Estimating spatial and temporal patterns of urban anthropogenic heat fluxes for UK cities: the case of Manchester

A model is proposed for determining the temporal and spatial patterns of anthropogenic heat fluxes in UK urban areas. It considers buildings, traffic, and metabolic heat flux sources and has been evaluated to a good accuracy against alternative data for the Greater Manchester area in the UK. Results are presented at spatial resolution of 200 ×?200 m although the model itself is scalable depending on data availability. In this paper, results are generated using a set of urban morphology units so that detailed and time-consuming accounting of individual building and road emissions is not required. The model estimates a mean heat emission of 6.12 Wm^-2 across Greater Manchester, with values in the region of 10 Wm^-2 for non central urbanized areas and 23 Wm^-2 in city center areas. Despite this difference, the results are not described by a simple distance decay function, as has been reported for other cities, due to the influence of satellite towns and the influence of the road network. Buildings are the dominant emitter, contributing some 60% of total emissions across the city compared to around 32% for road traffic and 8% for metabolic sources.     

Estimation of urban heat island intensity using biases in surface air temperature simulated by a nonhydrostatic regional climate model

This study demonstrates that urban heat island (UHI) intensity can be estimated by comparing observational data and the outputs of a well-developed high-resolution regional climate model. Such an estimate is possible because the observations include the effects of UHI, whereas the model used does not include urban effects. Therefore, the errors in the simulated surface air temperature, defined as the difference between simulated and observed temperatures (simulated minus observed), are negative in urban areas but 0 in rural areas. UHI intensity is estimated by calculating the difference in temperature error between urban and rural areas. Our results indicate that overall UHI intensity in Japan is 1.5 K and that the intensity is greater in nighttime than in daytime, consistent with the previous studies. This study also shows that root mean square error and the magnitude of systematic error for the annual mean temperature are small (within 1.0 K).     

Retrieval of Sea Surface Wind Speed by One-Dimensional Synthetic Aperture Microwave Radiometer

One-dimensional synthetic aperture microwave radiometers have higher spatial resolution and record measurements at multiple incidence angles. In this paper, we propose a multiple linear regression method to retrieve sea surface wind speed at an incidence angle between 0° ~65°. We assume that a one-dimensional synthetic aperture microwave radiometer operates at frequencies of 6.9, 10.65, 18.7, 23.8 and 36.5 GHz. Then, the microwave radiative transfer forward model is used to simulate the measured brightness temperatures. The sensitivity of the brightness temperatures at 0°~65° to the sea surface wind speed is calculated. Then, vertical polarization channels(VR), horizontal polarization channels(HR) and all channels(AR) are used to retrieve the sea surface wind speed via a multiple linear regression algorithm at 0° ~65°, and the relationship between the retrieval error and incidence angle is obtained. The results are as follows:(1) The sensitivity of the vertical polarization brightness temperature to the sea surface wind speed is smaller than that of the horizontal polarization.(2) The retrieval error increases with Gaussian noise. The retrieval error of VR first increases and then decreases with increasing incidence angle, the retrieval error of HR gradually decreases with increasing incidence angle, and the retrieval error of AR first decreases and then increases with increasing incidence angle.(3) The retrieval error of AR is the lowest and it is necessary to retrieve the sea surface wind speed at a larger incidence angle for AR.     

The contribution of urbanization to recent extreme heat events and a potential mitigation strategy in the Beijing–Tianjin–Hebei metropolitan area

This paper addresses the contribution of urban land use change to near-surface air temperature during the summer extreme heat events of the early twenty-first century in the Beijing–Tianjin–Hebei metropolitan area. This study uses the Weather Research Forecasting model with a single urban canopy model and the newest actual urban cover datasets. The results show that urban land use characteristics that have evolved over the past ~20 years in the Beijing–Tianjin–Hebei metropolitan area have had a significant impact on the extreme temperatures occurring during extreme heat events. Simulations show that new urban development has caused an intensification and expansion of the areas experiencing extreme heat waves with an average increase in temperature of approximately 0.60 °C. This change is most obvious at night with an increase up to 0.95 °C, for which the total contribution of anthropogenic heat is 34 %. We also simulate the effects of geo-engineering strategies increasing the albedo of urban roofs, an effective way of reducing urban heat island, which can reduce the urban mean temperature by approximately 0.51 °C and counter approximately 80 % of the heat wave results from urban sprawl during the last 20 years.     

