Urban Surface Temperature Research Articles

Urban surface heat fluxes infrared remote sensing inversion and their relationship with land use types

Using ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) infrared remote sensing data we inversed the parameters of urban surface heat fluxes applying the PCACA model and theoretical position algorithm, and then we analyzed the influence of different land use types on the surface heat fluxes and energy balance. In this study, Kumagaya, a city in Saitama Prefecture, Japan, was selected as the experimental area. The result shows that the PCACA model is feasible for the surface heat fluxes estimation in urban areas because this model requires less parameters in the procedure of heat fluxes estimation in urban areas with complicated surface structure and can decrease the uncertainty. And we found that different land-use types have indicated the height heterogeneity on the surface heat fluxes significantly. The magnitudes of Bowen ratio in descending order are industrial, residential, transportation, institutional, dry farmland, green space, and water body. Under the same meteorological condition, there are distinct characteristics and regional differences in Bowen ratios among different surface covers, indicating higher sensible heat flux and lower latent heat flux in the urban construction land, while lower sensible heat flux and higher latent heat flux in the vegetation-covered area, the outskirt of the urban area. The increase of urban impervious surface area caused by the urban sprawl can enlarge the sensible heat flux and the Bowen ratio, so that it causes the increasing of urban surface temperature and air temperature, which is the mechanism of the so-called heat island effect.

Interpolating diurnal surface temperatures of an urban facet using sporadic thermal observations

The interpolation of urban surface temperatures (USTs) is crucial to the utilization of temporally sporadic observations from satellites and to understanding urban climate. This study directly connects diurnal USTs with thermal inertia and presents a physically based approach to interpolate the diurnal USTs of an urban facet with sporadic thermal observations. Analytical and numerical methods are combined to solve the heat conduction equation constrained by a multi-force boundary condition. The diurnal flat surface temperatures and the diurnal air temperatures are parameterized to denote the environmental forcing. The results indicate that both the diurnal flat surface temperatures and the diurnal air temperatures are good options, but the former are better than the latter at representing environmental forcing in urban canyons. Data from both the real building and the scale model are utilized in validations, and results show that the interpolated root mean square errors of the UST are within 2 K. The inter-comparison between methods also suggests the presented model is efficient for predicting USTs with discontinuous thermal observations.

Developing an Index to Measure Urban Heat Island Effect Using Satellite Land Skin Temperature and Land Cover Observations

Abstract A new index of calculating the intensity of urban heat island effects (UHI) for a city using satellite skin temperature and land cover observations is recommended. UHI, the temperature difference between urban and rural regions, is traditionally identified from the 2-m surface air temperatures (i.e., the screen-level temperature T2m) measured at a pair of weather stations sited in urban and rural locations. However, such screen-level UHI is affected by the location, distance, and geographic conditions of the pair of weather stations. For example, choosing a different pair of rural and city sites leads to a different UHI intensity for the same city, due to the high heterogeneity of the urban surface temperature. To avoid such uncertainty, satellite-observed surface skin temperature measurements (i.e., skin level temperature Tskin) is recommended to record UHI, known as skin-level UHI or UHIskin. This new index has advantages of high spatial resolution and aerial coverage to better record UHI intensity than T2m. An assessment of skin-level UHI from 10 yr of the National Aeronautics and Space Administration (NASA)’s Moderate Resolution Imaging Spectroradiometer (MODIS) observations reveals that skin-level UHI has a strong UHI signal during the day and at night. In addition, there are significant diurnal and seasonal variations in skin-level UHI. Furthermore, the skin-level UHI is stronger during the day and summer (July) than during nighttime and winter. This new index is important for more uniformly assessing UHIs over cities around the globe. Nevertheless, whether the seasonality and diurnal variations revealed in this work using skin-level UHI index are valid over desert cities, such as Phoenix, Arizona, need to be examined.

