Urban heat islands are a clear, well‐documented example of an anthropogenic modification to climate that has an atmospheric, biological, and economic impact. This review shows how field‐based and modeling studies continue to help unravel the factors that are responsible for heat island development and are providing a basis for the development and application of sustainable adaptation strategies. As urban areas continue to expand, there is a heightened awareness that scientific knowledge of the urban heat island must be more effectively communicated to architects, engineers, and planners and translated into intelligent urban design. Green roof technology is a case in point. This and other technologies are being slowly adopted, and research published since 2003 suggests that the pace with which many practical applications are put into practice should accelerate.

Cities artificially alter local climates affecting economic and biological processes. This study examined air temperatures in Orlando's urban canopy layer using a network of twenty-nine fixed-point stations from September ∞ΩΩΩ to December ≤≠≠∞. Urban Heat Island (UHI) statistics were calculated using two stations that were representative of an urban and rural setting. Orlando's UHI develops best on calm, clear nights during dry months: its maximum magnitude exceeds ∫\C. Orlando's UHI, however, is predominantly a nocturnal phenomenon with intense heat islands sometimes occurring during warm afternoons. These events are most likely attributable to isolated thundershowers. Local temperature variations between urban and rural extremes were examined by calculating environmental indices for all stations. The range in monthly cooling degreeday totals exceeded ∞≠≠ degree days in six months of the thirty-six month study period. Heating degree totals and number of freezing hours were also highly variable. key words: urban climate, urban heat island, temperature variability, Orlandointroduction Urban climates differ significantly from conditions in the surrounding region. The higher evening and early morning temperatures of cities, commonly called the urban heat island (UHI) effect, results from differences in thermal and physical properties of construction materials, building geometry, surface roughness, factors contributing to decreased evapotranspiration, and anthropogenic heat sources (Tyson, Garstang, and Emmitt ∞Ωπ≥; Oke ∞Ω∫π). Urban heat islands have been studied in numerous cities around the world because the myriad factors leading to the existence of an UHI differ from city to city. It is important to understand heat islands in many cities to detect the impact artificially elevated temperatures have on human comfort (Palecki, Changnon, and Kunkel ≤≠≠∞), city water and energy demand (Balling and Brazel ∞Ω∫∫; Jauregui ∞ΩΩ∫; Palecki, Changnon, and Kunkel ≤≠≠∞), air pollution (Viras ≤≠≠≤), and the introduction of bias into long-term temperature records (

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Urban climates have existed ever since the first human settlements altered the natural environment thousands of years ago. During the first century ce, Pliny the Elder recorded anecdotal accounts about the differences between the air in ancient Rome and the air in rural surroundings. Urban development accompanied global population growth over the following centuries. Today, well over half of the world’s population lives in cities and that proportion is increasing. All urban inhabitants experience a local climate that is somewhat different from that in surrounding rural areas. That, coupled with increasing challenges presented by large-scale climate change, necessitates research to understand how the unique climates caused by urbanization behave, how they impact the residents who live there, and what can and should be done to address ill-effects equitably. The first formal scientific assessment of urban climate was published by Luke Howard almost two hundred years ago in 1833. Over time, urban climatology and meteorology have blossomed into rich fields encompassing studies of a range of modified climate effects including energy balance, roughness length, turbulence and wind, atmospheric moisture, and air quality. The focus of this review is the urban heat island (UHI) effect. The UHI is generally defined as higher temperatures in urban areas compared to rural areas, which is a common feature in most cities worldwide. The first section of this review lists a select number of publications and websites that provide a sound foundation to help those new to urban climate studies become acclimated to the field. The next section delves deeper into the definition of exactly what the UHI is and how it is observed. In particular, a distinction is made between UHIs in the canopy layer (usually measured 2m above the surface) and surface UHIs (measured using thermal imagery). The second section explores the impacts on human and natural systems caused by the UHI. This includes subsections about urban effects on long-term temperature records and human comfort, health, and mortality. The next section takes a look at the various methods used to limit the adverse effects of the UHI. Ideas ranging from green and blue strategies to advanced building materials are discussed. The last part of this review concerns environmental justice. Many of the people who face the direst of unintended consequences caused by urbanization are those who are least well equipped to handle the additional pressures.

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