Effects of Roof-Edge Roughness on Air Temperature and Pollutant Concentration in Urban Canyons

The influence of roof-edge roughness elements on airflow, heat transfer, and street-level pollutant transport inside and above a two-dimensional urban canyon is analyzed using an urban energy balance model coupled to a large-eddy simulation model. Simulations are performed for cold (early morning) and hot (mid afternoon) periods during the hottest month of the year (August) for the climate of Abu Dhabi, United Arab Emirates. The analysis suggests that early in the morning, and when the tallest roughness elements are implemented, the temperature above the street level increases on average by 0.5 K, while the pollutant concentration decreases by 2% of the street-level concentration. For the same conditions in mid afternoon, the temperature decreases conservatively by 1 K, while the pollutant concentration increases by 7% of the street-level concentration. As a passive or active architectural solution, the roof roughness element shows promise for improving thermal comfort and air quality in the canyon for specific times, but this should be further verified experimentally. The results also warrant a closer look at the effects of mid-range roughness elements in the urban morphology on atmospheric dynamics so as to improve parametrizations in mesoscale modelling.     

Modeling the climatic effects of urbanization in the Beijing–Tianjin–Hebei metropolitan area

In this analysis, the weather research and forecasting model coupled with a single-layer urban canopy model is used to simulate the climatic impacts of urbanization in the Beijing–Tianjin–Hebei metropolitan area, which has experienced significant expansion in its urban areas. Two cases examining current landscapes and the sensitivity test of urban areas replaced by cropland have been carried out to explore the changes in the surface air and atmospheric boundary structure. The impact of urbanization on annual mean surface air temperature has been found to be more than 1 °C in urban areas, and the maximum difference is almost 2 °C. The change in near-surface level temperature is most pronounced in winter, but the area influenced by urbanization is slightly larger in summer. The annual mean water vapor mixing ratio and wind speed are both reduced in the urban area. The effect of urbanization can only heat the temperature inside the urban boundary layer, below 850 hPa. The modeling results also indicate that the underlying surface thermal forces induced by the “urban heat island” effect enhance vertical air movement and engenders a convergence zone over urban areas. The convergence at low level together with the moisture increases in the layer between 850 and 700 hPa triggered the increase of convective precipitation.     

Psychrometric apparatus for Bowen-ratio determination over forests

The psychrometric apparatus design for Bowen ratio determination reported previously by Sargeant and Tanner was modified and a new apparatus built. Modification of the intake design improved the symmetry and rigidity of the sensor mounting. Wet- and dry-bulb differences were measured with an error less than 0.01 °C over a vertical distance of 1 m. Continuous measurements of the Bowen ratio over a 7.8-m Douglas fir forest were made for 6 weeks. An example of the energy balance for the forest for one day using this equipment is reported.     

Basic analysis of climate and urban bioclimate of Dar es Salaam, Tanzania

Better understanding of urban microclimate and bioclimate of any city is imperative today when the world is constrained by both urbanisation and global climate change. Urbanisation generally triggers changes in land cover and hence influencing the urban local climate. Dar es Salaam city in Tanzania is one of the fast growing cities. Assessment of its urban climate and the human biometeorological conditions was done using the easily available synoptic meteorological data covering the period 2001–2011. In particular, the physiologically equivalent temperature (PET) was calculated using the RayMan software and results reveal that the afternoon period from December to February (DJF season) is relatively the most thermal stressful period to human beings in Dar es Salaam where PET values of above 35 °C were found. Additionally, the diurnal cycle of the individual meteorological elements that influence the PET index were analysed and found that air temperature of 30–35 °C dominate the afternoon period from 12:00 to 15:00 hours local standard time at about 60 % of occurrence. The current results, though considered as preliminary to the ongoing urban climate study in the city, provide an insight on how urban climate research is of significant importance in providing useful climatic information for ensuring quality of life and wellbeing of city dwellers.     

