Enhancing the city-level thermal environment through the strategic utilization of urban green spaces employing geospatial techniques.

Smart urban planning needs to have a multicriteria-based approach to prevent the deteriorating local thermal climate. Maximizing the cooling potential using the available grey infrastructure would be the utmost priority of future smart cities. Remote sensing and GIS can be the appropriate tools to develop a climate-resilient urban planning framework. Studies are needed to include different features of vertical and horizontal landscaping to mitigate heat stress and enhance liveability at the city level. With this goal, the current work outlined a holistic approach to efficiently using green spaces with minimal reconstruction. The problem of regional climate threat was evaluated with urban heat island characterization. Moran's I clustering identified nearly 12% of the study area to be under considerable heat stress during summer days. Multiple techniques, such as mapping local climate zones, segment mean shift-based roof extraction, vegetation index computation, solar azimuth-based green wall site selection, etc., were applied to formulate solutions and provide an integrated method for city-level environment enhancement. A considerable area was identified as most suitable for green roof cover, and it was also computed that the transition towards green roof at only these locations may bring down the maximum heat island intensity by 0.74 °C. Additionally, solar zenith, illumination effect, and building height information were combined to create a distinct method where vertical plantation would flourish exceptionally. A rigorous assessment of more than 130 urban green spaces further quantified the relation between landscape geometry and cooling effect to provide optimum green space designs for future urban planning.

Spatial patterns of greenspace cool islands and their relationship to cooling effectiveness in the tropical city of Chiang Mai, Thailand.

Urban greenspaces provide evaporative cooling, which can help effectively mitigate the urban heat island (UHI) to achieve a sustainable urban climate. This study examines the cooling effects of greenspace patterns on urban cool islands (UCIs) at the patch level in an urban environment. The effects of 1155 patches of greenspace cool islands (GCIs) on UCIs of the Chiang Mai metropolitan area in Thailand were identified from a satellite image, and the relationships between them were analyzed through correlation and regression analyses. The results indicate that (1) spatial patterns of GCIs have significant effects on their cooling potential, while urban areas with more green patch coverage encounter stronger cooling effects; also, (2) our correlation analysis of three fundamental and widely recognized classes of landscape metrics (area, shape, and core of GCIs with temperature change) shows that the most important metric of effective cooling is the core area. These findings can help planners understand greenspaces established in urban areas and plan urban greenspace to mitigate UHI effects.

Development of a bioclimatic wind rose tool for assessment of comfort wind resources in Sydney, Australia for 2013 and 2030.

This study assessed the effect of wind on human thermal comfort by preforming outdoor urban climatic comfort simulations using state-of-the-art heat-balance models of human thermo-physiology (Universal Thermal Climate Index-UTCI). A series of simulations for computing "wind cooling potential" have been performed using the UTCI index temperatures. The comfort cooling effect of wind has been estimated by modelling with wind taken into account, and under calm wind (0.05 m/s) (ΔUTCI). A novel wind rose biometeorological data visualisation tool that integrates an additional thermal comfort dimension into the conventional climatology wind rose visualisation was developed in this study. The new wind rose graphic tool identifies "predominant" wind directions, and whether or not they are "desirable" from the human thermal comfort point of view. This tool's utility lies in its identification of the optimal building orientation in its surrounding urban morphology, based on the cooling potential of wind resources when enhanced ventilation is desirable for thermal comfort.

Soil texture mediates the surface cooling effect of urban and peri-urban green spaces during a drought period in the city area of Hamburg (Germany).

Urban green spaces (UGS) and peri-urban green spaces (P-UGS) play a crucial role in reducing the land surface temperature within the urban environment, especially during heat waves. Although their cooling effect generally is due to shading and evaporation, the role of soil texture and soil water availability on surface cooling remains largely unexplored. This study investigated the impact of soil texture on the spatio-temporal patterns of LST in different UGSs and P-UGSs in Hamburg (Germany) during a hot summer drought period. The LST and the Normalized Differentiated Moisture and Vegetation Indices (NDMI, NDVI) were calculated based on two Landsat 8 OLI/TIRS images from July 2013. Non-spatial and spatial statistical approaches such as stepwise backward regression or Hotspot (Getis-Ord Gi*) analyses were applied explaining LST distributions in relation to soil texture within each UGS and P-UGS. All GSs were clearly characterized as surface cooling islands whereas, for each GS, an individual thermal footprint was observed. Within all GSs, the LST patterns showed a significant negative relationship to NDMI values, whereas the NDVI values and the elevation were of minor importance. Soil texture was found to influence the LST distribution significantly in most UGSs and P-UGSs, where sites on clay-rich soils showed the highest LST values compared to sites on sand- or silt-rich soils. For example, in parks, clayey soils showed a mean LST of 25.3 °C whereas sand-dominated sites had a mean LST of only 23.1 °C. This effect was consistent throughout all statistical approaches, for both dates and across most GSs. This unexpected result was explained by the very low unsaturated hydraulic conductivity in clayey soils which limits plant water uptake and transpiration rates responsible for the evaporative cooling effect. We concluded that soil texture has to be considered for understanding and managing the surface cooling capacity of UGSs and P-UGSs.

Outdoor thermal performance of heterogeneous urban environment: An indicator-based approach for climate-sensitive planning.

The thermal profile of the urban built-up area is essential for reducing the impact of built-up areas on urban heat stress. This study quantifies the variations in the outdoor thermal profile of built forms in a heterogeneous urban area. A two-step process was adopted to quantify built form induced heat stress. The build form typologies referred to as Urban Built Form (UBFX) were clustered based on parameterised build form indices (sky view factor, built height etc.) using statistical data reduction. The heat stress of the categorised UBFs was then examined through field measurements and radiation simulation model. Variations in thermal variables were assessed using three indices - Cooling Potential (CP), Humidex (Hx) and Mean Radiant Temperature (Tmrt) that collectively define the thermal profile of each UBF. A novel Heat Stress Risk Index (HSRI) was conceptualised and computed to represent the aggregate risk of a particular UBF towards heat stress. It was found that among the UBFs, the medium-rise compact (UBF 4) show lowest rate of cooling, exposure to high Tmrt, and high discomfort levels throughout the day and therefore exhibit thermally stressed profile. High rise-open typologies (UBF1) have high Tmrt and Hx during the noon (12:00 to 14:00 h), but their high cooling potential reduces the thermal impact of its built form during the cooling hours (18:00 to 20:00 h). Three thermal indices provide varied aspects of thermal performance of UBFs and HSRI cumulatively represents the heat stress risk of the UBFs. This study is a proof of concept, that uses empirical evidence to demonstrate thermal variations in urban built forms during calm and clear weather conditions. Results indicate the significance of built form indices as a policy variable for framing climate sensitive urban development regulations that aim to achieve a thermally efficient built environment.