7/24/2017 Urban Heat And Urban Design — An Opportunity To Transform In NYC | Joyce Klein-Rosenthal + Jeffrey Raven | Snapshot Column | the Sallan… https://www.sallan.org/Snapshot/2017/07/urban_heat_and_urban_design_an_opportunity_to_transform_in_nyc.php#.WXZfLYjyvD4 1/8 Snapshot Snapshot Table of Contents: (http://www.sallan.org/Snapshot/) « How Passive Houses Took Over Brussels (http://www.sallan.org/Snapshot/2017/05/how_passive_houses_took_over_brussels.php) | SNAPSHOT Urban Heat And Urban Design — An Opportunity To Transform In NYC By: Joyce Klein-Rosenthal + Jeffrey Raven July 18, 2017 How can planners and designers work with large urban centers to prepare for the adverse impacts of climate change, while also adapting to current climate variability and extreme weather events? With a substantial expected increase in daily average temperatures in coming years, mid-latitude cities such as New York are also expected to experience more frequent and intense heat waves (NYCPCC, 2015; USGCRP, 2016). Part 1 of this article describes the urban climate phenomenon that amplifies the harmful effects of urban heat — the urban heat island (UHI) effect — and presents concepts for adaptive urban design strategies to improve the urban environment and mitigate the UHI effect, as the first of a two-part discussion. Part 2 (to be posted in August 2017), will describe an important case study now in the works; NYC's rezoning of the East Midtown (https://www1.nyc.gov/site/planning/plans/greater-east-midtown/greater-east- midtown.page) business district in Manhattan, and how that dense core district may be redeveloped to respond and adapt to climate risks. The redevelopment of East Midtown (EM) provides an opportunity for urban designers and planners to consider climate-informed guidelines for land-use development in New York City, by applying the best practices of adaptive design during the initial planning stages of redevelopment, to transform the city's built environment, reduce the urban heat island effect, while creating the framework for a healthier and more sustainable central business district. Designing for uncertainty — Climate risk and the urban heat island effect Confronting the challenges of climate change in global cities requires expanding the agency of urban planning and design within urban development, and the integration and application of knowledge of climate science and ecology to the planning and design of climate-resilient communities. Applying knowledge of urban climate to design dynamic, desirable and healthy communities begins with an understanding of climate risk, within an embedded understanding of the political, economic, social, health and ecological priorities of community residents. The problem: Hot days and nights in the urban heat island The urban heat island effect refers to the higher temperatures that can be found in city centers, which makes them hotter than their surrounding suburban and rural areas, due to their human-made surfaces, lack of vegetation, and lack of natural land-cover. Heat islands are created principally by human-made surfaces, including asphalt or concrete roofs, parking lots and roads, which absorb sunlight and re-radiate that energy as heat. The concrete, metal and stone of buildings and street surfaces store and conduct heat, and act as multiple reflectors of this energy (Clarke, 1972). Since city streets typically have fewer trees and vegetation to shade buildings and cool the air by evapotranspiration, urbanized land-cover tends to retain less surface water from precipitation than natural land-cover, and moisture is less available for evaporative cooling (Hart & Sailor, 2009). Urban areas generally have lower wind speeds, and less building heat is lost to the atmosphere by convection (Clarke, 1972) due to the reduced sky-view factor. Other factors that contribute to warmer urban streets include: increased storage of heat by urban materials; city morphology, urban design, such as the orientation and form of buildings and roads; building massing; the creation of anthropogenic heat; the relative lack of water in urban environments; and lower heat loss and altered wind patterns in narrow urban canyons (Chow & Roth, 2006; Hough, 2000). Synoptic weather conditions such as wind speed, cloud cover and height, can enhance the magnitude of the heat island effect (Oke, 1973; Gedzelman et al., 2003). Additional anthropogenic sources of heat, such as air-conditioning systems that dump waste heat outside of buildings, add heat to the pedestrian environment during the hottest times of the year. Lower surface albedo, a measure of reflectivity, results in greater absorption of incoming solar radiation. Policy makers and planners must be alert to UHI magnitude; this is the temperature difference between a city and its surrounding region, which is greatest during dry, clear, low-wind nights, as the surfaces that comprise the built environment retain and re-radiate more heat into the air at night than vegetation and non-urban land (Clarke, 1972; Gaffin et al., 2008). This is a problem for public health, as those without air conditioning at home can suffer from continued exposure to very hot temperatures at night. The surface geometry and thermal properties of the built environment significantly impact the heat island magnitude (Voogt, 2002). Building