Cooling Albuquerque, New Mexico, with Green Roofs

A city does what it has to in order to be sure its citizens can stay safe and protected in the midst of so many dangerous events like crime and murder. One dangerous outcome may come traditionally undetected and that is deaths related to heat waves. San Francisco did all that it could to protect against such a disastrous attack like setting up shelters with air condition, making swimming pools open and free to the public, and opening four air conditioned libraries. This was not enough. Over the Labor Day weekend heat wave of 2017, where temperatures reached triple digits, three elderly people, all in their late 70s to early 90s, died due to the heat wave (Swan, 2017). In San Mateo county in California, just outside of San Francisco, the coroner said three more elderly people died from shock because of the heat wave over the same Labor Day weekend. (Rocha, 2017). The Intergovernmental Panel on Climate Change agrees that heat waves are more likely to be more intense in cities due to the already high temperatures from the Urban Heat Island effect. (IPCC AR5, 2014, p.7-8). This exacerbates the conditions usually seen in heat waves, so not only do cities experience higher temperatures, but also more deaths related to these rising temperatures. Only three names were made public, but like the deaths of Patrick Henry, 90, Ernesto Demesa, 79, and Loraine Christiansen, 95, all of San Mateo county, more elderly are at risk during these heat waves compared to the rest of the population. (Rocha, 2017). Green roofs can help alleviate rising temperatures and urban heat island effect in cities.

Cities, on average, are affected more by heat waves than surrounding areas due to the urban heat island effect. The Urban Heat Island (UHI) effect is the heating of urban areas, typically cities, due to the design and material choice of urban architecture and the high volume of emissions emitted from transportation, which it then trapped in the urban environment. (Monteiro et al., 2017). A city like Albuquerque, New Mexico has experienced temperature differences of up to 22°F between the city and the surrounding rural areas on an average summer’s day, Albuquerque is number two in the United States for the greatest difference in temperature between city and rural communities (Hot and Getting Hotter, 2014). Temperatures inside the city have reached up to 100°F five times in 2016 alone, and the hottest day on record in Albuquerque was 107°F on June 26, 1994 (US Department of Commerce, 2016 ). This increase in temperature causes fatal living conditions. (Monteiro et al., 2017).

Rising temperatures from UHI has also been known to cause heat exhaustion, heat cramps, non-fatal heat stroke, respiratory issues and even heat-related mortality (United States Environmental Protection Agency [EPA], 2017). These results are more likely to affect sensitive populations like young children and older adults, like those in San Mateo county. (EPA, 2017).

Cities have little to no vegetation. Vegetation promotes evapotranspiration which can help reduce temperatures by 2° F to 9°F (EPA, 2017). The effects presented by decreased reflectivity, increased heat retention, and lower evapotranspiration is like wearing a black wool sweater on a hot July day in the desert. If you wear a black wool sweater in the middle of the summer, your sweat is going to be trapped in the sweater, and prevent evaporation, unlike a moisture wicking white t-shirt which allows your sweat to evaporate off of you and carry away the heat. One way to think of this in effect is also the way that humid air feels warmer, because your sweat won’t evaporate, whereas dry heat feels cooler because of its ability to absorb moisture and allow evaporative cooling.

The white t-shirt will also be able to reflect more sunlight due to its lighter color compared to the black sweater. Green roofs are the white cotton t-shirt, a good solution to feeling hot while succumbing to the conditions of the black wool sweater as the urban heat island effect. In order to mitigate some of the UHI effects in Albuquerque, New Mexico, the New Mexican government must create incentive programs to help encourage the design and development of green roofs.

A large factor contributing to UHI is the reduced albedo caused by dark surfaces, used on roads and roofs, decreasing reflectivity and increasing heat retention. (Morini, Touchaei, Rossi, Cotana, & Akbari, 2017). Albedo is a measure for how well a surface reflects light without absorbing it in the form of heat (Morini et. al, 2017). Urban architecture plays a big role here. Since pavements and roofs typically constitute over 60% of urban surfaces, increasing reflectivity will drastically increase albedo and decrease UHI (Akbari, Menon & Rosenfeld, 2009). Decreased albedo, or decreased reflectivity, has been known to raise the temperatures of exposed urban surfaces, like rooftops and pavement, to temperatures 50°F to 90°F warmer than ambient air temperatures, whereas shaded surfaces, or rural surroundings, remain closer to air temperatures (EPA, 2017). Because rural areas do not have such an abundance of these dark materials, rural areas are 18°F to 27°F cooler during the day than nearby cities (EPA, 2017).