Radiative surface temperature and energy balance of a wheat canopy

The sensible heat loss from a stand of winter wheat was calculated from radiometric measurements of crop surface temperature, measurements of air temperature, and an atmospheric resistance to momentum transfer; corresponding latent heat flux was obtained through the energy balance equation. These estimates of sensible and latent heat were compared with fluxes from the Bowen Ratio method. When radiative temperature was derived using a measured canopy emissivity of 0.98, calculations of sensible heat flux were systematically 50–100 W m^-2 less than Bowen Ratio values. The two techniques agreed more closely when an apparent emissivity of 0.96 was used with an apparent reflectivity of 0.03. The mean difference between the estimates of latent heat flux was then -16 ± 32 W m^-2.The surface temperature method showed less systematic error in comparison with the Bowen Ratio values than did estimates using the aerodynamic method.On leave from: University of Nottingham, School of Agriculture, Loughborough LE12 5RD.     

Effects of the large-scale atmospheric circulation on the onset and strength of urban heat islands: a case study

Air temperature was monitored at 13 sites across the urban perimeter of a Brazilian midsize city in winter 2011. In this study, we show that the urban heat island (UHI) develops only at night and under certain weather conditions, and its intensity depends not only on the site's land cover but also on the meteorological setting. The urban heat island intensity was largest (6.6 °C) under lingering high-pressure conditions, milder (3.0 °C) under cold anticyclones and almost vanished (1.0 °C) during the passage of cold fronts. The cooling rates were calculated to monitor the growth and decay of the UHI over each specific synoptic setting. Over four contiguous days under the effect of a lingering high-pressure event, we observed that the onset of cooling was always at about 2 h before sunset. The reference site attained mean cooling rate of ?2.6 °C h^?1 at sunset, whilst the maximum urban rate was ?1.2 °C h^?1. Under a 3-day cold anticyclone episode, cooling also started about 2 h before sunset, and the difference between maximum rural (?2.0 °C h^?1) and urban (?1.0 °C h^?1) cooling rates diminished. Under cold-front conditions, the cooling rate was homogeneous for all sites and swang about zero throughout the day. The air temperature has a memory effect under lingering high-pressure conditions which intensified the UHI, in addition to the larger heat storage in the urban area. Cold anticyclone conditions promoted the development of the UHI; however, the cold air pool and relatively light winds smoothed out its intensity. Under the influence of cold fronts, the urban fabric had little effect on the city's air temperature field, and the UHI was imperceptible.     

Using urban effect corrected temperature data and a tree phenology model to project geographical shift of cherry flowering date in South Korea

Temperate zone deciduous tree phenology may be vulnerable to projected temperature change, and associated geographical impact is of concern to ecologists. Although many phenology models have been introduced to evaluate climate change impact, there has been little attempt to show the spatial variation across a geographical region due to contamination by the urban heat island (UHI) effect as well as the insufficient spatial resolution of temperature data. We present a practical method for assessing climate change impact on tree phenology at spatial scales sufficient to accommodate the UHI effect. A thermal time-based two-step phenological model was adapted to simulate and project flowering dates of Japanese cherry (Prunus serrulata var. spontanea) in South Korea under the changing climates. The model consists of two sequential periods: the rest period described by chilling requirements and the forcing period described by heating requirements. Daily maximum and minimum temperature are used to calculate daily chill units until a pre-determined chilling requirement for rest release is met. After the projected rest release date, daily heat units (growing degree days) are accumulated until a pre-determined heating requirement for flowering is achieved. Model parameters were derived from the observed bud-burst and flowering dates of cherry tree at the Seoul station of the Korea Meteorological Administration (KMA), along with daily temperature data for 1923–1948. The model was validated using the observed data at 18 locations across South Korea during 1955–2004 with a root mean square error of 5.1 days. This model was used to project flowering dates of Japanese cherry in South Korea from 1941 to 2100. Gridded data sets of daily maximum and minimum temperature with a 270 m grid spacing were prepared for the climatological normal years 1941–1970 and 1971–2000 based on observations at 56 KMA stations and a geospatial interpolation scheme for correcting urban heat island effect as well as elevation effect. We obtained a 25 km-resolution, 2011–2100 temperature projection data set covering peninsular Korea under the auspices of the Inter-governmental Panel on Climate Change—Special Report on Emission Scenarios A2 from the Meteorological Research Institute of KMA. The data set was converted to 270 m gridded data for the climatological years 2011–2040, 2041–2070 and 2071–2100. The phenology model was run by the gridded daily maximum and minimum temperature data sets, each representing climatological normal years for 1941–1970, 1971–2000, 2011–2040, 2041–2070, and 2071–2100. According to the model calculation, the spatially averaged flowering date for the 1971–2000 normal is earlier than that for 1941–1970 by 5.2 days. Compared with the current normal (1971–2000), flowering of Japanese cherry is expected to be earlier by 9, 21, and 29 days in the future normal years 2011–2040, 2041–2070, and 2071–2100, respectively. Southern coastal areas might experience springs with incomplete or even no flowering caused by insufficient chilling required for breaking bud dormancy.     

