Austin is one of America’s fastest-growing cities. This growth has brought dynamism to the city, but has also created environmental problems. Because much of Austin’s growth has taken place at the urban fringe, the addition of new residents and businesses has caused persistent and worsening problems with traffic congestion, air pollution and water quality, as more undeveloped land is converted into new development.
To accommodate the continued influx of new people to the city, Austin is currently revising its land development code in a process called CodeNEXT. This revision seeks to house a growing population in ways that minimize the increase of developed land.
Compact development can deliver tangible benefits for the environment – reducing energy use and greenhouse gas emissions, curbing the flow of polluted runoff into streams and lakes, and protecting natural areas and agricultural lands. By adopting strong policies to mitigate the local impacts of greater density, such as green infrastructure to manage stormwater, Austin can develop in a way that will bring lasting environmental benefits.
Compact development benefits the environment in numerous ways.
- Energy use and greenhouse gas emissions: Compact development uses less energy for construction, building operation and transportation, which results in lower greenhouse gas emissions.
- In Austin, a suburban neighborhood with detached single-family homes can consume up to three times more energy in construction and materials, and up to 50 percent more energy in daily operation than a densely developed neighborhood with duplexes and low-rise apartments.
- Shared walls in attached buildings result in direct energy savings as housing units share and save heat, with less leakage.
- Energy used for transportation currently generates 35 percent of greenhouse gas emissions in Travis County. The 2007 study Growing Cooler and other studies have found that people living in compact neighborhoods drive 20 to 40 percent less than those living in sprawling neighborhoods, using less energy and producing fewer emissions.
- Water quality:Compact development reduces land conversion, which has a significant impact on water pollution. Compact development also produces less runoff and affects less of a given watershed than lower-density development, resulting in healthier waterways and aquifers for the same amount of housing capacity.
- A Houston-area study suggests that doubling density in that city would result in less overall pollution in the area’s bays and bayous, and would do more to curb pollution than many traditional tools for managing stormwater.
- Urban sprawl also affects aquifer recharge. The amount of clean rainwater that can infiltrate into the soil where it falls is reduced by sprawl, while the amount of dirty runoff polluted with pesticides and pathogens is increased. This can result in poor water quality in some areas where polluted water enters Austin’s waterways, threatening surface and groundwater quality.
- Flood risk:Compact urban development can help minimize the total amount of paved land in the metropolitan area, which contributes to less total runoff and reduced flood risks.
- The U.S. Geological Survey studied 25 years of streamflow and rainfall data along Waller Creek and found that converting land along the creek for development increased the scale and frequency of flooding.
- A 2003 study published in the Journal of Water Resources and Planning found that high- and medium-density development increased impervious cover 72 percent less than low-density development. As a result, high- and medium-density developments had less than half the effect of low-density development on runoff volume and peak flow.
- Water consumption: Compact development can result in lower water use than sprawling development. Building more compactly on smaller lots can decrease water demand for landscaping and minimize overall water demand.
- A 2007 study found that water use in single-family units in the Phoenix metro area increased by 1.8 percent for each 1,000-square foot increase in average lot size, and by 1.7 percent for every 1°F rise in the average daily temperature low due to the urban heat island.
- In Austin, outdoor uses, like residential lawn watering and commercial landscape irrigation, account for more than a fifth of total water use, with a summertime peak. Austin also has the highest percentage of big-lot homes among the four major metro areas of Texas, with 6.6 percent of single-family homes on 5-acre lots or more. Smaller lot sizes could help to lower water demand and reduce pressure on Austin’s water resources.
- Land consumption: Population growth, suburbanization and urban development drive land conversion in Texas.
- The Texas A&M Institute of Renewable Natural Resources estimates that between 1997 and 2012, Texas lost more than 1.1 million acres of farms, ranches and forests to urban and suburban development, 87 percent of which lie within the state’s 25 fastest-growing counties.
- Air quality: Compact development forms can reduce traffic over a metropolitan area, which results in lower levels of ozone, a ground-level pollutant that can cause adverse health effects.Compact development can also reduce urban heat island effects, which contribute to ozone pollution; as a result, compact cities have relatively fewer heat waves, and improved regional air quality.
- Sprawling cities have been found to experience up to 62 percent more high ozone days than compact cities.
- Particulate pollution causes approximately 8,700 premature deaths in Texas each year, and ozone pollution causes approximately 2,100 more.
Compact forms of development deliver environmental benefits at the regional level, but may create local environmental and public health impacts. Through smart public policy, Austin can mitigate many of the local impacts of compact development.
- Green stormwater infrastructure (GSI) can help compensate for the increase of impervious cover in densely developed areas. By using natural drainage processes to capture and cleanse rainwater on-site, GSI features can reduce water pollution and flooding severity. GSI features are especially effective at filtering surface pollutants out of stormwater, and can generally retain enough water to reduce or even eliminate flooding from small to mid-size storms.
- Limiting the overall amount of impervious cover helps ensure the preservation of undeveloped land where rainwater may naturally infiltrate the soil or be stored, which enhances flood resiliency. But impervious cover limits, like the Save Our Springs Ordinance that limits impervious surface to 15 percent of the total site area in the Barton Springs Zones, must be implemented with care to ensure that they do not increase incentives for sprawl.
- The localized increases in vehicular traffic and air pollution that may result from increased density can be reduced through improvements in public transportation, vehicle electrification, mobility as a service (e.g, ride-hailing), and improved infrastructure for walking and biking. Today, Austin ranks only 21st in job accessibility via transit out of the 50 metro areas with the largest populations. Compact, mixed-use neighborhoods built around high-capacity transit can help decrease energy use and greenhouse gas emissions.
- Street and building designs that maximize vegetation and reflectivity can reduce urban heat island effects. One study focused on development in Houston found that placing shade trees near buildings and using light-colored roofing and paving materials that reflect sunlight could save $82 million on energy, decrease peak power demand, and cut carbon emissions by an amount equivalent to taking more than 199,000 passenger vehicles off the road.
The current revision of Austin’s land development code, last overhauled in the 1980s, gives the city a golden opportunity to reshape how it develops for coming generations. Expanding the areas within Austin where compact and walkable neighborhoods can be built would reduce the pressure for further sprawl, protect our environment, and enhance our quality of life. Austin should adopt a new development code that increases neighborhood walkability, provides “missing middle” housing (a wide range of residential forms between single-family homes and high-rise apartment buildings), and reduces the considerable environmental damage caused by sprawl.