There is a cycle that begins when UHI occurs in a city. UHI causes an increase in air temperatures and leads to uncomfortable living conditions, that is then countered with an increase in air conditioning. Warmer environments lead to more air conditioning and energy use, therefore UHI will cause an increase in energy use through an increase in air conditioning. Research shows that there is a 1.5 – 2.0% increase in electricity demand for every 1°F increase (EPA, 2017)

An increase in energy demand due to UHI effects will require power plants to produce more energy which will emit greenhouse gases into the atmosphere and add to the already pressing issue of climate change. CO2 is the most prominent greenhouse gas and is primarily caused by the burning of fuel in order to produce energy (EPA, 2017). With multiple days reaching temperatures over 100°F in Albuquerque, UHI and its effects result in huge spikes of energy consumption. Greenhouse gasses trap heat in the atmosphere and increase temperatures (The Greenhouse Effect, 2017). Because of the effects of UHI, power plants will need to produce more energy to meet the demand and emit additional CO2 into the atmosphere in the process. This increase in CO2 will contribute to climate change in the form of a greenhouse gas. All of these causes lead to the urban environment experiencing greater temperatures than before, which brings the cycle back to the issue of having to increase air conditioning usage, it is a perpetual cycle that is harming the environment by contributing to climate change and heating up the urban environment.

The IPCC states that climate change is real and is increasing temperatures at an unprecedented rate. They are “virtually certain” that there will be more hot and fewer cold temperature extremes over as temperatures continue to increase. This rise in temperatures has a direct effect on UHI and heat waves. The Fifth Report put out by the IPCC states that it is very likely that heat waves will occur more often and last longer than previous years and that it is very likely the cause of human activities like burning fossil fuels. (IPCC AR5, 2014, p. 7-8).

Given that this cycle caused by human activity it only seems fit that there should be an initiative taken to break the cycle. The cycle begins with urban architecture increasing the temperatures of an urban environment and inside of buildings, and by using green roofs we can reduce the temperature of both the urban environment and inside of buildings. Green roofs reduce the effects of UHI through its high reflectivity and its ability of evapotranspiration.

A green roof’s reflectivity has drastic effects on the temperature of the outdoor air when compared to a traditional roof. During a normal sunny day, a green roof’s increased reflectivity can cause the temperature of the roof top surface to be cooler than the temperature of the air, as opposed to a traditional roof in which the surface temperatures can be upwards of 104°F warmer than the air (William et al., 2016). By increasing the solar reflectivity of a roof top, the outdoor air temperature will be lower, and will reduce the demand for air conditioning.

Another way that greater reflectivity reduces energy requirements of a building is by reducing the through roof heat gain (TRHG). TRHG flux is higher for roofs with a lower solar reflectivity, regardless of the region (Kibria, O’Brien, Alvey, & Woo, 2016). By increasing the reflectivity of a roof the indoor air temperatures will be lower too, by preventing heat from entering a building through the roof. Reflectivity has two benefits, both lowering the outdoor air temperature of the urban environment and the indoor air temperature of a building.

Green roofs will reduce energy demands by decreasing a building’s ability to absorb heat. Green roofs cause a cooling effect called evapotranspiration. This sensation is essentially to a building like sweating is to a human, the water on the green roof evaporates into the atmosphere and carries away its embodied heat. By having plants on a roof, the water they use and obtain will absorb heat that would have been absorbed into the building. The water then evaporates, reducing the amount of heat that could have potentially been absorbed into the rooftop and into the building. Less heat is absorbed by the rooftop and transferred to the building (William et al., 2016).

Although there are benefits to green roofs some are opposed to them due to the higher upfront cost and higher maintenance cost. The cost per square foot ranges from $10 to $25 and the annual maintenance of green roofs is $0.21 up to $1.50 per square foot (EPA, 2017). These figures are dependent on the types of plants, the media, and the extent of maintenance and irrigation.