Assessment of thermal anisotropy on remote estimation of urban thermal inertia

Thermal inertia over vast earth surfaces is a crucial parameter in many related disciplines. However, remote estimates of urban thermal inertia show anisotropy effects due to thermal anisotropy. This study investigates the impacts of thermal anisotropy on the estimation of urban thermal inertia. We present the concepts of DTI (directional thermal inertia) and DATI (directional apparent thermal inertia) to describe this anisotropic effect. A combined approach to estimating thermal inertia named NLS (nonlinear least square) is proposed as a compromise solution using temporal temperature measurements. Intercomparisons between methods are indirectly conducted by predicting surface temperatures, and the results indicate the NLS has higher accuracy of 1 to 2K. The DTI estimation over an urban scale model, together with flat concrete and grass surfaces, reveals that the DTI intensity is significant when DRTs (directional radiometric temperatures) are used as inputs. Over the scale model, the DTI and DATI values range from 0.028 to 0.038K−1 and from 1530 to 2970W∙s1/2∙m−2∙K−1 if the zenith and azimuth are between −60° and +60° and between 0° and +360°, respectively. Further discussions demonstrate that DRT intensity has an approximate linear relationship with DTI intensity and that it thus could be used as a predictor of DTI intensity. We finally propose that using complete urban surface temperatures instead of the DRT would be better to estimate urban thermal inertia from the perspective of surface energy balance.

Urban Heat Island Effect Analysis around Hangzhou Bay between 2005 and 2009 Using Remotely Sensed Data

By taking advantage of temporal and spatial remote sensing, the present paper was to map, identify and characterize urban heat island in rapid urbanization area of east China. For research areas including six metropolitan cities around Hangzhou bay in east China, urban heat island measurements were monitored from surface temperature maps at 1km resolution derived from MOD11A2 both day and night acquired in the year of 2005 and 2009. LST normalization with NDSTI was applied in order to quantify UHI spatial changes at four seasons. The result showed that urban heat island phenomenon expanded contiguously in the study area. Day change of UHI seems to be more chaos than night change due to day UHI influenced by both solar and human being activities. There was some kind of urban cool island phenomenon in winter when urban surface temperatures were to be -1 – 0°C lower than the ambient LST. Except for winter, other seasons' UHI during daytime changed from 0.5°C to 2.5 °C and nighttime strongly changed from 0.5°C to 5 °C in 2009. During the night, six cites' UHI roughly coincides and UHI in winter was the smallest and in autumn was the biggest one. The study provided causation and environmental awareness of urbanization to urban planners in future urban development.

Urban surface temperature and microclimate measurements in Thessaloniki

The urbanization and the deficiencies in proper development control have as consequence the environment's degradation in urban centres and the change of microclimatic conditions. So, the urban microclimate of densely built areas is characterized by higher temperatures than the temperature of the suburbs and surrounding areas. Heating of the atmosphere and surfaces in urban areas compared to their surroundings is the phenomenon which is called urban heat island (UHI). The effect of building's volume is considered as one of the main reasons for the urban heat island effect. Buildings, roads and paved surfaces, store the heat during the day and then release it slowly during the evening keeping the air temperature of the city hotter than surrounding areas. In other words, urban heat island cause thermal discomfort and it is responsible for the increase of energy demand in the buildings. This paper presents a study that aims at investigating the influence of urban morphology in microclimatic conditions. The investigation is carried out in Thessaloniki, Greece. The purpose of the research project is to measure how the temperature of building's surfaces vary and interact during the day and according to the microclimatic parameters. There is a daily measurement of the examinated factors. Street orientation and configuration of the building blocks (height of buildings, width of road) are also important factors for the analysis of the measurements.

Exploring indicators for quantifying surface urban heat islands of European cities with MODIS land surface temperatures

The term urban heat island describes the phenomenon of altered temperatures in urban areas compared to their rural hinterlands. A surface urban heat island encompasses the patterns of land surface temperatures in urban areas. The classical indicator to describe a surface urban heat island is the difference between urban and rural surface temperatures. However, several other indicators for this purpose have been suggested in the literature. In this study, we compared the eleven different indicators for quantifying surface urban heat islands that were most frequently used in recent publications on remote sensing-based urban heat island assessments. The dataset used here consists of 263 European cities with monthly mean temperatures from MODIS data products for July 2002, January 2003 and July 2003. We found that (i) the indicators individually reveal diurnal and seasonal patterns but show rather low correlations over time, and (ii) for single points in time, the different indicators show only weak correlations, although they are supposed to quantify the same phenomenon. Differentiating cities according to thermal climate zones increased the relationships between the indicators. Thus, we can identify temporal aspects and indicator selection as important factors determining the estimation of urban heat islands. We conclude that research should take into account the differences and instabilities of the indicators chosen for quantifying surface urban heat islands and should use several indicators in parallel for describing the surface urban heat island of a city.

