Storage Heat Flux Research Articles

Measurements and simulations of energy fluxes over a high-rise and compact urban area in Hong Kong

Measuring energy fluxes in a dense and high-rise urban area is extremely challenging, thus our knowledge in such area remains limited. This study assessed the surface energy fluxes and investigated the energy balance closure (EBC) over such complex urban surface in Hong Kong. Net radiation (QN), sensible (QH) and latent (QE) heat fluxes were measured using an eddy covariance system from September 2018 to August 2019. Anthropogenic heat flux (QF) was simulated by a large-scale urban energy model (i.e., LUCY) and validated by an anthropogenic heat database (i.e., AHE_KL). Storage heat flux (QS) was estimated by an objective hysteresis model (OHM). Among five energy terms, QF showed the largest values of around 750 Wm−2 especially in the afternoon. Whereas, QE varying within 150 Wm−2 showed the smallest values. The variation range of net radiation, sensible heat flux and storage heat was respectively from −50 to 600, 0 to 450 and −30 to 300 W m−2. EBC generally showed a negative relationship with surface heterogeneity. Best EBC was observed in the direction with a relatively constant and large aspect ratio, and with the most occurrence of unstable stratifications. The uncertainties of QH and QE fluxes were respectively estimated to be approximately 8% and 7%. The result of LUCY was consistent with that of AHE_KL. EBC was not sensitive to different coefficients estimating QS. This study helped to fill a gap in our understanding of surface energy and turbulent fluxes in compact cities with high-rise buildings and shed insights into the future installation of eddy covariance tower in similar areas. The required height of the eddy covariance tower in such urban sites might not be as restrictive as that in other urban areas with low-rise buildings or with low building density, thus making it more feasible to set up such observation towers.

Interaction between heat wave and urban heat island: A case study in a tropical coastal city, Singapore

Heat waves are unusually high temperature events over consecutive days and may cause adverse impacts such as morbidity and mortality. The interaction between heat waves and urban heat island (UHI) effects has remained a subject of debate, as some studies prove heat wave-UHI synergy while others do not. Furthermore, heat waves affect tropical cities more severely than mid-latitude cities, but there is a disproportionate lack of heat wave studies focusing on tropical cities. We attempt to narrow this gap by studying the heat wave in Singapore in April 2016 using ground observations and the Weather Research and Forecasting (WRF) model. Compared to non-heat wave days, the ground observations show that daytime temperatures can be 3 °C higher during the heat wave. Despite the temperature spike, the UHI intensity is not amplified during the heat wave, maintaining its peak near 2.5 °C during both heat wave and non-heat wave periods. WRF simulation results also agree well with measurements and predict UHI peaks near 2.5 °C during both periods, showing no heat wave-UHI synergy. The spatially averaged UHI intensity also shows no such synergy. There is no significant change of wind speed, soil moisture availability or heat storage flux during the heat wave. Therefore, the lack of heat wave-UHI synergy in our study is consistent with current understanding of factors contributing to UHI. This study shows that the heat wave-UHI interaction in a tropical city can be different from that in cities in the temperate climate zone and more studies should be conducted in tropical cities, which are projected to suffer larger impacts of increasing heat stress.

Urban storage heat flux variability explored using satellite, meteorological and geodata

The storage heat flux (ΔQS) is the net flow of heat stored within a volume that may include the air, trees, buildings and ground. Given the difficulty of measurement of this important and large flux in urban areas, we explore the use of Earth Observation (EO) data. EO surface temperatures are used with ground-based meteorological forcing, urban morphology, land cover and land use information to estimate spatial variations of ΔQS in urban areas using the Element Surface Temperature Method (ESTM). First, we evaluate ESTM for four “simpler” surfaces. These have good agreement with observed values. ESTM coupled to SUEWS (an urban land surface model) is applied to three European cities (Basel, Heraklion, London), allowing EO data to enhance the exploration of the spatial variability in ΔQS. The impervious surfaces (paved and buildings) contribute most to ΔQS. Building wall area seems to explain variation of ΔQS most consistently. As the paved fraction increases up to 0.4, there is a clear increase in ΔQS. With a larger paved fraction, the fraction of buildings and wall area is lower which reduces the high values of ΔQS.

