Urban energy exchanges monitoring from space

Abstract

One important challenge facing the urbanization and global environmental change community is to understand the relation between urban form, energy use and carbon emissions. Missing from the current literature are scientific assessments that evaluate the impacts of different urban spatial units on energy fluxes; yet, this type of analysis is needed by urban planners, who recognize that local scale zoning affects energy consumption and local climate. Satellite-based estimation of urban energy fluxes at neighbourhood scale is still a challenge. Here we show the potential of the current satellite missions to retrieve urban energy budget fluxes, supported by meteorological observations and evaluated by direct flux measurements. We found an agreement within 5% between satellite and in-situ derived net all-wave radiation; and identified that wall facet fraction and urban materials type are the most important parameters for estimating heat storage of the urban canopy. The satellite approaches were found to underestimate measured turbulent heat fluxes, with sensible heat flux being most sensitive to surface temperature variation (−64.1, +69.3 W m−2 for ±2 K perturbation). They also underestimate anthropogenic heat fluxes. However, reasonable spatial patterns are obtained for the latter allowing hot-spots to be identified, therefore supporting both urban planning and urban climate modelling.

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

“…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 Ts in the urban QH estimation, which to the authors' knowledge has only be examined in [68]. Downscaled thermal data are necessary in the estimation of high-resolution daily…”

“…Remote sensing methods have often been used in natural [63][64][65] and urban environments [66][67][68] for the estimation of the turbulent surface fluxes using the aerodynamic resistances for heat (rH) [s m −1 ] and moisture (rV) [s m −1 ] transfer:…”

“…Remote sensing methods have often been used in natural [63][64][65] and urban environments [66][67][68] for the estimation of the turbulent surface fluxes using the aerodynamic resistances for heat (r H ) [s m −1 ] and moisture (r V ) [s m −1 ] transfer: methodology that combines ridge regression with multiple predictor variables and a high-resolution emissivity map [55]. MODIS calibrated radiances product (MOD/MYD021KM) and precipitable water product (MOD/MYD05-L2) were accessed from the National Aeronautics and Space Administration's (NASA's) Level-1 and Atmosphere Archive and Distribution System (LAADS) Distributed Active Archive Center (DAAC).…”

“…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].…”

“…Three techniques are commonly employed to estimate Q F [46]: (a) the energy budget residual approach [68,85,96], (b) top-down estimates based on the disaggregation of coarse energy consumption statistics [97][98][99], and (c) bottom-up estimates that model energy consumption at fine scales [100][101][102]. A synergy of the latter two methodologies [103,104] can provide the necessary balance between the data availability and required accuracy [105].…”