Urban features at neighborhood scale to assess and mitigate the heat island in arid Mendoza, Argentina

MICHELE ZINZI; M. BELÉN SOSA; ERICA N. CORREA

Hyderabad

Conferencia; 5th International Conference on Countermeasures to Urban Heat Islands (IC2UHI); 2019

International Institute of Information Technology

Some urban features like streets orientations and widths, blocks sizes, buildings foot prints, among others, define the layout and grid of cities. These resulting urban forms interact with the city climate. Particularly in arid zones, these interactions represent a major challenge in order to reduce the urban heat island (UHI) phenomenon. By generates appropriate designs at neighborhood scale which help to decrease the outdoor air temperatures, UHI reduction would be possible to achieve.This study assesses the thermal behavior of three low-density neighborhoods and analyzed the possibility to apply cool materials as an UHI´s mitigation strategy in the arid Metropolitan Mendoza Area, Argentina (MMA). This city has an urbanistic particular characteristic because a most of the streets are forested, regarding its arid context. As the street trees are already considered an effective UHI mitigation strategy, evaluate the outdoor thermal improved by implementing cool materials is considered an important planning policy. The selected three study cases have different layout grids (multi-azimuthal, rectangular and Cul-de-Sac) but similar features (houses typology, materials, street trees and LCZ class) that allows to contrast their thermal behavior. Also, these neighborhoods are located in different areas of the MMA around 6.5 and 4.8 km to the downtown. In order to analyze the impact of the UHI reduction by apply cool materials, four boundaries points that are coincident with the MMA urbanization limits (North, South, East and West sectors) and a point in the downtown were monitored.Their microclimates were monitored every 15 minutes with HOBO® data-loggers installed at 2 m height in a representative urban canyon inside each neighborhood, in the downtown and in the four boundaries points during the same summer period (from January 8th to February 6th 2014). With the neighborhoods microclimatic data a set of scenarios were try to test the effectiveness to apply cool materials (surfaces albedo´s roofs= 0.7, walls= 0.3 and floors= 0.5). ENVI-met software was used to simulate these scenarios. A calibration procedure was made for each neighborhood layout, by comparing the series of air temperature measurements from January 18th with the corresponding simulated values. Also, the SVF values of each urban canyon where the data-logger was installed were adjusts with those generated by the ENVI-met model. Then the three scenarios were statistically evaluated using a set of indices that describe the magnitude of the difference between the observation and prediction: R2, RMSE, RSMEs, RSMEu, MAE and MBE. After made several simulations adjustments the scenarios achieved a good statically accuracy (R2 0.91, 0.95 and 0.99). The results of the first stage of the study ?cool materials application? show that as was expected the maximum and average air temperatures decrease in all the neighborhoods but its intensity depends on the design layout (Δ maximum between 1.1 to 2.4ºC, average between 0.6 to 2.3ºC). Regarding the minimum air temperatures there is not significant reductions achieved. These findings are in concordance with researches that have been demonstrating a temperature change pattern during daytime and little or no decrease during the night.By analyzing each neighborhood behavior with the downtown and the boundaries points, second stage ?UHI reduction? significant air temperatures reductions were achieved. In the case of the downtown versus neighborhoods performance contrast significant minimum and average air temperatures reduction were found (Δ minimum between 1.2 to 3.1ºC, average between 0.8 to 1.5ºC). Also a few reductions could be achieved, by contrast the MMA´s boundaries points (Δ minimum between 0.1 to 0.8ºC, average between 0.2 to 0.9ºC).These findings highlight that suitable neighborhood layouts, that incorporates cool materials, could help to decrease the UHI phenomenon and avoid its extension to the boundaries of arid cities. This strategy is feasible to apply in the planning regulations and policies at neighborhood scale by promoting mitigation measures into new developments as well as during retrofitting and maintenance.