Local-Scale Urban Energy Balance Observation under Various Sky Conditions in a Humid Subtropical Region

AbstractThe present study presents local-scale urban energy balance observations under various sky conditions in a humid subtropical region. The study site is a typical urban residential area in Guangzhou in which building density is 38%, vegetation coverage is 36%, and mean building height is 21 m. The observation was conducted at a 110-m-high tower using the eddy covariance technique from September to November 2016. The median diurnal pattern and daily maxima were achieved for all radiation components and turbulent fluxes. The Bowen ratio (β) results indicated a predominant role for sensible heat flux (QH) in the daytime and latent heat flux (QE) at night. The sky conditions played a significant part in the urban surface energy exchanges, showing that the median daily maxima of net radiation (Q*), QH, storage heat flux (ΔQS), surface albedo, and β all present a consistent order from large to small for clear, cloudy, and rainy days and a different order of rainy, clear, and cloudy days for QE. The mean daytime QH/Q*, QE/Q*, ΔQS/Q*, and β changed with urban density, while QE/Q* and β also varied with vegetation fraction. Furthermore, the adaptability of net all-wave radiation parameterization (NARP), objective hysteresis model (OHM), and local-scale urban meteorological parameterization scheme (LUMPS) were validated, given the index of agreements of 0.998 and 0.951 for Q* and ΔQS and the reasonable RMSEs for QH and QE. The present study helps to verify and improve the parameterizations of energy exchange over an urban surface in the humid subtropical region.

Impacts of future urban expansion on urban heat island effects during heatwave events in the city of Melbourne in southeast Australia

AbstractThe city of Melbourne in southeast Australia is planning to expand urban areas substantially by the year 2050 and this expansion has the potential to alter the Urban Heat Island (UHI), that is, higher temperatures in urban areas as compared to surrounding rural areas. Moreover, Melbourne has been experiencing more frequent heatwaves for last two decades, and the intensity and duration of heatwaves is expected to increase in the future, which could exacerbate the UHI. This study evaluates the potential impacts of future urban expansion on the urban meteorology in Melbourne city during four of the most severe heatwave events during the period 2000–2009. Urban expansion is implemented as high‐density urban with a high urban fraction of 0.9 to investigate the maximum possible impact. Simulations are carried out using the Weather Research and Forecasting model coupled with the Single‐Layer Urban Canopy Model with current land‐use and future urban expansion scenarios. Urban expansion increases the near‐surface (2‐m) UHI (UHI2) by 0.75 to 2.80 °C and the skin‐surface UHI (UHIsk) by 1.9 to 5.4 °C over the expanded urban areas during the night, with no changes in existing urban areas. No substantial changes in UHI2 and UHIsk occur during the day over both existing and expanded urban areas. This is largely driven by changes in the storage heat flux, with an increase in storage heat at night and a decrease during the day; that is, excess storage heat accumulated during the day is released at night, which causes a slower decrease of near‐surface temperature and increase in the UHI. Urban expansion did not affect human thermal comfort (HTC) in existing urban areas and there were no marked differences in HTC between existing and expanded urban areas.

Effectiveness of vegetated patches as Green Infrastructure in mitigating Urban Heat Island effects during a heatwave event in the city of Melbourne

The city of Melbourne in southeast Australia experiences frequent heatwaves and their frequency, intensity and duration are expected to increase in the future. In addition, Melbourne is the fastest growing city in Australia and experiencing rapid urban expansion. Heatwaves and urbanization contribute in intensifying the Urban Heat Island (UHI) effect, i.e., higher temperatures in urban areas as compared to surrounding rural areas. The combined effects of UHI and heatwaves have substantial impacts on the urban environment, meteorology and human health, and there is, therefore, a pressing need to investigate the effectiveness of different mitigation options. This study evaluates the effectiveness of urban vegetation patches such as mixed forest (MF), combination of mixed forest and grasslands (MFAG), and combination of mixed shrublands and grasslands (MSAG) in reducing UHI effects in the city of Melbourne during one of the most severe heatwave events. Simulations are carried out by using the Weather Research and Forecasting (WRF) model coupled with the Single Layer Urban Canopy Model (SLUCM). The fractions of vegetated patches per grid cell are increased by 20%, 30%, 40% and 50% using the mosaic method of the WRF model. Results show that by increasing fractions from 20 to 50%, MF reduces near surface (2 m) UHI (UHI2) by 0.6–3.4 °C, MSAG by 0.4–3.0 °C, and MFAG by 0.6–3.7 °C during the night, but there was no cooling effect for near surface temperature during the hottest part of the day. The night-time cooling was driven by a reduction in storage heat. Vegetated patches partitioned more net radiation into latent heat flux via evapotranspiration, with little to no change in sensible heat flux, but rather, a reduction in the storage heat flux during the day. Since the UHI is driven by the release of stored heat during the night, the reduced storage heat flux results in reductions in the UHI. The reductions of the UHI2 varied non-linearly with the increasing vegetated fractions, with lager fractions of up to 50% resulting in substantially larger reductions. MF and MFAG were more effective in reducing UHI2 as compared to MSAG. Vegetated patches were not effective in improving HTC during the day, but a substantial improvement of HTC was obtained between the evening and early morning particularly at 2100 local time, when the thermal stress changes from strong to moderate. Although limited to a single heatwave event and city, this study highlights the maximum potential benefits of using vegetated patches in mitigating the UHI during heatwaves and the overall principles are applicable elsewhere.

