Urban Heat Island Magnitude Research Articles

Exploring the influence of impervious surface density and shape on urban heat islands in the northeast United States using MODIS and Landsat

Impervious surface area (ISA) from the National Land Cover Database 2001 and land surface skin temperature from MODIS averaged over three annual cycles (2003–2005) are used in a spatial analysis to assess the surface urban heat island (UHI) signature and its relationship to settlement size and shape, development intensity distribution, and land cover composition for 42 urban settlements embedded in forest biomes in the northeastern United States. Development intensity zones, based on percent ISA, are defined for each urban area emanating outward from the urban core to nearby rural areas and are used to stratify land surface temperature. The stratification is further constrained by biome type and elevation to ensure objective intercomparisons between urban zones within an urban settlement and between settlements. Stratification based on ISA allows the definition of hierarchically ordered urban zones that are consistent across urban settlements and scales. For cities within the northeastern US temperate mixed forest biome, we found that settlement size, shape, and development intensity significantly influenced the amplitude of summer daytime UHI. Our study indicates that for cities of similar size, the ISA density distribution within the urban area and the shape of the urbanized area as measured by area to perimeter ratio are significant modulators of UHI magnitude. Our results indicate that remotely sensed satellite data provide a consistent characterization of the UHI magnitude as well as its major drivers across regional scales.

Simulating climate change in UK cities using a regional climate model, HadRM3

AbstractA regional climate model (RCM) at 25 km resolution, coupled to a simple urban land‐surface scheme has been used to assess the sensitivity of UK urban climates to large‐scale greenhouse gas (GHG) induced climate change, local forcing from urban land use, and anthropogenic heat flux (AHF) resulting from energy use in urban areas. GHG‐induced climate change is similar over both urban and rural land surfaces in the model, suggesting that under a changing climate the relative magnitude of urban heat islands in the UK would remain the same. However, indirect effects from urbanisation or changes in energy consumption within UK cities would contribute to further localized anthropogenic climate change that can be quantified by this model. The presence of the urban heat island also has a significant impact on the frequency of extreme high temperatures both in present and future climates, and will exacerbate the impact of climate change on the urban population.The simple urban land‐surface exchange scheme is a cost effective additional component of the RCM. It is shown to provide a realistic city‐scale urban heat island responding to the dynamical weather of the model at every model time‐step, with a magnitude and variability comparable to observed values. The climate model provides long integrations to derive large samples of heat islands under a full range of simulated dynamical conditions, and in this study sampling more than 100 years of climate change. Copyright © 2011 Royal Meteorological Society and British Crown copyright, the Met Office

Assessment of the canopy urban heat island of a coastal arid tropical city: The case of Muscat, Oman

The spatio-temporal variability of the canopy-level urban heat island (UHI) of Muscat is examined on the basis of meteorological observations and mobile measurements during a span of 1 year. The results indicate that the peak UHI magnitude occurs from 6 to 7 hours after sunset and it is well developed in the summer season. The warm core of the UHI is located in the Highland zone of Muscat, along a narrow valley characterized by low ventilation, high business activities, multi-storied buildings and heavy road traffic. Topographically, this valley is surrounded by mountains formed of dark-colored rocks such Ophiolites that can absorb short wave radiation and contribute, herewith, to the emergence of this warm urban core. In addition, this mountainous terrain tends to isolate this location from the cooling effect of the land–sea breeze circulation during the day time. In this warm valley the hottest temperature is encountered in the compact districts of old Muscat. In comparison, the urban thermal pattern in Lowland zone of Muscat is fragmented and the urban–rural thermal difference is reduced because of the lower urban density of the residential quarters. In addition, the flat alluvial terrain on which these residential quarters are located is consistently exposed to the land breeze circulation. Also, the study illuminates and emphasizes the importance giving due consideration to the nature of the rural baseline when assessing the urban effect on an area's climate. For Muscat City, irrespective of the rural baseline used, a significant difference in the value of the urban heat island is registered.

