Comment on Bettignies et al. The Scale-Dependent Behaviour of Cities: A Cross-Cities Multiscale Driver Analysis of Urban Energy Use. Sustainability 2019, 11, 3246

Round 1

Reviewer 1 Report

The authors of the Comment show a deep understanding of the research subject. Although I do not agree with all of their views, my opinion is that the remarks offered in the Comment may improve the future work of Bettignies et al. Specifically, I do not agree with the assessment that the authors appear to have a number of misconceptions on the nature of the urban scaling frameworks, and that the application of urban scaling models to energy consumption is basically impossible (sections 2.1, 2.2 and 2.3 of the Comment). However, I agree that the Authors appear to have made mistakes in the Methodology of the original article (section 3 of the Comment), which would have affected the robustness of the results and conclusions.

1. I suggest to give a short explanation about why references [2,3] are still considered to be relevant today? The theories and concepts postulated in [2, 3] are still valid for present-day research of urban scaling?
2. In the Comment, you say that "The problem in the authors’ work arises from their explicitly combining data from cities and MTUs from very different urban systems that have no reason to share an underlying baseline energy consumption... ". But Bettignies et al. also say that "... even though cities seem to be very complex, different from one another and being located in very different regions of the world, they might share common macroscale (city-scale) simple behaviours." Here, as impartial observer, I wonder if there is an absolutely right and an absolutely wrong approach, or your view is just that urban scaling cannot be applied for modeling urban energy use? 
3. You argue that urban scaling frameworks is ill-suited for examining  intra-urban heterogeneity at micro-levels when the authors hypothesize scale-invariance between large metropolitan areas and smaller intra-urban units. I agree that the scale-invariance hypothesis is a bit of a stretch but at the same time I do not see any clear evidence to counter this hypothesis. Bettencourt et al. [8] state that urban scaling effects vanish below a critical scale, which depends on the type of urban indicator. For instance, this critical scale is 14,454 inhabitants for the rate of violence in Brazilian metropolitan areas but only 257 inhabitants for income in Japanese metropolitan areas. Bettencourt et al. [8] do not explicitly say that urban scaling is unfit for urban energy use and do not report a critical scale in this case. Then, what is the critical scale for the urban energy use? How can we be certain that the scale-invariance hypothesis for urban energy use is wrong and not worth of further investigation?
4. The authors look into the power-law relationship between urban size and urban energy consumption. You argue that this power-law relationship is questionable. However, the authors leave this open to debate, a question for further research by saying that "previously found city-scale power-laws of intensity of energy use do not seem to hold when taking into account smaller cities and looking at indicators of intensity of energy use other than total energy use per capita. This relativizes and gives new perspectives to the previous researches on scaling laws of urban energy use [13,14] for megacities. Indeed, none of the evidence and data collected for this study contradicts previous research: the overall tendencies are that intensity of energy consumption increases with income and decreases with population density and population size. However, no evidence clearly
   supports previous findings either. On the contrary, the relations seem to be more complex when extending the case studies. In order to take other cities into account, better indicators of the intensity of energy use or more complex relations might be necessary. Future research should therefore investigate how those relations could be extended to more cities, using more complex regression methods, larger
   sets of case studies and features."

Author Response

Please see the attachment.

Author Response File: Author Response.pdf