Heat transfer enhancement of charging and discharging of phase change materials and size optimization of a latent thermal energy storage system for solar cold storage application

Abstract In this work, phase change material (PCM) is considered as thermal energy backup system for solar cold storage applications when there is peak power demand or power failure or no sun shines situations. A numerical study of solidification (charging) and melting (discharging) of PCM validated by experimental data is performed to explore the performance of a unique latent heat thermal energy storage (LHTES) system. The LHTES unit (PCM pack) occupied with PCM acts as a heat exchanger made up from evaporator tube along with rectangular metal fins which enhance the heat transfer during phase changing of PCM. Evaporator with 5, 8, 10, and 12 longitudinal aluminum fins, and without fin inside the PCM pack of six different thicknesses (4.5 cm, 5.0 cm 5.5 cm, 6.0 cm, 6.5 cm, and 7.0 cm) are considered to investigate the charging and discharging characteristics of PCM in our present study. To obtain the best performance from the PCM pack, heat transfer characteristics and temperature distributions of PCM, and the effect of variation of thickness of the PCM pack are studied through computational fluid dynamics (CFD) simulation. Solidification and melting model of ANSYS Fluent 15.0 package employing enthalpy-porosity technique is used to develop 3-D simulation models. Faster solidification, as well as a higher energy storage capacity and heat flux during melting is found for the PCM pack of 6.5 cm thickness with higher number of fins. A lab scale experimental set-up is fabricated to compare the present simulation results which shows reasonably well validation during both the charging and discharging.

Integrating Urban Form, Function, and Energy Fluxes in a Heat Exposure Indicator in View of Intra-Urban Heat Island Assessment and Climate Change Adaptation

Cities worldwide are getting warmer due to the combined effects of urban heat and climate change. To this end, local policy makers need to identify the most thermally vulnerable areas within cities. The Local Climate Zone (LCZ) scheme highlights local-scale variations; however, its classes, although highly valuable, are to a certain extent generalized in order to be universally applicable. High spatial resolution indicators have the potential to better reflect city-specific challenges; in this paper, the Urban Heat Exposure (UHeatEx) indicator is developed, integrating the physical processes that drive the urban heat island (UHI). In particular, the urban form is modeled using remote sensing and geographical information system (GIS) techniques, and used to estimate the canyon aspect ratio and the storage heat flux. The Bowen ratio is calculated using the aerodynamic resistance methodology and downscaled remotely sensed surface temperatures. The anthropogenic heat flux is estimated via a synergy of top–down and bottom–up inventory approaches. UHeatEx is applied to the city of Athens, Greece; it is correlated to air temperature measurements and compared to the LCZs classification. The results reveal that UHeatEx has the capacity to better reflect the strong intra-urban variability of the thermal environment in Athens, and thus can be supportive for adaptation responses. High-resolution climate projections from the EURO-CORDEX ensemble for the region show that the adverse effects of the existing thermal inequity are expected to worsen in the coming decades.

Evaluation of urban surface parameterizations in WRF model using energy fluxes measurements in Portugal