A systematic review and scientific critique of methodology in modern urban heat island literature

AbstractIn the modern era of urban climatology, much emphasis has been placed on observing and documenting heat island magnitudes in cities around the world. Urban climate literature consequently boasts a remarkable accumulation of observational heat island studies. Through time, however, methodologists have raised concerns about the authenticity of these studies, especially regarding the measurement, definition and reporting of heat island magnitudes. This paper substantiates these concerns through a systematic review and scientific critique of heat island literature from the period 1950–2007. The review uses nine criteria of experimental design and communication to critically assess methodological quality in a sample of 190 heat island studies. Results of this assessment are discouraging: the mean quality score of the sample is just 50 percent, and nearly half of all urban heat island magnitudes reported in the sample are judged to be scientifically indefensible. Two areas of universal weakness in the literature sample arecontrolled measurementandopenness of method: one‐half of the sample studies fail to sufficiently control the confounding effects of weather, relief or time on reported ‘urban’ heat island magnitudes, and three‐quarters fail to communicate basic metadata regarding instrumentation and field site characteristics. A large proportion of observational heat island literature is therefore compromised by poor scientific practice. This paper concludes with recommendations for improving method and communication in heat island studies through better scrutiny of findings and more rigorous reporting of primary research. Copyright © 2010 Royal Meteorological Society

Study on the urban heat island effects and its relationship with surface biophysical characteristics using MODIS imageries

This study assesses surface urban heat island (UHI) and its associated surface physical characteristics using remote sensing approaches. TERRA/MODIS images acquired in 2005 in three different seasons were selected to generate land surface temperature and surface characteristics for the Changsha-Zhuzhou-Xiangtan metropolitan area in China. The intensity of urban heat island effects and its seasonal variations were examined. The result showed that UHI effects were significant both in the summer and the spring. Land surface temperatures in the city were 8°C to 10°C warmer than those in surrounding rural areas in the spring and the summer seasons. Although UHI effects exist in winter, they are not significant. Land surface temperature in the city was 4°C warmer than that in surrounding rural areas in winter. This study uses normalized difference vegetation index (NDVI) and normalized difference built-up index (NDBI) as indicators of surface physical characteristics and investigates the relationship among land surface temperature (LST), NDVI and NDBI. The results from this study indicate that, while the relationship between LST and NDVI changes in different seasons, there is a strong positive linear relationship between NDBI and LST for all seasons. The amount of slope and intercept of the linear relationship between NDBI and LST can indicate the magnitude of UHI for different seasons. This finding suggests that NDBI provides an alternative physical indicator for analyzing LST quantitatively over different seasons, and therefore providing a useful way to study UHI effects using remote sensing.

Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies

The urban heat island (UHI), together with summertime heat waves, foster's biophysical hazards such as heat stress, air pollution, and associated public health problems. Mitigation strategies such as increased vegetative cover and higher albedo surface materials have been proposed. Atlanta, Georgia, is often affected by extreme heat, and has recently been investigated to better understand its heat island and related weather modifications. The objectives of this research were to (1) characterize temporal variations in the magnitude of UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under extremely high temperature conditions during Atlanta's summer (June, July, and August) period, and (3) conduct theoretical numerical simulations to quantify the first-order effects of proposed mitigation strategies. Over the period 1984-2007, the climatological mean UHI magnitude for Atlanta-Athens and Athens-Monticello was 1.31 and 1.71� C, respectively. There were statistically significant minimum temperature trends of 0.70� C per decade at Athens and -1.79� C per decade at Monticello while Atlanta's minimum temperature remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and may be coupled to cloud-radiative cycles. Heat waves in Atlanta occurred during 50% of the years spanning 1984-2007 and were exclusively summertime phenomena. The mean number of heat wave events in Atlanta during a given heat wave year was 1.83. On average, Atlanta heat waves lasted 14.18 days, although there was quite a bit of variability (standard deviation of 9.89). The mean maximum temperature during Atlanta's heat waves was 35.85� C. The Atlanta-Athens UHI was not statistically larger during a heat wave although the Atlanta-Monticello UHI was. Model simulations captured daytime and nocturnal UHIs under heat wave conditions. Sensitivity results suggested that a 100% increase in Atlanta's surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature. However, from a mitigation and technological standpoint, there is low feasibility of tripling

Remote sensing evaluation of urban heat island and its spatial pattern of the Shanghai metropolitan area, China