基于一维变分算法的红外高光谱(IASI)卫星遥感大气温湿廓线研究

大气温湿度廓线是大气重要参数,在数值天气预报及天气预警中具有重要的应用价值。为获得高精度的大气温度与水汽混合比廓线数据,研究了基于Metop-A/IASI红外高光谱资料的大气温度与水汽混合比廓线变分反演方法。利用IASI高光谱传感器温度和水汽探测通道资料,结合CRTM模式和WRF模式预报技术,使用一维变分方法,研究了卫星资料质量控制、背景误差协方差本地化、观测误差协方差计算等方法,构建了大气温度及水汽混合比廓线变分反演系统,并在北京、青岛、沈阳3个地区开展了反演试验。以探空为标准的反演结果对比显示,使用WRF模式预报值作为背景场,温度的平均误差绝对值小于0.6 K,均方根误差为0.89 K;水汽混合比的平均误差绝对值小于0.021 g/kg,均方根误差为0.02 g/kg。试验结果表明:基于一维变分方法,可以利用Metop-A/IASI红外高光谱资料进行大气温度与水汽混合比廓线高精度探测。     

Spatiotemporal modeling of monthly soil temperature using artificial neural networks

Soil temperature data are critical for understanding land–atmosphere interactions. However, in many cases, they are limited at both spatial and temporal scales. In the current study, an attempt was made to predict monthly mean soil temperature at a depth of 10 cm using artificial neural networks (ANNs) over a large region with complex terrain. Gridded independent variables, including latitude, longitude, elevation, topographic wetness index, and normalized difference vegetation index, were derived from a digital elevation model and remote sensing images with a resolution of 1 km. The good performance and robustness of the proposed ANNs were demonstrated by comparisons with multiple linear regressions. On average, the developed ANNs presented a relative improvement of about 44 % in root mean square error, 70 % in mean absolute percentage error, and 18 % in coefficient of determination over classical linear models. The proposed ANN models were then applied to predict soil temperatures at unsampled locations across the study area. Spatiotemporal variability of soil temperature was investigated based on the obtained database. Future work will be needed to test the applicability of ANNs for estimating soil temperature at finer scales.     

Retrieving air humidity,global solar radiation,and reference evapotranspiration from daily temperatures: development and validation of new methods for Mexico. Part II: radiation

We propose a new model to estimate daily global radiation from daily temperature range measurements. This model combines that of Majumdar et al. (Sol Energy 13(4):383–394, 1972) to estimate clear sky radiation with a Gompertz function to estimate the relation between temperature range and cloud transmittance. Model parameters are estimated from historical weather data: maximum and minimum temperatures and, if available, relative humidity; no other calibration is required. The model was parametrized and validated using 788 weather stations in Mexico. When calibrated using historical humidity data, daily global radiation was estimated with a mean root mean square error of 3.06 MJ m^?2 day^?1. The model performed well in all situations, except for a few stations around the Gulf of Mexico and in mountain areas. When using estimated humidity, the root mean square error of prediction was only slightly degraded (3.07 MJ m^?2 day^?1). Possible theoretical basis and applicability of this model to other environments are discussed.     