Identification and analysis of urban surface temperature patterns in Greater Athens, Greece, using MODIS imagery

Thermal infrared images are being acquired by satellites for more than two decades enabling studies of the human-induced Urban Heat Island (UHI) phenomenon. As a result, the requirement of the scientific community for fast and efficient methods for extracting and analyzing the thermal patterns from a vast volume of acquired data has emerged. The present paper proposes an innovative object-based image analysis procedure to extract thermal patterns for the quantitative analysis of satellite-derived Land Surface Temperature (LST) maps. The spatial and thermal attributes associated with these objects are then calculated and used for the analyses of the intensity, the position and the spatial extent of UHIs. A case study was conducted in the Greater Athens Area, Greece. More than 3000 LST images of the area acquired by MODIS sensor over a decade were analyzed. Three daytime hot-spots were identified and studied (Megara, Elefsina-Aspropyrgos and Mesogeia). They were all found to exhibit similar behavior, gradually increasing their maximum temperature during the summer season and reaching their maxima in mid-July. The hot-spots' thermal intensities compared to a suburban area were of 9–10 °C and were found to be highly correlated to their areal extent. During the night-time, Athens center developed a typical UHI spatially coinciding with the dense urban fabric. The nighttime maximum LST peaked (on average) at the end of July, two weeks later than the daytime surface patterns. The mean spatial extent of UHI in Athens was 55.2 km 2, whilst its mean intensity was 5.6 °C. The proposed automatic extraction process can be customized for other cities and potentially used for comparison of LST patterns and UHI behavior between different cities.

The Performance of Low-Heat Accumulation Asphalt Mixture and the Evaluation Model of its Thermal Effect on Cities

A new type of low-heat accumulation asphalt concrete material has been made to reduce urban surface temperature and to ease the urban heat island effect. The test has investigated the temperature reduction performance and pavement performance, established a non-gray model of the atmospheric temperature field, and evaluated its effect on the urban thermal environment. The results show that compare specimens mixed with infrared powder with normal ones, the higher the infrared powder content, the lower the surface temperature, but the cooling rate decreases; the properties of high-temperature stability, low-temperature stability and water stability are improved; under the same temperature and humidity conditions, the surface layer temperature of the former pavement is lower generally; under the same radiation conditions, the surface equilibrium temperature of the former ones is 8.12K lower, which can reduce the near-earth atmospheric temperature and ease the urban heat island effect.

Impact of non-uniform urban surface temperature on pollution dispersion in urban areas

Airflow pattern through street canyons has been widely studied to understand the nature of pollution dispersion in order to develop guidelines for urban planners. One of the major contributing parameters in pollution dispersion is thermal-induced flow caused by surface and air temperature difference. However, most of the previous studies assumed isothermal condition for street canyons. Those addressed the thermal-induced flow, have assumed a uniform wall surface temperature distribution. The external building wall surface temperature distribution is not uniform, and is influenced by many factors including the wall surface characteristics, and shading. The non-uniform temperature distribution significantly impacts on 3-dimensional airflow within street canyons. Moreover, effect of intersection is barely considered in the literature where L/H<3 (L and H are respectively length and height of street canyon). This Paper reports the development of a 3-dimensional model to study the effect of non-uniform wall surface temperature distribution on the pollution dispersion and flow pattern within the short street canyons (L/H<3). For this purpose, a computational fluid dynamics (CFD) model is developed to investigate these effects on pollution dispersion in various prevailing wind velocities and directions. Moreover, active and passive techniques to reduce the level of concentration are examined. The study clearly shows that thermal-induced flow dominates during fair-weather condition.