With the aid of an integrated GIS/RS-based approach, methods including spatial autocorrelation, semivariance, and fractal analysis were used to quantitatively characterize the patterns of recent urban heat island (UHI) in the Shanghai metropolitan area during 1997 and 2004. Results show that newly emerging bare lands along the coastal areas and on the remote islands were well vegetated or developed for fishery, and therefore had the significant cooling effect. However, with the rapid expansion of the urbanized and urbaning landscapes, the heating effect of impervious surfaces increased in proportion. Spatial scales showed that the average size of homogeneous patches dominated with the urbanized and urbanizing areas increased remarkably, so did the extent and magnitude of hot spots. Given the growing extent and magnitude of UHI on two dates, dramatic land use and cover change in urban fringes and the major satellite towns significantly exacerbated the UHI effect on regional scale. As a whole, both the extent and magnitude of UHI in Shanghai have undergone a significant increase. Further, the patterns of UHI (as indicated by LSTs) implied the existence of spatial correlation on the small and meso scales. A directional analysis of the Hausdorff–Besicovitch dimension showed that in E–S profile of the city, the spatial dependency of UHI was mainly associated with structural variance. Relatively weak spatial dependency associated with structural variance also existed in the direction of NE–SW. As computed, the structural variation accounted for approximately 50% of the total variation. Therefore, random factors also played the significant role in causing the complexity in patterns of UHI.

Desert heat island study in winter by mobile transect and remote sensing techniques

A familiar problem in urban environments is the urban heat island (UHI), which potentially increases air conditioning demands, raise pollution levels, and could modify precipitation patterns. The magnitude and pattern of UHI effects have been major concerns of a lot of urban environment studies. Typically, research on UHI magnitudes in arid regions (such as Phoenix, AZ, USA) focuses on summer. UHI magnitudes in Phoenix (more than three million population) attain values in excess of 5°C. This study investigated the early winter period—a time when summer potential evapotranspiration >250 mm has diminished to 8.0°C, comparable to summertime UHI conditions. Through analysis of the Oke (1998) weather factor ΦW, it was determined thermally induced nighttime cool drainage winds could account for inflating the UHI magnitude in winter.

Anthropogenic heat island at Barrow, Alaska, during winter: 2001–2005

The village of Barrow (71°N latitude) is the largest native community in the Arctic, with a population of approximately 4500 people. Situated on the coast of the Arctic Ocean in northernmost Alaska, the area is entirely underlain by permafrost. Although most supplies must be imported, Barrow relies on local natural gas fields to meet all energy requirements for building heat and electrical power generation. This energy eventually dissipates into the atmosphere, and can be detected as a pronounced urban heat island (UHI) in winter. Since 2001, a 150 km2 area in and around Barrow has been monitored using ∼70 data loggers recording air temperature at hourly intervals. The mean daily temperature of the urban and rural areas is calculated using a representative sample of core sites, and the UHI magnitude (MUHI) is calculated as the difference in the group averages. The MUHI is most pronounced in winter months (December–March), with temperatures in the urban area averaging 2°C warmer than in the surrounding tundra and occasionally exceeding 6°C. The MUHI is maximized under cold and calm conditions, and decreases with wind speed and warmer temperatures. It is strongly and directly correlated to natural gas utilization on a monthly basis. Integrated over the home heating season, there is an 8% reduction in freezing degree days in the village. It is unlikely that anthropogenic heat contributes to the forward shift in the snow meltout date that has been observed near Barrow over the past 60 years.

Temporal dynamics of the urban heat island of Singapore

The temporal variability of the canopy-level urban heat island (UHI) of Singapore is examined for different temporal scales on the basis of observations during a 1-year period. Temperature data obtained from different urban areas (commercial, Central Business District (CBD), high-rise and low-rise housing) are compared with ‘rural’ reference data and analysed with respect to meteorological variables and differences in land use. The results indicate that the peak UHI magnitude occurs 3–4 h (>6 h) after sunset in the commercial area, (at other urban sites). Higher UHI intensities generally occur during the southwest monsoon period of May–August, with a maximum of ∼7 °C observed in the commercial area under ideal meteorological conditions. Variations in seasonal precipitation explain some of the differences in urban–rural cooling. No clear relationship between urban geometry and UHI intensity can be seen, and intra-urban variations of temperature are also shown to be influenced by other site factors, e.g. the extent of green space and anthropogenic heat. Lastly, results from the present study are compared with UHI data from other tropical and mid-latitude cities. Copyright © 2006 Royal Meteorological Society.

