storms).
Given the destructive and disruptive nature of extreme events, quantifying pavement assets’ vulnerability and risk of structural failure under extreme-event conditions is very important. Responding to the disruptive threat of weather impacts also requires short-term and long-term adaptation strategies.