Although temperatures on earth have risen many times in the past millions of years, more recent documented trends in temperature have been abnormal. Several scientific studies have shown more pronounced rises in global temperatures over the last few decades, especially been since 1970s. Ice core samples, rock and tree rings show signs of a changing climate. Ice sheets continue to shrink, oceans are getting warmer, and glaciers are retreating. The primary cause of this rapid global temperature increase has been attributed to human activity. According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), human-caused climate change has increased the frequency and intensity of heatwaves since the 1950s and additional warming will further increase their frequency and intensity.
This explains why we are experiencing more recorded heatwaves that are also last longer, are more frequent and more intense. Heat waves are basically an extended period of excessively hot weather with often high humidity.
Heat waves tend to affect those in urban environment more intensely due to the distinct nature of urban climates. So, what makes urban climates different? In urban environments, natural surfaces are transformed into impervious areas that release anthropogenic heat, which is simply a term referring to heat generated by human activity, chiefly pollution. Temperatures are usually higher in these environments. Combined with other buildings and surfaces that trap heat, this compounds the effect of heat waves, making such environments hazardous to human health and public safety.
The contribution of the construction sector to greenhouse gas emissions have widely been shown to increase the average global temperature. Then there is the greenhouse-gas effect. The construction industry is a major culprit because it consumes large amounts of energy when it produces materials such as steel and concrete. Concrete, when used as in building project, reflects more sunlight and slowly releases heat during the night, leading to high temperatures relative to neighboring areas. Buildings also consume large amounts of energy due to heating, cooling and lighting. The deconstruction process of buildings result in materials being disposed of at landfills, which emit copious amounts of gases and emissions.
Human driven activity such as burning natural resources (in the form of coal, oil and natural gases) for energy emits gases into the atmosphere. This traps heat and warms the planet. Densely built and populated cities absorb part of the heat and further trap heat within concrete and asphalt. This heat is trapped nearer the surface and people will typically feel the heat more intensely. The effects of heat waves in urban areas can spark a feedback loop. Longer, hotter summers would mean an increase in electricity demands for air cooling. This leads to more gas emissions into the atmosphere, which does contribute to worse heatwaves.
Civil engineers have a responsibility to mitigate the impact heat waves have on cities. It is important to note that the factors affecting heat waves in cities remain complex to study. In the construction sector, various building materials with diverse properties are used. Obviously due to these varied properties, each material will respond uniquely to heat. The degree of urbanization, land use patterns, heat sinks and moisture content make it even more challenging to determine, conclusively understand and develop patterns that can be used to combat the effects of heat waves.
Heat waves negatively impact water systems, infrastructure, transportation to name a few areas. Metropolitan areas experience significantly warmer temperatures than their surrounding rural areas, particularly at night and during heat waves. One reason is because of the moisture in soils that help regulate heat, does not exist to the same level as it would in rural environment (it has been covered by roads and structures). Vegetation and natural landscapes, provide cooler environments against heat by proving shade and releasing water from plants leaves. In densely built environments, this benefit is minimal and almost non-existent.
Heat waves can significantly affect health of the occupants in built environments. In areas with more dense construction, lower green spaces, heat absorbing materials and poorly ventilated environments are more at risk to have their health negatively impacted. There are however strategies civil engineers can employ to mitigate impact of heat waves on the built environment. Strategies should be geared towards limiting heat sources and enhancing heat sinks within the built environment. One plan of action building green infrastructure to limit pollutants, improve air quality, and enhance the cooling effect affect by providing environments with proper shade.
Another is the use of materials that reflect a higher percentage of light (albedo materials) and demonstrably reduce the impact of heat waves. Roofs, wall, ceilings can be built with high albedo materials. In areas exposed to extremely high temperatures, it might be tricky to implement albedo materials. It must be done so expertly, otherwise, it can lead to increased temperatures in certain areas and thus negatively affect pedestrians.
Regulating building heights to improve airflow can be used as a strategy to combat heat waves in urban environments. The use of insulating materials, PCM, and designing buildings to optimize glazing have all been proven to help reduce the negative effects of heatwaves.
There is also the strain it puts on services such a transportation and energy systems. Peak electricity demands tend to correlate with higher temperatures. For example, refrigeration systems use more electricity during these times. It can put strain on the energy grid which can lead to a spike in energy prices.
So, why does this all matter to civil engineers? Heat waves affect a few key areas of concern, namely infrastructure, public safety and comfort and long-term sustainability.
Infrastructures made with certain construction materials are more vulnerable when exposed to higher temperatures. An example is asphalt. This common road construction material is formed of aggregates and binders (usually bitumen). Because bitumen is a byproduct of oil, it is very sensitive to high temperatures and softens under extremely high temperatures. In fact, the temperature of the asphalt usually significantly exceeds that of the air. So, if a heatwave produces a temperature of 40 degrees Celsius, then that of the asphalt can be 60 degrees Celsius. Bitumen softens at around 50 degrees Celsius. You can see how this compromises the safety of drivers using the road because of reduced structural integrity the asphalt and road. Not to mention, heating makes asphalt roads mores susceptible to rutting and potholes.