Assessment with satellite data of the urban heat island effects in Asian mega cities

This study focuses on using remote sensing for comparative assessment of surface urban heat island (UHI) in 18 mega cities in both temperate and tropical climate regions. Least-clouded day- and night-scenes of TERRA/MODIS acquired between 2001 and 2003 were selected to generate land-surface temperature (LST) maps. Spatial patterns of UHIs for each city were examined over its diurnal cycle and seasonal variations. A Gaussian approximation was applied in order to quantify spatial extents and magnitude of individual UHIs for inter-city comparison. To reveal relationship of UHIs with surface properties, UHI patterns were analyzed in association with urban vegetation covers and surface energy fluxes derived from high-resolution Landsat ETM+ data. This study provides a generalized picture on the UHI phenomena in the Asian region and the findings can be used to guide further study integrating satellite high-resolution thermal data with land-surface modeling and meso-scale climatic modeling in order to understand impacts of urbanization on local climate in Asia.

Urban-rural temperature differences in coastal cities: influence of rural sites

This paper considers problems in calculating the heat island magnitude of coastal cities. We examined the influence on heat island magnitude (1) when a rural observatory located in an inland area is compared with an urban observatory and (2) when an observatory in an atypical countryside setting is chosen as the rural site. The results showed that the urban–rural temperature difference was bigger in winter than in summer when the rural observatory was located in a relatively inland area in comparison with the corresponding urban observatory. This tendency was more marked at night than in the daytime. When an observatory in an atypical rural setting was used, the urban–rural temperature difference was greater from 11:00 p.m. to midnight in summer. Therefore, only observatories located in typical rural areas and located roughly the same distance from the sea as the corresponding urban observatories should be selected for investigation of urban heat island magnitude. Copyright © 2005 Royal Meteorological Society

The urban heat island in winter at Barrow, Alaska

AbstractThe village of Barrow, Alaska, is the northernmost settlement in the USA and the largest native community in the Arctic. The population has grown from about 300 residents in 1900 to more than 4600 in 2000. In recent decades, a general increase of mean annual and mean winter air temperature has been recorded near the centre of the village, and a concurrent trend of progressively earlier snowmelt in the village has been documented. Satellite observations and data from a nearby climate observatory indicate a corresponding but much weaker snowmelt trend in the surrounding regions of relatively undisturbed tundra. Because the region is underlain by ice‐rich permafrost, there is concern that early snowmelt will increase the thickness of the thawed layer in summer and threaten the structural stability of roads, buildings, and pipelines. Here, we demonstrate the existence of a strong urban heat island (UHI) during winter. Data loggers (54) were installed in the ∼150 km2 study area to monitor hourly air and soil temperature, and daily spatial averages were calculated using the six or seven warmest and coldest sites. During winter (December 2001–March 2002), the urban area averaged 2.2 °C warmer than the hinterland. The strength of the UHI increased as the wind velocity decreased, reaching an average value of 3.2 °C under calm (<2 m s−1) conditions and maximum single‐day magnitude of 6 °C. UHI magnitude generally increased with decreasing air temperature in winter, reflecting the input of anthropogenic heat to maintain interior building temperatures. On a daily basis, the UHI reached its peak intensity in the late evening and early morning. There was a strong positive relation between monthly UHI magnitude and natural gas production/use. Integrated over the period September–May, there was a 9% reduction in accumulated freezing degree days in the urban area. The evidence suggests that urbanization has contributed to early snowmelt in the village. Copyright © 2003 Royal Meteorological Society

A remote sensing study of the urban heat island of Houston, Texas

Radiative surface temperature maps of Houston, Texas were derived from satellite sensor data acquired at approximately 0400 LST on 27 separate occasions over a two-year period. Urban-rural temperature differences were determined for 21 of these cases by modelling the urban heat island as a twodimensional Gaussian surface superimposed on a planar rural background. The purpose of this study was to characterise the complete urban heat island in magnitude and spatial extent without the use of in situ measurements and to determine whether a correlation exists between heat island magnitude and rural temperature. The urban heat island magnitude was found to be inversely correlated with rural temperature, while the spatial extent was found to be independent of both heat island magnitude and rural temperature.

