Comparison of Urban Heat Island Intensity Estimation Methods Using Urbanized WRF in Berlin, Germany

Julian Vogel,Afshin Afshari

doi:10.3390/atmos11121338

Julian Vogel, Afshin Afshari

Open Access

https://doi.org/10.3390/atmos11121338

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Journal: Atmosphere	Publication Date: Dec 9, 2020
Citations: 21	License type: CC BY 4.0

Affiliation: Fraunhofer Institute for Building Physics

Abstract

In this study, we present a meso-scale simulation of the urban microclimate in Berlin, Germany, using the Weather Research and Forecasting (WRF) numerical weather prediction platform. The objective of the study is to derive an accurate estimate of the near-surface urban heat island (UHI) intensity. The simulation is conducted over a two-week summer period. We compare different physical schemes, different urban canopy schemes and different methods for estimating the UHI intensity. The urban fraction of each urban category is derived using the Copernicus Impervious Density data and the Corine Land Cover data. High-resolution City Geography Markup Language (CityGML) data is used to estimate the building height densities required by the multi-layer urban canopy model (UCM). Within the single-layer UCM, we implement an anthropogenic heat profile based on the large scale urban consumption of energy (LUCY) model. The optimal model configuration combines the WRF Single Moment Five-Class (WSM5) microphysics scheme, the Bougeault–Lacarrère planetary boundary layer scheme, the eta similarity (Mellor–Yamada–Janjic) surface layer scheme, the Noah Multi-Parameterization land surface model, the Dudhia and Rapid Radiative Transfer Model (RRTM) radiation schemes, and the multi-layer UCM (including the building energy model). Our simulated UHI intensity results agree well with measurements with a root mean squared error of 0.86K and a mean bias error of 0.20K. After model validation, we proceed to compare several UHI intensity calculation methods, including the ‘ring rural reference’ (RRR) method and the ‘virtual rural reference’ (VRR) method. The VRR mthod is also known as the ‘urban increment’ method. We suggest and argument that the VRR approach is superior.

Highlights

Until the late 1990s, the study of the urban microclimate was, to a large extent, dependent on field experiments [1]
We focused on two different investigations: (i) the first step was an assessment of the sensitivity of model accuracy to variations of physical and urban parameterizations, which led us to select the combination that produces the most accurate estimation of the urban heat island (UHI) intensity; (ii) the second step was a comparison of different UHI intensity evaluation methods
We presented a meso-scale simulation of the urban microclimate in Berlin during the summer period 21 June 2010 to 4 July 2010

Summary

Introduction

Until the late 1990s, the study of the urban microclimate was, to a large extent, dependent on field experiments [1]. The “bulk” or “slab” approach [4] would be adopted whereby the urban soil properties (heat capacity, thermal conductivity, surface albedo, aerodynamic roughness length, etc.) used in the surface heat balance equation were modified in order to distinguish the urban area from the surrounding rural area [5]. While this approach, where buildings are modeled via increased roughness in urban areas, is associated with a low number of parameters and is coupled with the atmospheric model [6], it does not properly represent the geometric characteristics of urban areas [7]. It does not provide an accurate estimate of the conditions within urban canyons.

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