The performance of WRF model was investigated for the simulation of urban microclimate, with particular focus on energy fluxes, using different urban surface parameterizations. The model performance was evaluated using measurements carried out between August and December 2014 in Portugal. Several simulations were performed over two different areas, Porto urban area and Aveiro suburban area, for the entire measurement period. Distinct simulations were performed using different urban parametrizations: (i) the Noah Land Surface Model (LSM); (ii) a single-layer urban canopy model (UCM); and (iii) a modelling system composed by WRF and SUEWS models (WRF-SUEWS).The results showed that both UCM and SUEWS are able to simulate the energy partitioning over the low and high intensity residential. At the low intensity residential area, the majority of energy is partitioned to latent heat flux, accounting on average for 47% and 49% of the daytime available energy, for UCM and SUEWS, respectively. At the high intensity residential area, the greatest share of energy goes to sensible heat flux (42% [UCM] and 50% [SUEWS]), followed by the storage heat flux (33% [UCM] and 43% [SUEWS]). For both areas, a completely different energy partitioning was obtained when the LSM was used. The analysis performed showed that the UCM are able to provide a more accurate turbulent energy partitioning (sensible and latent heat), which contribute to enhance the urban microclimate simulation results; the systematic model biases in the LSM simulation was reduced by 1–2 °C in air temperature and by 0.5–1 m s−1 in wind speeds at near surface layer, on average, depending on the urban density. The overall results suggest that an appropriate representation of urban physical processes are crucial to improve numerical tools suited for the modelling of the urban atmospheric boundary layer.

Evaluation of the Surface Urban Energy and Water Balance Scheme (SUEWS) at a Dense Urban Site in Shanghai: Sensitivity to Anthropogenic Heat and Irrigation

Abstract The Surface Urban Energy and Water Balance Scheme (SUEWS) is used to investigate the impact of anthropogenic heat flux QF and irrigation on surface energy balance partitioning in a central business district of Shanghai. Diurnal profiles of QF are carefully derived based on city-specific hourly electricity consumption data, hourly traffic data, and dynamic population density. The QF is estimated to be largest in summer (mean daily peak 236 W m−2). When QF is omitted, the SUEWS sensible heat flux QH reproduces the observed diurnal pattern generally well, but the magnitude is underestimated compared to observations for all seasons. When QF is included, the QH estimates are improved in spring, summer, and autumn but are poorer in winter, indicating winter QF is overestimated. Inclusion of QF has little influence on the simulated latent heat flux QE but improves the storage heat flux estimates except in winter. Irrigation, both amount and frequency, has a large impact on QE. When irrigation is not considered, the simulated QE is underestimated for all seasons. The mean summer daytime QE is largely overestimated compared to observations under continuous irrigation conditions. Model results are improved when irrigation occurs with a 3-day frequency, especially in summer. Results are consistent with observed monthly outdoor water use. This study highlights the importance of appropriately including QF and irrigation in urban land surface models—terms not generally considered in many previous studies.

A New Model to Downscale Urban and Rural Surface and Air Temperatures Evaluated in Shanghai, China

AbstractA simple model, the Surface Temperature and Near-Surface Air Temperature (at 2 m) Model (TsT2m), is developed to downscale numerical model output (such as from ECMWF) to obtain higher-temporal- and higher-spatial-resolution surface and near-surface air temperature. It is evaluated in Shanghai, China. Surface temperature (Ts) and near-surface air temperature (Ta) submodels account for variations in land cover and their different thermal properties, resulting in spatial variations of surface and air temperature. The net all-wave radiation parameterization (NARP) scheme is used to compute net wave radiation for the surface temperature submodel, the objective hysteresis model (OHM) is used to calculate the net storage heat fluxes, and the surface temperature is obtained by the force-restore method. The near-surface air temperature submodel considers the horizontal and vertical energy changes for a column of well-mixed air above the surface. Modeled surface temperatures reproduce the general pattern of MODIS images well, while providing more detailed patterns of the surface urban heat island. However, the simulated surface temperatures capture the warmer urban land cover and are 10.3°C warmer on average than those derived from the coarser MODIS data. For other land-cover types, values are more similar. Downscaled, higher-temporal- and higher-spatial-resolution air temperatures are compared to observations at 110 automatic weather stations across Shanghai. After downscaling with TsT2m, the average forecast accuracy of near-surface air temperature is improved by about 20%. The scheme developed has considerable potential for prediction and mitigation of urban climate conditions, particularly for weather and climate services related to heat stress.

Hotterdam: Mapping the social, morphological, and land-use dimensions of the Rotterdam urban heat island

Climate scientists forecast that heat waves will occur more often in the Netherlands in the coming decades. The Hotterdam study accordingly measured urban heat and modelled the surface energy balance in the Dutch city of Rotterdam. It identified in detail the city’s social, morphological, and land-use dimensions using a geographic information system (GIS), 3D models, and satellite images. It used hierarchical and multivariate regression analyses to determine the links between temperatures and the surface energy balance on the one hand, and social, morphological, and land-use aspects on the other. The Hotterdam study did establish a link between the urban heat island effect in Rotterdam and the health of its population. It also statistically explained the high rate of mortality among seniors seventy-five and over during the summer of 2006. The spatial concentration of senior citizens, the average age of the buildings they live in, and the sum of the sensible heat flux and storage heat flux play a large role. Imperviousness, the leaf area index, the building envelope, surface water, and shade are the dimensions that best explained the Rotterdam urban heat island. We mapped these aspects in two heat-maps that help in setting priorities for implementing climate adaptation measures.

