Many studies have found that larger parks might be needed to counteract the Urban Heat Island effects typical in densely populated Asian megacities. However, it is not easy to establish large parks to serve as urban cool islands in Asian megacities, where little space exists for large urban neighborhood parks. Officials in these cities would rather use small areas by replacing heat-absorbing artificial land cover with natural cover. The main objective of this study was to understand the cooling effect of changes in land cover on surface and air temperatures in urban micro-scale environments for supporting sustainable green-space planning and policy in densely built-up areas. This was achieved using measurements at different heights (ground surface, 0.1 m, and 1.5 m) for five land cover types (LCTs) and modeling with the micro-scale climate model ENVI-met. At all vertical measuring points, the average temperature over the entire measurement period had the same hot-to-cold order: asphalt > soil > grass > water > forest. However, the value dramatically decreased as the measuring points became higher. The intensity of hot and cool spots showed the highest value at surface by 18.2˝C, and declined with the height, showing 4.1˝C at 0.1 m and 3.1˝C at 1.5 m. The modeling results indicated that the well-known diurnal variation in surface insolation also occurred in our small domain, among the various LCTs. Based on these findings, providing small-scale green infrastructure in densely built-up areas could be an effective way to improve urban micro-scale thermal conditions.

ABSTRACT:The thermal environment in urban areas is substantially influenced by local surface properties and their modification through human activities. The effects of urban climate on human health are one of the motivations for the development of various urban climate analysis tools. Climate Analysis Seoul (CAS) is a tool that incorporates a meso-scale atmospheric model and conceptual geographic information system (GIS)-based models to provide gridded air temperature deviations based on high-resolution land cover information. The CAS output was evaluated using air temperatures observed at 18 automatic weather stations (AWS) located in the detail region (DR) Eunpyeong. Correlation analyses were performed to reveal the influence of different land cover characteristics and CAS output variables on measured air temperature deviations. Based on the results of the correlation analyses in the study region (SR) Seoul, a regression model (total air temperature distribution, TD ′ ) was developed. It predicts spatially distributed air temperatures based on morphological parameters and an observed reference temperature. Using the TD ′ model, maps of daily maximum air temperatures were produced for the entire area of Seoul with a horizontal resolution of 25 m, and of 5 m for the DR, the latter allows to assess the impacts of different building and vegetation structures on air temperature by resolving buildings. The TD ′ model was evaluated using measurements at eight AWS. The TD ′ model slightly overestimated daily maximum air temperatures in 2007 and 2011, but performed better for 2011, mainly because land cover data represent the final state of the urban development. The TD ′ model appears to be a suitable tool for estimating air temperature distributions at building-resolving resolutions. It can be used to assess changes in the thermal environment and heat-related hazards through urban development plans already ahead of their realization.KEY WORDS urban climate analysis; urban planning; urban heat island; urban multi-scale temperature distribution

Quantitatively describing effects caused by trees is a challenging issue for sky view factor (SVF) studies. The complex geometrical shapes of trees and the seasonally changing canopy volume caused by leaf growth and defoliation have forced SVF users to disregard trees in their analyses or to apply a simple geometric object, such as a rectangular pole or vertically elongated ellipsoid. The three-dimensional point cloud (3DPC) method is useful for quantitative analysis of urban settings by describing the structured spatial complex in detail, not only by shape itself but also with many meaningful indices such as SVF. We here proposed a new SVF analysis method based on 3DPC. Stereoscopic projection was applied to project 3DPC on the virtual hemisphere. From intensive analysis of 3DPC SVF in a normal urban complex area, we discerned the effects caused by trees. The results showed that the tree effect derived from 3DPC SVF in an urban complex is clearly described by a comparison between two cases (trees and no trees). Trees with topography play an important role and contribute to the heat balance in an urban complex.KEY WORDS sky view factor (SVF); three-dimensional point cloud (3DPC); virtual hemisphere; stereoscopic projection; tree effect; urban complex; hemispherical 3DPC SVF; continuous 3DPC SVF

Air temperature deviation (ATD) is one of major indicators to represent spatial distribution of urban heat island (UHI), which is induced from the urbanization. The purpose of this study is to evaluate the accuracy of air temperature deviation about Climate Analysis Seoul (CAS) workbench, which had developed by National Institute Meteorological Science and TU Berlin. Comparison and correlation analysis for CAS ATD including meso-scale air temperature deviation, local-scale air temperature deviation, total air temperature deviation, surface heat flux deviation, cold air production deviation among meso-scale numerical modelling variable in 'Seoul Region', micro-scale numerical modelling in 'Detail Region', and CAS workbench variable using observation data in ground stations. Comparison between night time OBS ATD and CAS ATD show that have most close values. Most of observations (dT max and dT min ) have highly positive (dT SHP , dT CA , MD, TD, f BS , f US , f WS , h B ) and negative (f VS , f TV , h V , Z) correlations. However, CAS workbench needs further improvement of both observational framework and analytical framework to resolve the problems; (1) night time OBS ATD of has closer values in compare with at high rise mountain area and (2) correlations are very dependable to meteorological scale.

The purpose of this study is for the fundamental understandings about building morphological parameters and aerodynamic roughness parameters of Seoul, Korea using the detailed urban geographic information datasets. Applied roughness parameter calculations are based on a digital map of buildings with lot area polygons. The quality of the developed roughness length (z 0 ) of Seoul was evaluated with densely installed 107 automatic weather stations. The correlation coefficient results between averaged wind speeds of AWS data and averaged z 0 is −0.303 in night and −0.398 in day (200 m radii circles case). Further z 0 enhancement should follow by considering other surface features such as high tree and orography of Seoul. However, this study would meet the needs to for local-or meso-scale meteorological modeling applications of Seoul. However, further studies would require for enhancing the z 0 applications of Seoul.