The July urban heat island of Bucharest as derived from modis images

The urban heat island (UHI) of the city of Bucharest (Romania) is analyzed in terms of its extension, geometry, and magnitude using the surface thermal data provided by the moderate resolution imaging spectroradiometer (MODIS) sensors. An objective method is developed that allows to delineate the UHI. The study focuses on the months of July from the 2000–2006 time interval. The average surface temperatures obtained for each pixel (1 km resolution) were analyzed on cross-profiles that helped us to determine the outline of the UHI. The shifting points identified by the Rodionov test in the temperature series of each profile were considered as possible limits of the UHI. Seemingly, the land cover has a major influence on the extension and the geometry of the Bucharest UHI in July. The magnitude of the heat island was calculated by comparing the average temperature inside its limits and the average temperature of the 5 km (a) and of the 10 km (b) buffers around it. The thermal difference between the UHI and the surrounding area of Bucharest is higher and more variable during the daytime, and is noticeably related to the land cover.     

Estimation of turbulent sensible heat and momentum fluxes over a heterogeneous urban area using a large aperture scintillometer

The accurate determination of surface-layer turbulent fluxes over urban areas is critical to understanding urban boundary layer (UBL) evolution. In this study, a remote-sensing technique using a large aperture scintillometer (LAS) was investigated to estimate surface-layer turbulent fluxes over a highly heterogeneous urban area. The LAS system, with an optical path length of 2.1 km, was deployed in an urban area characterized by a complicated land-use mix (residential houses, water body, bare ground, etc.). The turbulent sensible heat (Q H) and momentum fluxes (τ) were estimated from the scintillation measurements obtained from the LAS system during the cold season. Three-dimensional LAS footprint modeling was introduced to identify the source areas ("footprint") of the estimated turbulent fluxes. The analysis results showed that the LAS-derived turbulent fluxes for the highly heterogeneous urban area revealed reasonable temporal variation during daytime on clear days, in comparison to the land-surface process-resolving numerical modeling. A series of sensitivity tests indicated that the overall uncertainty in the LAS-derived daytime Q H was within 20%-30% in terms of the influence of input parameters and the non-dimensional similarity function for the temperature structure function parameter, while the estimation errors in τ were less sensitive to the factors of influence, except aerodynamic roughness length. The 3D LAS footprint modeling characterized the source areas of the LAS-derived turbulent fluxes in the heterogeneous urban area, revealing that the representative spatial scales of the LAS system deployed with the 2.1 km optical path distance ranged from 0.2 to 2 km2 (a "micro-α scale"), depending on local meteorological conditions.     

Spatio-temporal prediction of daily temperatures using time-series of MODIS LST images

A computational framework to generate daily temperature maps using time-series of publicly available MODIS MOD11A2 product Land Surface Temperature (LST) images (1 km resolution; 8-day composites) is illustrated using temperature measurements from the national network of meteorological stations (159) in Croatia. The input data set contains 57,282 ground measurements of daily temperature for the year 2008. Temperature was modeled as a function of latitude, longitude, distance from the sea, elevation, time, insolation, and the MODIS LST images. The original rasters were first converted to principal components to reduce noise and filter missing pixels in the LST images. The residual were next analyzed for spatio-temporal auto-correlation; sum-metric separable variograms were fitted to account for zonal and geometric space-time anisotropy. The final predictions were generated for time-slices of a 3D space-time cube, constructed in the R environment for statistical computing. The results show that the space-time regression model can explain a significant part of the variation in station-data (84%). MODIS LST 8-day (cloud-free) images are unbiased estimator of the daily temperature, but with relatively low precision (±4.1°C); however their added value is that they systematically improve detection of local changes in land surface temperature due to local meteorological conditions and/or active heat sources (urban areas, land cover classes). The results of 10–fold cross-validation show that use of spatio-temporal regression-kriging and incorporation of time-series of remote sensing images leads to significantly more accurate maps of temperature than if plain spatial techniques were used. The average (global) accuracy of mapping temperature was ±2.4°C. The regression-kriging explained 91% of variability in daily temperatures, compared to 44% for ordinary kriging. Further software advancement—interactive space-time variogram exploration and automated retrieval, resampling and filtering of MODIS images—are anticipated.     