Monitoring of urban heat island effect in Beijing combining ASTER and TM data

This paper focuses on the monitoring of the urban heat island (UHI) effect with temporal and spatial variation, combining Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Thematic Mapper (TM) data. Our study area is located in the central urban area of Beijing, which mainly refers to the areas within the fifth ring road. For detecting UHI changes over the years 2002–2006, three ASTER images in the summers of 2003, 2004 and 2006 and two TM datasets in the summers of 2002 and 2005 were collected. For monitoring UHI changes with the seasons, three ASTER images and one TM image in 2004 in winter, spring, summer and autumn, respectively, were employed. To calculate the urban heat island intensity, the land surface temperatures were retrieved iteratively for ASTER data and using a generalized single-channel method for the TM image. Four separated regions located in four directions outside the fifth ring road were selected as representing rural comparative regions. Their averaged land surface temperature was regarded as the rural comparative temperature. The UHI intensity was computed by the difference between the pixel urban land surface temperature in the urban area and the comparative temperature in the rural area. Detection of the UHI effect over 2002 to 2006 indicated that most of the areas with high UHI effect were the industrial land use regions and the areas having a high density of buildings, roads, transportations and residents; and the areas without UHI effect were located around the regions with large areas of grassland, trees and water bodies. Our results also showed that the UHI effect was not proportional to urbanization over time. Statistical UHI data during 20 July to 20 September in 2003–2008 also support this point. The monitoring of the UHI effect over seasons (winter, spring, summer and autumn) showed that the urban area of Beijing city had a high UHI effect except in winter, when the urban area of Beijing was in an urban heat sink; the UHI effect increased in spring, summer and autumn.

Health Impact of Heat Waves in Urban Heat Islands: How to Estimate the Exposure of the Population?

PP-30-084 Background/Aims: Heat waves are particularly deadly in large cities where the distribution of surface heat fluxes is altered compared with natural areas. This could be reinforced by climate change. The objectives were to analyze the urban surface temperatures, and to build a new risk indicator of exposure according to the residence location. Methods: The study is based on 61 thermal images at 1-km resolution, sensed by the NOAA-AVRR satellites during the 1–13 August 2003 heat wave, and a case-control study concerning 482 persons aged 65 or more, living in the Paris region (France) at that time. For each person, minimal, maximal, and mean temperature indices were built for different periods, and integrated into a conditional logistic regression model to test their use as exposure indicator and their effect on mortality. The model was adjusted on other risk factors such as age, sex, socioeconomic conditions, autonomy, behavior of heat adaptation, health problems, housing, and geographical district. Results: The observed surface temperature amplitude ranged from 12.18°C to 45.41°C, with a median at 21.4°C at night and 34.2°C during day. The differences of surface temperatures between cases and controls ranged from −6.1°C to 8.4°C. The results of the analysis are statistically significant for minimal temperatures computed from 1st to 13th August, and for minimal temperature averaged on the period going from the day of the death to the sixth preceding day (OR of 2.57 and 2.22, respectively). Conclusion: The results confirm the significant health effect of night-time high temperature, and point out the location and time of heat islands. Such data could be used for long-term prevention, by targeting the districts where intervention is a priority. Studying the links between night temperatures and urban characteristics should help public health authorities and planning agencies to determine the better actions for reducing heat islands.

A Spatially-Analytical Scheme for Surface Temperatures and Conductive Heat Fluxes in Urban Canopy Models

In the urban environment, surface temperatures and conductive heat fluxes through solid media (roofs, walls, roads and vegetated surfaces) are of paramount importance for the comfort of residents (indoors) and for microclimatic conditions (outdoors). Fully discrete numerical methods are currently used to model heat transfer in these solid media in parametrisations of built surfaces commonly used in weather prediction models. These discrete methods usually use finite difference schemes in both space and time. We propose a spatially-analytical scheme where the temperature field and conductive heat fluxes are solved analytically in space. Spurious numerical oscillations due to temperature discontinuities at the sublayer interfaces can be avoided since the method does not involve spatial discretisation. The proposed method is compared to the fully discrete method for a test case of one-dimensional heat conduction with sinusoidal forcing. Subsequently, the analytical scheme is incorporated into the offline version of the current urban canopy model (UCM) used in the Weather Research and Forecasting model and the new UCM is validated against field measurements using a wireless sensor network and other supporting measurements over a suburban area under real-world conditions. Results of the comparison clearly show the advantage of the proposed scheme over the fully discrete model, particularly for more complicated cases.

