The urban energy balance of a lightweight low-rise neighborhood in Andacollo, Chile

Abstract

Worldwide, the majority of rapidly growing neighborhoods are found in the Global South. They often exhibit different building construction and development patterns than the Global North, and urban climate research in many such neighborhoods has to date been sparse. This study presents local-scale observations of net radiation (Q * ) and sensible heat flux (Q H ) from a lightweight low-rise neighborhood in the desert climate of Andacollo, Chile, and compares observations with results from a process-based urban energy-balance model (TUF3D) and a local-scale empirical model (LUMPS) for a 14-day period in autumn 2009. This is a unique neighborhood-climate combination in the urban energybalance literature, and results show good agreement between observations and models for Q * and Q H . The unmeasured latent heat flux (Q E ) is modeled with an updated version of TUF3D and two versions of LUMPS (a forward and inverse application). Both LUMPS implementations predict slightly higher Q E than TUF3D, which may indicate a bias in LUMPS parameters towards mid-latitude, non-desert climates. Overall, the energy balance is dominated by sensible and storage heat fluxes with mean daytime Bowen ratios of 2.57 (observed Q H / LUMPS Q E )-3.46 (TUF3D). Storage heat flux (ΔQ S ) is modeled with TUF3D, the empirical objective hysteresis model (OHM), and the inverse LUMPS implementation. Agreement between models is generally good; the OHMpredicted diurnal cycle deviates somewhat relative to the other two models, likely because OHM coefficients are not specified for the roof and wall construction materials found in this neighborhood. New facet-scale and local-scale OHM coefficients are developed based on modeled ΔQ S and observed Q * . Coefficients in the empirical models OHM and LUMPS are derived from observations in primarily non-desert climates in European/North American neighborhoods and must be updated as measurements in lightweight low-rise (and other) neighborhoods in various climates become available.

Integrating Urban Form, Function, and Energy Fluxes in a Heat Exposure Indicator in View of Intra-Urban Heat Island Assessment and Climate Change Adaptation

“…In the literature, several studies have modeled the urban energy fluxes using a remotely-sensed approach [66][67][68][132][133][134][135][136][137][138]; however, only few of them made synchronous measurements of the turbulent fluxes available for validation purposes. Here, the obtained accuracy is considered to be consistent with the reported errors in recent studies of long-term, remotely-sensed turbulent fluxes [68,81,86]. Furthermore, the present work extends the current knowledge of the applicability of the downscaled satellite T s in the urban Q H estimation, which to the authors' knowledge has only be examined in [68].…”

“…Heat storage uptake and release in urban systems is typically estimated using one of the following techniques: the Objective Hysteresis Model (OHM) [45,84], the modeling of heat transfer through urban surfaces [68,85], or the closure of the surface energy balance [86,87]. The OHM methodology is a robust approach that provides accurate estimates compared to observational data, especially when the representation of the typical average storage magnitude, rather than its short-term fluctuations, is of primary concern [88].…”

Parameterization of Urban Sensible Heat Flux from Remotely Sensed Surface Temperature: Effects of Surface Structure

“…TUF-3D has also been used to simulate the sensible heat fluxes in a lightweight low-rise neighborhood in Andacollo, Chile, and the results were compared to observations and a local-scale empirical model (LUMPS) for a 14-day period in the autumn of 2009. The results showed good agreement between observed and modeled sensible heat fluxes [43]. TUF-3D was originally tested against urban climate, surface temperature, and energy balance data from Vancouver, Canada, and Basel, Switzerland, and it has been applied in diverse cities.…”

“…One factor was that r r was underestimated when r r was larger than 40 s/m ( Figure 6). Additionally, although the sensible heat flux simulated by TUF-3D has been validated by several measurements [40,43], TUF-3D has several limitations when applied to studies of sensible heat flux. For example, it only deals with uniform building footprints and represents the momentum forcing and associated impacts of turbulence on sensible heat transfer in a simplified fashion.…”

“…Note that the ratio of a building's height to the street width changes with both λ p and H/L. TUF-3D performs better during daytime, and thus results from the daytime (8:00 to 17:00) will be analyzed [43]. We varied the λ p value from 0.05 to 0.6 with 0.05 steps and the ratio of building height to width (H/L) from 0.5 to 6 with 0.5 steps in our numerical experiments with TUF-3D, which thus explored most urban densities and aspect ratios [45].…”