Railways also are affected by heatwaves. Steel rails get 20 degrees hotter than the air temperature. Under intense heat, rail tracks soften and can buckle, joints can expand leading to potential derailment of trains. The overhead lines do sag under intense heat as well.
Water supply challenges and increased demand are also issues to contend with. Not only do higher temperatures cause faster evaporation of water sources like rivers, and reservoirs, they also increase demand as people use more water to stay hydrated, watering gardens, and taking more showers.
Water infrastructure such like pipes undergo more strain due to increased demand, expansion, that can lead to leaks and potential failure.
Public safety and comfort are also affected by heat waves. Outdoor workers, such as construction personal, public transportation users and vulnerable populations (older people, women and young children) are especially at risk.
Due to the nature of their work construction workers are at risk of heat strokes, exhaustion and dehydration. They are also at risks of accidents and lowered productivity that can be caused by impaired abilities. Employers have reason to implement measures that help mitigate this risk. Altering work schedules, providing training that helps workers identify signs of heat stress, for example are some measures that can be taken.
Public transportation users can feel discomfort, increased travel times due to delays. Those in lower economic brackets, the disabled, older population can be disproportionately affected.
And lastly, long-term sustainability is an issue to contend with. The effect of heat waves on building materials, urban planning and climate resilience requirements continue to be pressing issues. Some major initiatives have outlined plans to reduce emissions that stem from the ‘operational’ side, like heating, cooling and lighting. However, solutions related to ‘embodied’ carbon emissions that stem from design, production, and deployment of material such as cement, steel, and aluminum have lagged.
Civil engineers must come up with better responses to heat waves. Common and somewhat easily implementable solutions include urban cooling strategies, such as cool roofs and pavements that are reflective and reduce surface heat. Green Infrastructure that included green roofs, urban forests, and vertical gardens can be used. The use of Heat-Resilient Materials is also an effective solution. Examples include; asphalt mixes resistant to rutting at high temperatures, heat-reflective concrete and advanced sealants.
By considering effective design of buildings and infrastructure before construction, civil engineers can become better equipped to deal with its effects not only people but also built environments. For example, Passive Cooling Designs can be implemented. Buildings can be oriented relative to the direction of a heat source in a manner that would minimize heat exposure to pedestrians and resident, ensure adequate shading. Design for cross-ventilation and thermal usage.
Another effective strategy pertains to the design of climate-resilient infrastructure. An example, transit stops can be designed to include extra shading, and brides can be retrofitted to accommodate the expansion of rail tracks and expansion joints.
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The implementation of the right technology and data in construction projects is another step in the right direction. Civil engineers should include predictive modeling of infrastructure. Predictive models help determine the demands placed on electricity grids during heat waves and help us a prepare for blackouts. Predictive modeling can also predict how road surfaces, railway tracks, and bridge expansion joints respond to heat, allowing for timely maintenance and repairs.
A few larger scale projects and adaptations in response to heat waves have already been implemented around the world. The first being Singapore’s greenery and reflective building policies. Under its Singapore Green Building Masterplan (SGBMP), a key component of Singapore Green Plan 2030, the country aims to make 80 percent of its building green by the year 2030. There are several key components of this program, including achieving a Green Mark Certification for its buildings. What this means is that its buildings must be energy efficient and have high indoor air quality, among other criteria. Singapore is also using incentives to drive this change. These include having buildings certain sizes meet minimum set environmental standards, its ‘Skyrise Greenery Incentives’
A second example is the ‘Los Angeles Cool Pavement Program’, in which a special type of coating was applied on pavement to help it cool down temperatures in neighborhoods which have low tree cover for shade. In 2022, for example, Pacoima, a neighborhood in Los Angeles was covered in over 700,000 square feet of reflective pavement coating. How effective is it? It uses gray coating, which overall surface temperatures by as much as 10 degrees Fahrenheit cooler. This type of pavement coating used, reflects sunlight. Although natural shade is still more effective than this method, it is an apt alternative for areas where it would be difficult to implement natural vegetation that offers shade.
Seville, one of the hottest places in Europe implemented its own urban shade project as means to combat extreme heat. This has included the use of water misting systems, greenery, awnings and shade structures such as Setas de Sevilla, a large wooden structure in Plaza de la Encarnación which provides shade and incorporates a market, restaurants, and other public spaces. Certain public places have hidden water jets that emit fine mist into the air. Seville has also promoted the reduction of asphalt surfaces and using instead light permeable materials to reduce the use of heats islands.
These projects and iniatives aim to improve comfort and livability, especially during the scorching summer months.
Effective use of policy and collaboration is another area civil engineers can use to combat heat waves. This can entail influencing zoning and building codes, partnering with environmental scientists and public health officals and raising public awareness campaigns on heat safety.
As global warming continues to become a major issue, civil engineers must continue to have a proactive rather than a reactive approach to the problem of heat waves.
Because of the nature of current urban design and the fact that construction material often absorb heat other than reflect it, and the synergistic relation between heat waves and UHIs, construction of projects must be designed to include frontline defenses that help cities adapt to this kind of pressure. Design must be innovative and resilient in nature.
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