Urban Physical Environments and the Duration of High Air Temperature: Focusing on Solar Radiation Trapping Effects

Round  1

Reviewer 1 Report

The research goal and methodologies are sound and parts of the discussion, takeaway and conclusions are well laid out. However, there are a couple of minor points/questions I would like to get more clarification.

1)      Line 180~186: What are the difference between AWS 1 and AWS2? Why did they have different temperature records?

2)      Line 206 ~ 211: The height of urban canyon in the urban porosity used the acronym of hmax. The volume of the study area is an ‘A’. Ahmax in the equation is not directly mentioned, which is somewhat confusing. Simply saying “the total volume with the hmax is Ahmax” would suffice.

3)      Line 211: Is the word ‘Urban roughness’ in Line 21 equivalent to the word ‘Surface roughness’ in Table 1, 2? If so, please be consistent.

4)      In table 2, in line 268, the coefficient of Pearson correlation coefficient of ‘Solar radiation’ is a negative (-0.258), which means the stronger solar radiation, the lower duration of high air temperature’. This contradicts with the results from the multivariate regression model. is the sign of direction (+ or -) simply a typo or not?

The authors’ point of possible high albedo group’s compounding effects on air temperature needs to be dealt cautiously. Especially, when considering the range of diurnal air temperature may easily be affected by the radiative heat emitted from the low albedo materials during the night time, the statement from Line 376 ‘Considering road pavement characteristics…  … in densely built-up areas with low SVFs’ could be overly stated without additional analysis for nocturnal temperate data.  The drawback of reflective pavement is not fully proven here without isolating the effect by night time radiation energy or emitted heat from low/high albedo built environment materials. I suggest you revise the tone a bit softer.  

Author Response

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Reviewer 2 Report

Interesting paper in general. Methods needs further detail. AWS system needs to be better explained. The effects of high albedo values could have been further expanded with relevant discussions.

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Reviewer 3 Report

The article provides interesting features of urban temperature using data from more than 200 AWS stations in Seoul. There is no serious problem, although it is desired to add explanation of the AWS.

Main comment:
It is desired to give some details of the AWS system, which is of vital importance to this study. For example, it is better to describe (1) the installation status of the apparatus (on the roof or on the ground?), (2) specification of instruments, and (3) the sampling time interval.

Other comments (Revision is not mandatory):
@ It will be better to add a word "Seoul" to the Title.

@ Line 18 "analysis of interaction effects indicates that high albedo materials diminish mitigation of the effects of high SVFs due to radiation trapping effects" --- This may be misunderstood in a way that high albedo materials can aggravate urban heat in high SVF area. Although correct explanation is made in the main text, it may be better to change expression to avoid misunderstanding of readers.

@ Line 149 "With global warming effects" --- With global warming and urban warming?

@ Line 222 "The average values for the urban porosity, surface roughness, and SVF parameters were 0.94, 9.71, and 0.59, respectively" --- Possibly surface roughness has a unit of length (meter).

@ Line 308 "a multivariate regression analysis focused on" --- It will be better to write the number of independent variables (14?).

@ Please explain the definition of "SVF X high albedo group" in Table 4.

Author Response

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Reviewer 4 Report

This article presents an analytical method for determining the incidence of urban form and building materials in the mitigation of the Urban Heat Islands UHI phenomenon. The Sky View Factor SVF is used as a parameter for measuring Urban Porosity, identified by the authors in “the ratio of the open-air volume in the urban canopy”. The albedo of materials is the other factor that is taken into consideration, observing the ability to increase the heat imprisoned in Urban Island due to multiple reflections. The persistence of high temperature in the afternoon hours is recognized as indicative of the presence of a Heat Island. Although, as the authors themselves say, the study panel is limited to the city of Seoul, Korea, and only to the summer season of 2015, the results show clear correlations, that analytically confirm what can be predicted intuitively. Based on these considerations, the study appears interesting and worthy of being published. It should be noted that cities tend to develop in an uncontrolled way, so the recommendation of line 392 (the urban form with excessive building height and density should be avoided) seems basically unachievable. Vice versa, the surface albedo can be changed even after construction (for example by introducing green roofs or facades), therefore the statement of row 396-397 (materials with appropriate albedo values should be utilized, considering the fact that cooling pavements can impede the effective release of reflected radiation into the atmosphere) is very interesting and deserves further study. In conclusion, in my opinion the article can be published without variations

Author Response

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