DYNAMICS AND CONTROLS OF THE NEAR-SURFACE HEAT ISLAND OF VANCOUVER, BRITISH COLUMBIA

Temporal aspects of the urban heat island (UHI) of Vancouver, British Columbia, are demonstrated using differences of screen-level air temperature observed at an urban (downtown) and rural (farmland) site for three years. On an annual basis, the UHI is at its maximum near the middle of the night and its minimum is in mid-afternoon. Growth of the nocturnal UHI is driven by rural cooling rates in the early evening, which are much greater than the almost constant rates in the city. Growth starts earlier in winter. The largest UHI occurs in the fall, and the smallest in the spring. In daytime there is often a “cool island,” especially in summer. There is an approximately inverse square root control of the UHI by wind speed and the effect of cloud type and amount follows the Bolz relation. Combining the two gives a “weather factor” that is linearly related to maximum UHI magnitude. Seasonal variation of the UHI is shown to be inversely related to the thermal admittance of the rural site, which itself is controlled largely by soil moisture status. This is done by calculating a “potential” UHI that is free of weather effects; a value that approximately conforms to that predicted by the SHIM numerical model. Surface wetting caused by recent rain, fog, or melting snow also is found to reduce UHI magnitude. While not quantified, marine advective effects appear to modify the UHI, especially the summer daytime cool island. [Key words: urban heat island (UHI), cooling rates, thermal admittance, Vancouver.]

Associations between varying magnitudes of the urban heat island and the synoptic climatology in Melbourne, Australia

This paper examines the characteristics of the urban heat island (UHI) in a large Australian city (Melbourne) using local area weather data and the US National Centers for Environmental Prediction (NCEP) reanalyses data of mean sea level pressure (MSLP). Conventional methods to determine the UHI from climatological data often involve comparing minimum temperature data between urban and rural environments. The findings presented in this paper show that comparing simultaneous measurements of temperature at one urban and three nearby airport sites at 0600 (Australian eastern standard time (EST)) provided a better estimate of the UHI magnitude. Analyses of these data between 1973–1991 were grouped according to the daily UHI magnitude. For each UHI group of the daily data, mean anomalous synoptic conditions from the 19-year mean monthly MSLP were examined for the influence of the different MSLP conditions on varying UHI magnitudes. These synoptic conditions included the entire range of weather conditions over the study period. Over the 19-year period, daily analyses of the regional climatological 0600 EST temperature data revealed a UHI between −3.16° and 6.0°C. The reanalyses of the NCEP MSLP data, in association with the local area climatological data, suggest that statistically significant anomalous anticyclonic conditions were associated with the warmest 17% and coolest 1% of UHI events. The position of the centre of the anticyclone was critical to UHI genesis and development. Statistically significant mean low pressure anomalies were associated with UHI values between 0° and 1°C. These occurred on 40% of the days between 1973–1991. Melbourne's urban area, independent of the topography, was found to inhibit early morning advection events of warm continent air and result in an urban cool island (UCI). Copyright © 2000 Royal Meteorological Society

A Dimensional Analysis of Urban Heat Island Intensity.

A dimensional analysis is made to relate the magnitude of urban heat island to synoptic conditions andphysical parameters of a city. The proposed relationship is justifiable in view of numerical results and observational data. It shows that the daytime heat island problem could be alleviated by planting more treesand water-fronts, while the nocturnal heat island could be lessened by choosing proper materials for roadsand buildings. Although the validity of this proposed relation should be further examined, it is hoped that therefinement of such a “universal” relation can provide a general guideline to urban designers.

Temperature trends through urbanization in Metropolitan Washington, D.C., 1945?1979

Annual and seasonal changes of the urban heat island magnitude in Washington, D.C. and a close-in suburb were analyzed for the period of 1945 through 1979. Monthly and annual mean temperature data, corrected for elevation, from three stations (National Airport, D.C.—downtown, Silver Spring, MD—suburban, and Beltsville, MD—rural) were evaluated by testing the statistical significance of temperature differences between the different data sets.

