Spatial Variation Of Surface Temperature Research Articles

Understanding land surface temperature on rift areas to examine the spatial variation of urban heat island: the case of Hawassa, southern Ethiopia

Examining the spatial variation of surface temperature is an important criterion to create livable urban environment. To examine the cause of heat island variation in the study area located within the rift zones, an algorithm that was prepared for Landsat 8 band 10 were used by taking the Normalized Difference Vegetation Index threshold method for the estimation of ground emissivity by integrating with the result obtained from MODIS night time data. The LU/LC (land use land cover) maps of the area were prepared with better accuracy using on screen classification technique. The derived LST showed that the surface temperature of the city ranges from 20.6 to 41.30 °C and the minimum temperature of the area was observed within the lake and the surrounding areas such as wetland. The maximum temperature was registered on the scattered hills and excavation areas and some parts of bare lands including industrial park of the city. The spatial variation of LST (Land Surface Temperature) in the city is the result of three major factors namely: (1) volcanic products of the geological setting, (2) the nature of the rock (high reflectance) and (3) the LU/LC type. Increasing of evergreen tree cover and rehabilitation of existing mining areas are among the recommended strategy to mitigate the UHI (urban heat island) effects in the city. For future studies in areas that are susceptible to natural heat sources, the satellite data should have high spatial resolution and derived from multiple sensors and satellites that can provide better tools to understand the UHI effect considering the geological setting of the area.

Diurnal Variations of the Flux Imbalance Over Homogeneous and Heterogeneous Landscapes

It is well known that the sum of the turbulent sensible and latent heat fluxes as measured by the eddy-covariance method is systematically lower than the available energy (i.e., the net radiation minus the ground heat flux). We examine the separate and joint effects of diurnal and spatial variations of surface temperature on this flux imbalance in a dry convective boundary layer using the Weather Research and Forecasting model. Results show that, over homogeneous surfaces, the flux due to turbulent-organized structures is responsible for the imbalance, whereas over heterogeneous surfaces, the flux due to mesoscale or secondary circulations is the main contributor to the imbalance. Over homogeneous surfaces, the flux imbalance in free convective conditions exhibits a clear diurnal cycle, showing that the flux-imbalance magnitude slowly decreases during the morning period and rapidly increases during the afternoon period. However, in shear convective conditions, the flux-imbalance magnitude is much smaller, but slightly increases with time. The flux imbalance over heterogeneous surfaces exhibits a diurnal cycle under both free and shear convective conditions, which is similar to that over homogeneous surfaces in free convective conditions, and is also consistent with the general trend in the global observations. The rapid increase in the flux-imbalance magnitude during the afternoon period is mainly caused by the afternoon decay of the turbulent kinetic energy (TKE). Interestingly, over heterogeneous surfaces, the flux imbalance is linearly related to the TKE and the difference between the potential temperature and surface temperature, ΔT; the larger the TKE and ΔT values, the smaller the flux-imbalance magnitude.

Prediction model of microclimatic surface conditions on building façades

The microclimatic surface conditions of a building façade are critical for determining the degradation of the façade material. Most models use the ambient temperature and RH to predict mould growth and decay on building materials. On the other hand, Heat, Air and Moisture (HAM) simulation software able to calculate the surface conditions, treats the whole façade uniformly without including architectural characteristics of the façade, such as window sills or overhangs, which can have shadowing effect. A simulation model that takes into consideration both the local microclimate and the spatial architectural characteristics of the façade has been developed to predict the spatial surface temperature and moisture content over a whole façade. The model is validated through measurements for two different building façades – wooden consisting of aspen (Populus tremula) and masonry consisting of red fire clay bricks. The measurements include monitoring of the spatial surface temperatures with an infrared camera, and logging of the surface moisture content of selected points on the façade using wood resistance humidity sensors. The validation shows that the simulation model can predict the microclimatic surface conditions with high accuracy and can sufficiently capture the spatial variations of surface temperature and moisture content over a building façade.

Monitoring surface urban heat island formation in a tropical mountain city using Landsat data (1987–2015)

Since it was first described about two centuries ago and due to its adverse impacts on urban ecological environment and the overall livability of cities, the urban heat island (UHI) phenomenon has been, and still is, an important research topic across various fields of study. However, UHI studies on cities in mountain regions are still lacking. This study aims to contribute to this endeavor by monitoring and examining the formation of surface UHI (SUHI) in a tropical mountain city of Southeast Asia –Baguio City, the summer capital of the Philippines– using Landsat data (1987–2015). Based on mean surface temperature difference between impervious surface (IS) and green space (GS1), SUHI intensity (SUHII) in the study area increased from 2.7°C in 1987 to 3.4°C in 2015. Between an urban zone (>86% impervious) and a rural zone (<10% impervious) along the urban-rural gradient, it increased from 4.0°C in 1987 to 8.2°C in 2015. These results are consistent with the rapid urbanization of the area over the same period, which resulted in a rapid expansion of impervious surfaces and substantial loss of green spaces. Together with landscape composition variables (e.g. fraction of IS), topographic variables (e.g. hillshade) can help explain a significant amount of spatial variations in surface temperature in the area (R2=0.56–0.85) (p<0.001). The relative importance of the ‘fraction of IS’ variable also increased, indicating that its unique explanatory and predictive power concerning the spatial variations of surface temperature increases as the city size becomes bigger and SUHI gets more intense. Overall, these results indicate that the cool temperature of the study area being situated in a mountain region did not hinder the formation of SUHI. Thus, the formation and effects of UHIs, including possible mitigation and adaptation measures, should be considered in landscape planning for the sustainable urban development of the area.

