THE SUBURBAN ENERGY BALANCE IN MIAMI, FLORIDA © The authors 2007 Journal compilation © 2007 Swedish Society for Anthropology and Geography 331 THE SUBURBAN ENERGY BALANCE IN MIAMI, FLORIDA BY T. NEWTON 1 , T.R. OKE 1 , C.S.B. GRIMMOND 2 AND M. ROTH 3 1 Department of Geography, University of British Columbia, Vancouver, Canada 2 Department of Geography, King’s College London, UK 3 Department of Geography, National University of Singapore, Singapore Newton , T., Oke, T.R., Grimmond, C.S.B. and Roth, M., 2007: The suburban energy balance in Miami, Florida. Geogr. Ann., 89 A (4): 331–347. ABSTRACT. Summertime measurements of local scale energy balance of a suburban site in west Mi- ami, Florida, in 1995 are presented. All of the radia- tion and turbulent heat fluxes were measured di- rectly. In addition several derived surface character- istics are calculated including the albedo, radiation temperature, emissivity, aerodynamic and canopy resistances, Bowen’s ratio, Priestley–Taylor and Mc- Naughton–Jarvis coefficients. The results are used to test parameterizations to calculate several heat fluxes. Most radiation fluxes can be calculated with simple schemes in cloudless conditions but the spa- tial and temporal variability of cloud degrades re- sults greatly. This highlights the value of observing incoming solar radiation since it can form an excel- lent surrogate for daytime net all-wave radiation in all sky conditions. The heat flux results for this warm, wet subtropical site demonstrate similarities with those from similarly developed locations in temperate climates. Interestingly this finding in- cludes the fraction of energy used in evaporation. It is thought that this may be related to the relatively large heat storage in Miami which may reflect the presence of wet soils and free-standing water, the persistently low vapor pressure deficits (7–14 hPa) typical of this humid climate and the relatively poor coupling between the surface and the whole plane- tary boundary layer due to relatively low surface roughness. Key words: urban energy balance, radiation, evaporation, sub- tropical Introduction The surface energy balance is forced by the ex- change of radiation between the Sun, the atmos- phere, and the surface. The surface radiation budget consists of five terms, which can be separated into three categories based on wavelength. The net all- wave radiative flux density (Q*) is equal to the sum of the net shortwave flux density (K* = K↓ – K↑) and the net longwave flux density (L* = L↓ – L↑). Shortwave fluxes refer to radiation in wavelengths ranging from 0.15 to 3.0 μm, and longwave to that between 3 and 100 μm (Oke 1987, p.11). The sur- face radiation budget therefore is: Q* = K↓ – K↑ + L↓ – L↑ (W m –2 ) (1) Surface control is exerted by the surface albedo (α, which is the spectral reflectivity integrated over the shortwave band, i.e. K↑ /K↓ ); the surface emissiv- ity (ε o ) and the apparent surface radiant tempera- ture (T o, which from the Stefan-Boltzmann equa- tion is (L↑ / ε o σ) 0.25 , where σ is Stefan’s constant = 5.67 × 10 –8 W m –2 K –4 . For most natural surfaces the net radiation is partitioned into the conductive exchange between the surface and the underlying substrate (Q G ) and the turbulent fluxes of sensible heat (Q H ) and latent heat (Q E ) between the surface and the overlying atmospheric boundary layer, so that: Q* = Q G + Q H + Q E (W m –2 ) (2) In the case of urbanized systems the equivalent flux of heat across the top of a layer due to heat storage change (∆Q S ) in the volume is more appropriate than that across the interface, (see Oke 1988, p. 472), and the left-hand side of Equation 2 is sup- plemented by an anthropogenic flux contributed by the waste heat released due to human activities in- volving vehicles, space heating/cooling and indus- trial processing (Q F ). In the present study Q F was not evaluated but is likely to be relatively small (say <20 W m –1 ; e.g. Sailor and Lu 2004). The surface energy balance here is evaluated as: Q* = ∆Q S + Q H + Q E (W m –2 ) (3) Very few previous urban energy balance studies