Comparison of four methods to estimate urban heat storage.

The relative performance of four independent methods to estimate the magnitude and diurnal behavior of net heat storage fluxes (ΔQS) in a city center is assessed. This heat flux is a significant but understudied component of the urban surface energy balance (SEB). Direct measurement of this SEB term at the local scale (horizontal length scale 102–104 m) is practically unattainable primarily because of the complex array of materials and the three-dimensionality of urban systems. Results of an 8-day summertime observational study at a site in the center of Marseille, France, are presented. This locale is an ideal environment for such research because of the warm, dry climate (hence the SEB is dominated by sensible heat exchanges) and the high density of tall buildings with thick walls (hence it has a large thermal mass that favors heat storage as a component of the SEB). Estimates of ΔQS derived as residuals in the SEB, after the remaining terms are measured directly, (termed RES) are compared with those calculated from a parameterization scheme [objective hysteresis model (OHM)], a local-scale numerical model [Town Energy Balance model (TEB)], and a bulk heat transfer method [thermal mass scheme (TMS)]. Inputs to the methods include observed meteorological data and morphometric properties of the urban site. All approaches yield a similar diurnal course. The OHM and TEB methods tend to slightly overestimate storage uptake by day when compared with the RES, whereas TMS slightly underestimates it. All methods underestimate heat storage release at night when compared with RES and show some sensitivity to wind speed, especially above about 5 m s−1. OHM estimates perform satisfactorily in the mean but miss short-term variability and are poor at night. TEB simulations show the best agreement with RES results, particularly at night. TMS values are comparable to those from the other methods, but its extensive input requirements render it almost impractical. Overall, the convergence of results is reassuring but the lack of a standard for quantifying heat storage and the spread of results mean this term remains a source of imprecision in urban energy balance measurement and modeling. Copyright 2006 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyright@ametsoc.org.Arts, Faculty ofGeography, Department ofReviewedFacult