ANALYSIS OF THE INTRA-CITY VARIATION OF URBAN HEAT ISLAND AND ITS RELATION TO LAND SURFACE/COVER PARAMETERS

Abstract. Along with urbanization, sealing of vegetated land and evaporation surfaces by impermeable materials, lead to changes in urban climate. This phenomenon is observed as temperatures several degrees higher in densely urbanized areas compared to the rural land at the urban fringe particularly at nights, so-called Urban Heat Island. Urban Heat Island (UHI) effect is related with urban form, pattern and building materials so far as it is associated with meteorological conditions, air pollution, excess heat from cooling. UHI effect has negative influences on human health, as well as other environmental problems such as higher energy demand, air pollution, and water shortage. Urban Heat Island (UHI) effect has long been studied by observations of air temperature from thermometers. However, with the advent and proliferation of remote sensing technology, synoptic coverage and better representations of spatial variation of surface temperature became possible. This has opened new avenues for the observation capabilities and research of UHIs. In this study, "UHI effect and its relation to factors that cause it" is explored for İzmit city which has been subject to excess urbanization and industrialization during the past decades. Spatial distribution and variation of UHI effect in İzmit is analysed using Landsat 8 and ASTER day &amp;amp; night images of 2015 summer. Surface temperature data derived from thermal bands of the images were analysed for UHI effect. Higher temperatures were classified into 4 grades of UHIs and mapped both for day and night. Inadequate urban form, pattern, density, high buildings and paved surfaces at the expanse of soil ground and vegetation cover are the main factors that cause microclimates giving rise to spatial variations in temperatures across cities. These factors quantified as land surface/cover parameters for the study include vegetation index (NDVI), imperviousness (NDISI), albedo, solar insolation, Sky View Factor (SVF), building envelope, distance to sea, and traffic space density. These parameters that cause variation in intra-city temperatures were evaluated for their relationship with different grades of UHIs. Zonal statistics of UHI classes and variations in average value of parameters were interpreted. The outcomes that highlight local temperature peaks are proposed to the attention of the decision makers for mitigation of Urban Heat Island effect in the city at local and neighbourhood scale.

ASTER‐based study of the night‐time urban heat island effect in Metro Manila

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was used to derive land surface temperatures to quantify the night‐time urban heat island (UHI) effect in Metro Manila. Temperature differences between Metro Manila and its adjacent rural towns were compared to determine heat island intensity and analyse spatial variation of surface temperature. Transects were drawn across from the rural to the urban region to characterize the UHI profile and the Normalized Difference Vegetation Index (NDVI) was used to examine the relationship between amount of vegetation and temperature. The thermal images revealed the highest UHI intensity to be 2.96°C with the presence of a heat island existing in the central part of the city. The transects described the cross‐sectional heat island profile characterized by gradients of ‘cliffs’, ‘plateaus’ and a ‘peak’ occurring in the city centre. The study also showed an inverse relationship between NDVI and temperature, which suggests that increasing the amount of plants in cities can reduce the UHI effect.

Scale Modelling of Nocturnal Cooling in Urban Parks

Scale modelling is used to determine the relative contribution of heat transfer processes to the nocturnal cooling of urban parks and the characteristic temporal and spatial variation of surface temperature. Validation is achieved using a hardware model-to-numerical model-to-field observation chain of comparisons. For the calm case, modelling shows that urban-park differences of sky view factor (ψs) and thermal admittance (μ) are the relevant properties governing the park cool island (PCI) effect. Reduction in sky view factor by buildings and trees decreases the drain of longwave radiation from the surface to the sky. Thus park areas near the perimeter where there may be a line of buildings or trees, or even sites within a park containing tree clumps or individual trees, generally cool less than open areas. The edge effect applies within distances of about 2.2 to 3.5 times the height of the border obstruction, i.e., to have any part of the park cooling at the maximum rate a square park must be at least twice these dimensions in width. Although the central areas of parks larger than this will experience greater cooling they will accumulate a larger volume of cold air that may make it possible for them to initiate a thermal circulation and extend the influence of the park into the surrounding city. Given real world values of ψs and μ it seems likely that radiation and conduction play almost equal roles in nocturnal PCI development. Evaporation is not a significant cooling mechanism in the nocturnal calm case but by day it is probably critical in establishing a PCI by sunset. It is likely that conditions that favour PCI by day (tree shade, soil wetness) retard PCI growth at night. The present work, which only deals with PCI growth, cannot predict which type of park will be coolest at night. Complete specification of nocturnal PCI magnitude requires knowledge of the PCI at sunset, and this depends on daytime energetics.