Thermal bioclimate in idealized urban street canyons in Campinas, Brazil

Among several urban design parameters, the height-to-width ratio (H/W) and orientation are important parameters strongly affecting thermal conditions in cities. This paper quantifies changes in thermal comfort due to typical urban canyon configurations in Campinas, Brazil, and presents urban guidelines concerning H/W ratios and green spaces to adapt urban climate change. The study focuses on thermal comfort issues of humans in urban areas and performs evaluation in terms of physiologically equivalent temperature (PET), based on long-term data. Meteorological data of air temperature, relative humidity, wind speed and solar radiation over a 7-year period (2003–2010) were used. A 3D street canyon model was designed with RayMan Pro software to simulate the influence of urban configuration on urban thermal climate. The following configurations and setups were used. The model canyon was 500 m in length, with widths 9, 21, and 44 m. Its height varied in steps of 2.5 m, from 5 to 40 m. The canyon could be rotated in steps of 15°. The results show that urban design parameters such as width, height, and orientation modify thermal conditions within street canyons. A northeast–southwest orientation can reduce PET during daytime more than other scenarios. Forestry management and green areas are recommended to promote shade on pedestrian areas and on façades, and to improve bioclimate thermal stress, in particular for H/W ratio less than 0.5. The method and results can be applied by architects and urban planners interested in developing responsive guidelines for urban climate issues.     

The extent and intensity of the urban heat island in Iași city,Romania

The study underlines the characteristics of the urban heat island of Ia?i (Ia?i’s UHI) on the basis of 3 years of air temperature measurements obtained by fixed-point observations. We focus on the identification of UHI development and intensity as it is expressed by the temperature differences between the city centre and the rural surroundings. Annual, seasonal and daily characteristics of Ia?i’s UHI are investigated at the level of the classical weather observation. In brief, an intensity of 0.8 °C of UHI and a spatial extension which corresponds to the densely built area of the city were delineated. The Ia?i UHI is stronger during summer calm nights—when the inner city is warmer with 2.5–3 °C than the surroundings—and is weaker during windy spring days. The specific features of Ia?i’s UHI bear a profound connection to the specificity of the urban structure, the high atmospheric stability in the region and the local topography. Also, the effects of Ia?i’s UHI upon some environmental aspects are presented as study cases. For instance, under the direct influence of UHI, we have observed that in the city centre, the apricot tree blossoms earlier (with up to 4 days) and the depth of the snow cover is significantly lower (with up to 10 cm for a rural snow depth of 30 cm) than in the surrounding areas.     

Climate-induced changes in river water temperature in North Iberian Peninsula

With the surface air temperature (SAT) data at 37 stations on Central Yunnan Plateau (CYP) for 1961–2010 and the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data, the temporal-spatial patterns of the SAT trends are detected using Sen’s Nonparametric Estimator of Slope approach and MK test, and the impact of urbanization on surface warming is analyzed by comparing the differences between the air temperature change trends of urban stations and their corresponding rural stations. Results indicated that annual mean air temperature showed a significant warming trend, which is equivalent to a rate of 0.17 °C/decade during the past 50 years. Seasonal mean air temperature presents a rising trend, and the trend was more significant in winter (0.31 °C/decade) than in other seasons. Annual/seasonal mean air temperature tends to increase in most areas, and higher warming trend appeared in urban areas, notably in Kunming city. The regional mean air temperature series was significantly impacted by urban warming, and the urbanization-induced warming contributed to approximately 32.3–62.9 % of the total regional warming during the past 50 years. Meantime, the urbanization-induced warming trend in winter and spring was more significant than that in summer and autumn. Since 1985, the urban heat island (UHI) intensity has gradually increased. And the urban temperatures always rise faster than rural temperatures on the CYP.