Regardless of how extensive climate change mitigation efforts are in the near future, many climate experts argue that some degree of adaptation to climate change is required in order to handle the worst anticipated effects. Human and natural systems must become more resilient to expected changes. In fact, the smartest communities are using the threat of climate change to invest in long-term environmental, economic, and social sustainability while protecting their infrastructural assets and housing stock.
With expected temperature increases along with more temperature fluctuations, Washington, D.C., like many other cities in the U.S. and Europe can pre-emptively adapt by adding additional street and park trees to moderate air temperatures. Washington, D.C., leadership should evaluate whether its goal of 40 percent tree canopy by 2035 will be sufficient to achieve the required adaptation benefits.
According to the U.S. EPA, trees provide evaporative cooling through their leaves, which increases air humidity. Shaded surfaces can be 20-45 degrees cooler, and evapotranspiration can reduce peak summer temperatures by 2-9 degrees. Cooler air is important because many urban air quality issues are only further exacerbated by higher air temperatures.
Washington, D.C., should pre-emptively adapt by adding more shade trees to streets and parks, particularly in neighborhoods with vulnerable populations.
Furthermore, a green roof project organized by Columbia University and New York power company Con Edison adds to a growing body of research that demonstrates green roofs reduce the urban heat island effect. Using Con Edison’s training center in Long Island City, Queens, the researchers found that a layer of roof-friendly soils and plants reduce the rate of heat absorption by 84 percent in the summer. In addition, a study cited by The Guardian (UK) noted that even simple efforts such as painting roofs white, or even light grey can have significant positive impacts. “Computer simulations of Los Angeles show that resurfacing about two-thirds of roads and rooftops with reflective surfaces, as well as planting more trees, could cool the city by 2-3C.” Cooler cities also mean less energy use for air conditioning.
D.C. should follow Toronto’s lead and mandate the use of green roofs in all new buildings. To address older structures, the District can follow Philadelphia’s approach and introduce a stormwater runoff fine, which will incentivize the use of green roofs, bioswales, and permeable pavements – systems that not only cool but also store stormwater. The city can also incentivize the use of green roofs in older buildings by providing tax breaks for feasibility studies and other preliminary design assessment costs. Lastly, white roofs can also be incentivized, if combined with green roof systems, or if the building structure can’t handle a green roof.
Kristina Hill, Ph.D., Affiliate ASLA, chair of the landscape architecture department at the University of Virginia, and a leading thinker on wildlife and climate change adaptation, argues that communities must begin to think seriously about the impacts of climate change on local plant and animal species, outlining some expected impacts on ecosystems:
“If species characteristic of a region start to die out, will species that could survive the new seasonal conditions be able to get there, find suitable locations, and successfully reproduce before they die out in their own regions? When will the species that are their food be available locally? When will new predators, parasites, and competitors also move in? It’s a very complicated four-dimensional chess game. That’s why no one can really predict which species will survive where.”
Washington, D.C., can use its parks and man-made landscapes to contribute to the overall ability of the region to sustain plant and animal species by focusing on preserving cooler zones. Hill explains one strategy being developed: “The potential new spatial strategy in all this involves conserving slopes with northern aspects, linking them to each other via waterways and ridges. These slopes can be potential refuges for biodiversity in an era of increasing temperature spikes and drought events. Like the cove forests of Appalachia, these cooler, protected areas will be places where the species that have been characteristic of many regions may persist as climate change occurs – making them key elements of future habitat diversity and possibly trait diversity.”
Washington, D.C., should undertake a review of its green spaces and infrastructure and develop a comprehensive plan covering how plant and animal species can be preserved, protected, and re-introduced. Dedicated wildlife corridors should be established. Plant lists should be updated to reflect changes in climate. Just as Chicago has done, there should be a new set of “recommended trees” better suited to handle heat and drought conditions.
In an era of rising temperatures, water efficiency will be increasingly important. Washington, D.C., should develop more stringent rules that require commercial owner and homeowners to use drought-tolerant appropriate (native and adapted) plant species, and develop systems that infiltrate, store, and recycle water, limiting the use of valuable potable water for landscapes. Residential systems such as green roofs, bioswales / bioretention ponds, rainwater gardens, and water recycling and drip irrigation can all be used to efficiently conserve water. Commercial owners and homeowners should be allowed to use “Living Machines,” or constructed wetlands, which are systems that recycle and reuse greywater (and even blackwater) for landscape maintenance and other safe re-uses like toilet-flushing and car-washing.
Separately, Washington, D.C., should also ensure all parks and public green spaces meet the highest standards of water efficiency. This can be achieved in part by requiring parks and public green spaces to use appropriate (native and adapted) plants. The Sustainable Sites Initiative (SITES) presents a model for achieving these goals. New York City and other cities have also created local guidelines. Washington, D.C., should also use its own parks to undertake a broad public education campaign about water efficiency in the city.
Washington, D.C,. should incentivize water efficiency measures by requiring the use of drought-tolerant appropriate (native and adapted) plant species in public and residential landscapes, and enabling filtered or treated greywater (and even blackwater) reuse for landscape irrigation. As part of a public education campaign, parks and public green spaces should follow the highest water efficiency standards.
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