The urban energy balance of a lightweight low-rise neighborhood in Andacollo, Chile
The urban energy balance of a lightweight low-rise neighborhood in Andacollo, Chile
Ben Crawford 0 1 2 3 4
E. Scott Krayenhoff 0 1 2 3 4
Paul Cordy 0 1 2 3 4
0 Present address: Department of Meteorology, University of Reading , Reading , UK
1 Department of Geography, University of British Columbia , Vancouver , Canada
2 Present address: Cordy Geoscience , Squamish, BC , Canada
3 Department of Mining Engineering, University of British Columbia , Vancouver , Canada
4 Present address: School of Geographical Sciences and Urban Planning, Arizona State University , Tempe, AZ , USA
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 energybalance 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 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 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.
1 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 also 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). At
present, over one billion people worldwide are estimated to
live in these neighborhoods (UN-HABITAT 2008) and it is
important to incorporate these areas into environmental
models across a range of scales (micro-global) for a variety
of applications (e.g., urban planning, resource consumption,
thermal comfort, air quality, hydrology).
According to the local climate zone classification scheme
(Stewart and Oke 2012), these neighborhoods can be
classified as Blightweight low-rise^ (LL). Although 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.
The urban energy balance can be expressed for a
neighborhood-scale volume (including the 3-day urban
surface and air volume extending from the surface through the
roughness sub-layer) as (Oke 1988):
where the net radiation (Q*) and anthropogenic heat flux (QF)
are energy inputs to the system, which are partitioned between
sensible heat flux (QH), latent heat flux (QE), and storage heat
flux (ΔQS). ΔQA is energy flux from advection and is
typically assumed to be zero based on assumptions of a
continuous, extensive, and homogeneous study surface, although in
areas with larger (mesoscale) circulations, this assumption is
unlikely to hold (e.g., Pigeon et al. 2007).
The terms of the energy balance of lightweight low-rise
neighborhoods are expected to contrast with other local
climate zones due to differences in constr (...truncated)