»Hotterdam«: kartiranje družbenih, morfoloških in prostorskih vidikov rotterdamskega mestnega toplotnega otoka

Climate scientists forecast that heat waves will occur more often in the Netherlands in the coming decades. The Hotterdam study accordingly measured urban heat and modelled the surface energy balance in the Dutch city of Rotterdam. It identified in detail the city’s social, morphological, and land-use dimensions using a geographic information system (GIS), 3D models, and satellite images. It used hierarchical and multivariate regression analyses to determine the links between temperatures and the surface energy balance on the one hand, and social, morphological, and land-use aspects on the other. The Hotterdam study did establish a link between the urban heat island effect in Rotterdam and the health of its population. It also statistically explained the high rate of mortality among seniors seventy-five and over during the summer of 2006. The spatial concentration of senior citizens, the average age of the buildings they live in, and the sum of the sensible heat flux and storage heat flux play a large role. Imperviousness, the leaf area index, the building envelope, surface water, and shade are the dimensions that best explained the Rotterdam urban heat island. We mapped these aspects in two heat-maps that help in setting priorities for implementing climate adaptation measures.

热储通量对黄土高原北部柠条林地地表能量平衡的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 热储通量对黄土高原北部柠条林地地表能量平衡的影响 DOI: 10.5846/stxb201707111253 作者: 作者单位: 聊城大学环境与规划学院,中国科学院水利部水土保持研究所 黄土高原土壤侵蚀与旱地农业国家重点实验室;中国科学院地理科学与资源研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41530854，41571130081）；聊城大学博士科研启动基金项目（318051748） Effects of heat storage on surface energy balance in Caragana forest land of northern the Loess Plateau Author: Affiliation: School of Environment and Planning,Liaocheng University,Liaocheng,State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau,Institute of Soil and Conservation,CAS MWR,Yangling;Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:地表能量平衡问题一直是陆面过程研究中的重点和难点问题。以2014年8-10月和2015年4-6月黄土高原北部水蚀风蚀交错带柠条林地涡度相关通量观测数据为依据，分析柠条林地热储通量变化特征，在此基础上分析热储通量对能量闭合度的影响。结果表明，柠条林地各热储通量均表现出明显的季节和日变化规律。在能量平衡方程中，考虑热储通量项后能显著提高柠条林地能量闭合度，平均提高幅度为11.91%。其中，土壤表层热储通量对能量闭合度的贡献最大，占总热储通量的95.63%；光合作用热储通量和大气感热存储通量占总热储通量的比例不足5%，光合热储通量略高于大气感热存储通量；而大气潜热存储通量则降低了能量闭合度，平均降低幅度为0.06%。因此，在分析黄土高原柠条林地能量平衡中热储通量项是不可忽略的。影响柠条林地各热储通量的因素主要有太阳辐射、大气温度、土壤温度和水分。植被生长状况是影响柠条林地热储通量各分量项季节和日变化的重要因素，并对能量闭合度产生影响。 Abstract:Surface-energy balance has become a major and difficult problem in the study of surface land processes. The arbitrary neglect of terms for heat-storage flux is one of the main causes preventing closure of the energy balance during measurements or calculations. We analyzed the characteristics of the mean seasonal and daily variations of heat storage, and the influence of heat-storage flux on energy-balance closure, using eddy-covariance data for a Caragana stand in the wind-water erosion crisscross region of the northern the Loess Plateau collected from August to October 2014 and April to June 2015. All terms for heat-storage flux of the Caragana stand varied considerably both seasonally and diurnally. The energy-balance closure increased at an average of 11.91% when the terms for heat-storage fluxes were included. The soil heat flux was the largest contributor to the energy closure, accounting for 95.63% of the total heat-storage fluxes. The sum of the photosynthetic and atmospheric heat-storage fluxes accounted for less than 5% of the total fluxes, and photosynthesis contributed more than the atmosphere to perceptible heat storage. The latent heat-storage flux, however, decreased the energy-balance closure by 0.06%, indicating that the heat-storage flux should not be neglected when analyzing energy balances for the Caragana stands of the northern the Loess Plateau. The heat-storage fluxes in the Caragana stand were influenced by solar radiation, air temperature, and soil temperature and soil moisture. The growing condition of the vegetation was another important factor that influenced the seasonal and diurnal variation of the terms for heat-storage flux, and which also affected energy closure. 参考文献 相似文献 引证文献