This in turns forces a lot of pressure on the owners to absorb this cost of installation and also puts pressure to maintain them as well. In Southern California, if only half of the roofs are green, then $211 million will be saved in heating and cooling cost in the long run (Garrison, Horowitz 2012). In a University of Michigan study, a 21,000 square foot green roof would cost $464,000 to install versus $335,000 for a regular roof. The study also says that the green roof would save up to $200,000 in reduced energy costs (U.S. Environmental Protection Agency, 2008). With green roofs having multiple benefits and the upfront cost being minimal compared to the savings, it seems reasonable to have this cost be a part of buildings plan.

In order to mitigate the negative impacts of urban heat island in Albuquerque, the city must provide an incentive program for green roofs for new buildings. An incentive program would encourage developers by educating them on the benefits of green roofs and by covering a portion of installation cost. There are a number of places in the world that have recognized the many benefits of green roofs and adopted them into their urban development programs. Canada has been one of the leading countries in North America when it comes to green infrastructure legislation, especially in Toronto, Ontario where green roof programs have been implemented since 2006. (City of Toronto, 2017).

In 2006 Toronto, Ontario initiated the Green Roof Incentive Pilot Program to promote the design and development of green roofs on privately owned commercial/ industrial buildings. After one year the program was deemed “very successful” by the city and had awarded 16 applications with grants resulting in over 32,290 square feet of green roofs on new buildings (City of Toronto, 2017). After receiving feedback from the applicants about the pilot program it was determined that although it was successful, they could attract more applicants by increasing the incentive to $5 to square foot which was average for similar incentive programs in the country. (Gironimo, 2007). Within 5 years it was reported by the program coordinator that this program supported a total of 112 projects with a total of 2,507,991 square feet, reducing energy consumption by an estimated 565 MWh, avoiding 106 tons of greenhouse gases (Baynton, 2015, para. 3).

In order to be eligible for this grant the developer must have provided documentation of a design and maintenance plan for the green roof of a new building. This program did not offer grants for developers retrofitting green roofs due to the variables with the type of roofing materials and the amount of weight the building was designed to support. Minimum coverage requirements ranging from 20% for small roofs and up to 60% for larger roof tops were also put into effect. Although larger roofs require 60% of coverage there was a cap of $100,000 for the grant (City of Toronto, 2017). This program is in use today in Toronto and is now a key part of their Climate Change Action Plan and is complimented by the Green Roof Bylaw where the installation of eco-roofs is mandatory for new buildings.

Since this program has shown to be successful over a long period of time according to the city of Toronto, this same sort of incentivized program would be viable for Albuquerque. This program would also provide grants for eligible applicants at $5 per square foot for up to $100,000 for new industrial and commercial buildings and have the same eligibility requirements. With a $5 per square foot incentive, this would cover 20%-50% of installation cost on an average greenhouse relieving pressure from the developers. In order for this plan to work, builders must be educated on the number of benefits for this system by providing resources like pamphlets, websites, and seminars in order to communicate the value of these systems and how the long term benefits outweigh the initial costs.

In order to break the UHI cycle and the rapid increase in temperatures in Albuquerque there must be an incentive program run by the city or state government. Government officials need to address this issue since it impacts the health and well-being of its inhabitants. The impacts on health have led to death and other health complications and with temperature continuing to rise, it seems reasonable to assume the amount of deaths, complications, and general discomfort will rise too. In order for people to alleviate themselves from high temperatures, they must turn to cooling technology. Rising temperatures means that buildings must increase the amount of fossil fuels used to cool buildings which increases not only the cost of cooling, but the amount of greenhouse gases, in this case CO2, in the atmosphere. Greenhouse gases then go on to contribute to rising temperatures in cities which then continues the cycle.

Green roofs can help to break this cycle by helping to reduce the amount of heat trapped in these urban areas by increasing evapotranspiration and reflectivity. By increasing these two properties, less heat is retained in the buildings which then decreases the amount of fossil fuels used to cool buildings and reducing the amount of greenhouse gases in the air.  By implementing an incentive policy that educates and encourages developers to install green roofs, the impacts of UHI will decrease. Unless the New Mexico government steps in, like Toronto, and provide incentives to green roof installation the cycle could continue on indefinitely affecting more families like those in San Francisco.

AUTHORS

Evan Brillhart – Natural Resource Conservation

Jacqueline Dias – Environmental Science

Michael Pfau – Building and Construction Technologies

Amanda Tessier – Horticultural Science

REFERENCES

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Evan

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