URBAN HEAT ISLAND UNDER IMPACT OF URBANIZATION IN HOCHIMINH CITY FROM REMOTE SENSING DATA

This paper presents the formation of urban heat island under the impact of urbanization in Hochiminh City in 1989-2006. Urbanization with increasing impervious surfaces impacted the common temperature background over the city by the warm rising trend. The results of applying remote sensing method extracting urban surface temperature defined the magnitude and space extension of “Surface urban heat island”, where the differences of surface temperature between urban and rural areas on 2006 image were about 11oC – 12oC. The magnitude of surface urban heat island increased in 6 to 26 times, particularly the biggest heat island was concentrated in the inner city with the area about 29.000ha. Urban heat island greatly influences the environment and the human health. Therefore, it is necessary to act on reducing the temperature of heat island in order to make our city more friendly to environment, to ensure human health, to decrease the energy demand and waste of water by sustainable development goal.

Investigating spatial non-stationary and scale-dependent relationships between urban surface temperature and environmental factors using geographically weighted regression

Despite growing concerns for the variation of urban thermal environments and driving factors, relatively little attention has been paid to issues of spatial non-stationarity and scale-dependence, which are intrinsic properties of the urban ecosystem. In this paper, using Shenzhen City in China as a case study, a geographically weighted regression (GWR) model is used to explore the scale-dependent and spatial non-stationary relationships between urban land surface temperature ( LST) and environmental determinants. These determinants include the distance between city and highway, patch richness density of forestland, wetland, built-up land and unused land and topographic factors such as elevation and slope aspect. For reference, the ordinary least squares (OLS) model, a global regression technique, was also employed, using the same response variable and explanatory variables as in the GWR model. The results indicate that the GWR model not only provides a better fit than the traditional OLS model, but also provides local detailed information about the spatial variation of LST, which is affected by geographical and ecological factors. With the GWR model, the strength of the regression relationships increased significantly, with a mean of 59% of the changes in the LST values explained by the predictors, compared with only 43% using the OLS model. By computing a stationarity index, one finds that different predictors have different variational trends which tend towards the stationary state with the coarsening of the spatial scale. This implies that underlying natural processes affecting the land surface temperature and its spatial pattern may operate at different spatial scales. In conclusion, the GWR model is an alternative approach to addressing spatial non-stationary and scale-dependent problems in geography and ecology.

Experimental study of practical applications of a passive evaporative cooling wall with high water soaking-up ability

Aimed at controlling the increase in urban surface temperature and creating comfortable urban environments in summer, the authors have developed a passive evaporative cooling wall (PECW) constructed of porous ceramics. These ceramics enable their vertical surfaces to be wet up to a level higher than 100 cm when their lower end is placed in water. Our previous study has demonstrated the cooling performance and applicability of a prototype PECW constructed of pipe-shaped ceramics (ceramic pipes). The present paper presents a PECW unit system which can be easily installed for practical applications. Experiments were conducted using experimental PECW units. Experimental results show that the ceramic pipe developed in this study possessed a higher water-holding and soaking-up ability than the previous one. Wet surfaces of the new ceramic pipe reached a height of over 130 cm at an outdoor location exposed to solar radiation on sunny summer days. Furthermore, the air passing through the PECW unit was cooled, and its temperature can be reduced by around 2 °C during summer daytime. These results indicate that the proposed PECW can be broadly applied to various urban locations.

Modeling the Thermal Effects of Artificial Turf on the Urban Environment

Abstract The effects of artificial turf (AT) on the urban canopy layer energy balance, air and surface temperatures, and building cooling loads are compared to those of other common ground surface materials (asphalt, concrete, and grass) through heat transfer modeling of radiation, convection, and conduction. The authors apply the Temperatures of Urban Facets in 3D (TUF3D) model—modified to account for latent heat fluxes—to a clear summer day at a latitude of 33° over a typical coastal suburban area in Southern California. The low albedo of artificial turf relative to the other materials under investigation results in a reduction in shortwave radiation incident on nearby building walls and an approximately equal increase in longwave radiation. Consequently, building walls remain at a relatively cool temperature that is similar to those that are adjacent to irrigated grass surfaces. Using a simple offline convection model, replacing grass ground cover with artificial turf was found to add 2.3 kW h m−2 day−1 of heat to the atmosphere, which could result in urban air temperature increases of up to 4°C. Local effects of AT on building design cooling loads were estimated. The increased canopy air temperatures with AT increase heat conduction through the building envelope and ventilation in comparison with a building near irrigated grass. However, in this temperate climate these loads are small relative to the reduction in radiative cooling load through windows. Consequently, overall building design cooling loads near AT decrease by 15%–20%. In addition, the irrigation water conservation with AT causes an embodied energy savings of 10 W h m−2 day−1. Locally, this study points to a win–win situation for AT use for urban landscaping as it results in water and energy conservation.