A Study on Retrieval of Storage Heat Flux in Urban Area

A Study on Retrieval of Storage Heat Flux in Urban Area

Urban and regional heat island adaptation measures in the Netherlands

The urban planner's role should be adapted to the current globalised and over-specialised economic and environmental context, envisioning a balance at the regional scale, apprehending not only new technologies, but also new mapping principles, that allow obtaining multidisciplinary integral overviews since the preliminary stages of the design process. The urban heat Island (UHI) is one of the main phenomena aff ecting the urban climate. In the Netherlands, during the heat wave of 2006, more than 1,000 extra deaths were registered. UHI-related parameters are an example of new elements that should be taken into consideration since the early phases of the design process.

Urban and regional heat island adaptation measures in the Netherlands

Urban and regional heat island adaptation measures in the Netherlands

The Analytical Objective Hysteresis Model (AnOHM v1.0): methodology to determine bulk storage heat flux coefficients

Abstract. The net storage heat flux (ΔQS) is important in the urban surface energy balance (SEB) but its determination remains a significant challenge. The hysteresis pattern of the diurnal relation between the ΔQS and net all-wave radiation (Q∗) has been captured in the Objective Hysteresis Model (OHM) parameterization of ΔQS. Although successfully used in urban areas, the limited availability of coefficients for OHM hampers its application. To facilitate use, and enhance physical interpretations of the OHM coefficients, an analytical solution of the one-dimensional advection–diffusion equation of coupled heat and liquid water transport in conjunction with the SEB is conducted, allowing development of AnOHM (Analytical Objective Hysteresis Model). A sensitivity test of AnOHM to surface properties and hydrometeorological forcing is presented using a stochastic approach (subset simulation). The sensitivity test suggests that the albedo, Bowen ratio and bulk transfer coefficient, solar radiation and wind speed are most critical. AnOHM, driven by local meteorological conditions at five sites with different land use, is shown to simulate the ΔQS flux well (RMSE values of ∼ 30 W m−2). The intra-annual dynamics of OHM coefficients are explored. AnOHM offers significant potential to enhance modelling of the surface energy balance over a wider range of conditions and land covers.

Evaluation of an urban land surface scheme over a tropical suburban neighborhood

The present study evaluates the performance of the SURFEX (TEB/ISBA) urban land surface parametrization scheme in offline mode over a suburban area of Singapore. Model performance (diurnal and seasonal characteristics) is investigated using measurements of energy balance fluxes, surface temperatures of individual urban facets, and canyon air temperature collected during an 11-month period. Model performance is best for predicting net radiation and sensible heat fluxes (both are slightly overpredicted during daytime), but weaker for latent heat (underpredicted during daytime) and storage heat fluxes (significantly underpredicted daytime peaks and nighttime storage). Daytime surface temperatures are generally overpredicted, particularly those containing horizontal surfaces such as roofs and roads. This result, together with those for the storage heat flux, point to the need for a better characterization of the thermal and radiative characteristics of individual urban surface facets in the model. Significant variation exists in model behavior between dry and wet seasons, the latter generally being better predicted. The simple vegetation parametrization used is inadequate to represent seasonal moisture dynamics, sometimes producing unrealistically dry conditions.

Thermal mitigation of hydroponic green roof based on heat balance

The creation of green rooftops is an important method for mitigating heat build-up in urban rooftop environments because they lower the sensible heat flux over the rooftop and conductive heat flux into the building. We propose a model for assessing thermal mitigation effects through a hydroponic urban greening system based on heat balance. We conducted an experiment with two different rooftops at two study sites, which were monitored for two months in two different years. Each rooftop was divided into two areas: one bare, the other covered by the hydroponic urban greening system. Parameters measured in both areas were air temperature, surface temperature, and conductive heat flux. The data were analyzed using three thermal mitigation indices. However, it was difficult to show a uniform relationship between the latent heat flux and mitigation indices during the period of analysis. This suggests it would be necessary to include factors such as latent heat flux, conductive heat flux, and water heat storage flux to assess the thermal mitigation effect. Our research indicated that the composition of heat balance terms could estimate thermal mitigation effects in the green roof area independent of the year. The results suggest a principle for assessing the mitigation effects of urban greening on the thermal environment.