Influence of Meteorological Conditions on Urban/Rural Temperature and Humidity Differences for a Small City

Southeastern Geographer Vol. 27, No. 2, November 1987, pp. 90-100 INFLUENCE OF METEOROLOGICAL CONDITIONS ON URBAN/RURAL TEMPERATURE AND HUMIDITY DIFFERENCES FOR A SMALL CITY* DavidJ. Travis, Vernon Meentemeyer and Philip W. Suckling INTRODUCTION. Urban environments have a considerable impact upon meteorological conditions such as temperature and humidity. (1) The concept of the "urban heat island", whereby cities are often warmer than their rural surroundings, is probably the most documented aspect of urban climatology. Even small cities can develop significant heat islands . (2) Warmer urban conditions are best developed under calm clear nocturnal conditions indicating that meteorological controls such as windspeed and cloud cover have a profound effect upon heat island development for a particular city. (3) Urban/rural humidity differences are not as clearly distinguished. (4) It is the purpose of this study to examine urban/rural temperature and humidity differences and the relationship between the day-to-day changes in the state of the atmosphere and the maximum intensity of the urban heat island produced by a small city. A simple model of urban heat island magnitude versus regional meteorological conditions will be presented. METHODOLOGY. This study was conducted during the autumn of 1986 for the urban environment of Athens, Georgia (34°N; 83°W). It has been shown in previous research that urban heat islands are especially welldeveloped in summer and autumn for temperate latitude cities. (5) Athens is a small city with a population of approximately 50,000 within the city limits and a metropolitan population of approximately 100,000. To monitor urban/rural meteorological differences, an "urban" site was selected near the city center close to the area of warmest temperatures detected in a previous temperature transect study. (6) A "rural" site was chosen in an area of small fields and pine forest (typical of the region) located 6 km north of the city center beyond the urban boundary. The * The technical assistance of Doug Oetter is gratefully acknowledged. Mr. Travis is a geography undergraduate student, Dr. Meentemeyer is Professor of Geography and Dr. Suckling is Associate Professor of Geography at the University of Georgia in Athens, GA 30602. Vol. XXVII, No. 2 91 use of single urban and rural sites is a potential limitation to the representativeness of the data obtained. The study was conducted during the autumn of 1986 from 1 October through 10 November. It was the purpose of this study to detect well-established urban/ rural temperature and humidity differences and examine their relationship to regional meteorological conditions. Previous studies have shown that the urban heat island primarily develops due to a lack of urban cooling around and shortly after sunset, i.e., a lesser urban cooling rate. (7) Thus, the maximum heat island magnitude is established within a few hours of sunset. Based on these facts, data were collected for the present study beginning 90 minutes after official sunset. The rural site was monitored first, then the urban site, followed by a return to the rural site. All measurements were completed within two hours of sunset. The two rural measurements were averaged to yield the final rural data in order to compensate for temporal change. The two rural temperature measurements consistently differed by less than 1.50C indicating that cooling rates, typically rapid around sunset, had moderated considerably by the measurement times for this study. Wet and dry bulb temperatures were monitored at both sites using a Cole-Parmer type K thermocouple probe with wet and dry bulb sensors. A standard sling Psychrometer was used to confirm the response of the thermocouple probe. Due to instrument failure, temperature and humidity data for November 9 were missed while humidity data for October 16 were lost. The number of available observations of urban/rural temperature conditions was therefore 40, while humidity observations were available for 39 days. To represent the general regional meteorological conditions, hourly values of temperature (T), relative humidity (RH), vapor pressure (e), cloud cover amount (cc), and windspeed (u) were obtained from the National Weather Service (NWS) station located at Athens airport (approximately 6 km east of the city center) for appropriate times corresponding to the urban/rural field measurements. The NWS site, located on the suburban fringe...

Nocturnal observations of incoming longwave radiation and the urban heat island for a small prairie city

Observations of incoming Longwave radiation (L↓) and air temperature were made using automobile transects across the small city of Brandon, Canada. Data were obtained during nighttime for 13 spring and summer days in 1979 under a variety of sky cover conditions. A strong relationship between urban-rural differences inL↓ and the urban heat island magnitude was found. Values ofL↓ were consistently larger for the urban situation with increases over the rural case ranging from 2.0 to 20.1% with an average of 10.7%. These increases are comparable to those found in past studies for much larger cities.