IMPACT OF URBAN EXPANSION ON SURFACE TEMPERATURE IN BAGHDAD, IRAQ USING REMOTE SENSING AND GIS TECHNIQUES

Baghdad city has experienced a rapid urban expansion over the last decades due to accelerated economic growth. This paper reports an investigation into the application of the integration of remote sensing and geographic information systems (GIS) for detecting urban built up growth for the period 1961-2002, and evaluate its impact on surface temperature in Baghdad city. The purpose of this study is to analysis and verifies the spatial distribution property of the surface temperature with urban spatial information, related with land cover / land use and NDVI using remotely sensed data and GIS. Surface temperature, land cover pattern and NDVI were extracted from Landsat7 ETM + data. Then surface temperatures, was linked to land use data of Baghdad region for further investigations of the relationship between temperature behavior and urban structures. The Normalized Difference Vegetation Index (NDVI) was used to examine the relation between thermal behavior and vegetation cover amount. The results showed that the negative average correlation more than 85 % was identified by the results from the correlation and regression analysis of the extracted surface temperature from Landsat data image with NDVI. Also this research verified the distribution of urban surface temperature was very different depends on various land cover type of surrounding areas. Water and forest cover types show low day temperature differences compared to residential, commercial cover types. The integration of remote sensing and GIS was found to be effective in monitoring and analyzing urban growth patterns and in evaluating urbanization impact on surface temperature.

Study of the Impact of Urban Development on Surface Temperature Using Remote Sensing in Ho Chi Minh City, Southern Vietnam

AbstractRapid urbanisation and industrialisation have resulted in sharp land cover changes. Urban change not only impacts on land cover but also on urban climate. Land surface and atmospheric modifications due to urbanisation generally lead to a modified thermal climate that is warmer than the surrounding, non‐urbanised areas. In this research remote sensing technology was used to evaluate urban growth patterns and its thermal characteristics through mapping impervious surfaces and evaluating thermal infrared images. The case study was carried out in the northern part of Ho Chi Minh City, which has experienced accelerated urban development since the late 1980s. Landsat and Aster images were used to calculate variations in urban impervious surfaces from 1989 to 2006. Thermal bands were processed to obtain radiant surface temperatures for investigating the urban heat island effect associated with increasing impervious surfaces, both spatially and temporally. Impacts of urban development on surface temperature were shown by investigating the surface urban heat island effect intensity. The results show that the built‐up area in the northern part of Ho Chi Minh City expanded by 6.5 times between 1989 and 2006. Urban development has altered the magnitude and pattern of the surface urban heat island, with the highest land surface temperature cores found in the industrial (greater than 45oC) and urban areas (within 36oC and 40oC). In suburban and rural areas, where agricultural land still remains with full vegetation cover, the land surface temperature is usually lower. Using remote sensing, the impervious surface was extracted with overall accuracy and a Kappa coefficient for all three years greater than 96%, and the retrieved land surface temperatures with variations from in‐situ measurements of less than 2oC. The results presented here indicate that remote sensing can help to spatially monitor urban development and land surface temperature changes over the whole area and over a long period of time.

Urban Surface Temperature Reduction via the Urban Aerosol Direct Effect: A Remote Sensing and WRF Model Sensitivity Study

The aerosol direct effect, namely, scattering and absorption of sunlight in the atmosphere, can lower surface temperature by reducing surface insolation. By combining National Aeronautics and Space Administration (NASA) AERONET (AErosol RObotic NETwork) observations in large cities with Weather Research and Forecasting (WRF) model simulations, we find that the aerosol direct reduction of surface insolation ranges from 40–100Wm−2, depending on aerosol loading and land‐atmosphere conditions. To elucidate the maximum possible effect, values are calculated using a radiative transfer model based on the top quartile of the multiyear instantaneous aerosol data observed by AERONET sites. As a result, surface skin temperature can be reduced by 1°C‐2°C while 2‐m surface air temperature reductions are generally on the order of 0.5°C–1°C.