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

Ben Crawford,E Scott Krayenhoff,Paul Cordy

doi:10.1007/s00704-016-1922-7

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 (QH) 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 energy-balance literature, and results show good agreement between observations and models for Q* and QH. The unmeasured latent heat flux (QE) is modeled with an updated version of TUF3D and two versions of LUMPS (a forward and inverse application). Both LUMPS implementations predict slightly higher QE 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 QH/LUMPS QE)–3.46 (TUF3D). Storage heat flux (ΔQS) is modeled with TUF3D, the empirical objective hysteresis model (OHM), and the inverse LUMPS implementation. Agreement between models is generally good; the OHM-predicted 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 ΔQS 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.

Highlights

The rapid pace of urban development globally has been well documented, and the case for process-based studies of the urban energy balance has been made extensively in the urban climate literature
There have been several calls for increased study of developing tropical and sub-tropical urban areas because these cities have been underrepresented in urban climate research and their urban populations are forecast to grow at over three times the rate of mid- and high-latitude cities (e.g., Roth 2007)
Observations of Q* conform to an expected diurnal pattern based on solar radiation input and clear skies (Fig. 4)

Summary

Introduction

The rapid pace of urban development globally has been well documented, and the case for process-based studies of the urban energy balance has been made extensively in the urban climate literature. There have been several calls for increased study of developing tropical and sub-tropical urban areas because these cities have been underrepresented in urban climate research and their urban populations are forecast to grow at over three times the rate of mid- and high-latitude cities (e.g., Roth 2007) Within these (sub-) tropical developing cities, the population living in informal, unplanned neighborhoods made of lightweight construction materials (thin, un-insulated walls and roofs) and often with minimal formal services (e.g., water, electricity, transportation) is currently growing 10 % per year globally (UN-HABITAT 2008). According to the local climate zone classification scheme (Stewart and Oke 2012), these neighborhoods can be classified as Blightweight low-rise^ (LL) This classification scheme was originally devised with canopy-layer urbanheat island studies in mind, it summarizes important neighborhood characteristics and provides a useful descriptive framework for energy-balance research

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Conclusion