Efficient urban canopy parametrization for atmospheric modelling: description and application with the COSMO-CLM model (version 5.0_clm6) for a Belgian Summer

Abstract

Abstract. This paper presents the Semi-empirical URban-canopY parametrization SURY, which bridges the gap between bulk urban land-surface schemes and explicit-canyon schemes. Based on detailed observational studies, modelling experiments and available parameter inventories, it offers a robust translation of urban canopy parameters containing the three-dimensional information into bulk parameters. It is extremely suitable for an intrinsic representation of canopy-dependent urban physics in existing bulk urban land-surface schemes of atmospheric models. At the same time, it delivers high efficiency in terms of computational cost for long-term climate modelling and numerical weather prediction. SURY enables versatility and consistency in choosing between the urban canopy parameters from bottom-up inventories and bulk parameters from top-down estimates. SURY is tested for Belgium at 2.8 km resolution with the COSMO-CLM model (version 5.0_clm6) that is extended with the bulk urban land-surface scheme TERRA_URB (version 2). The model reproduces very well the urban heat islands observed from in-situ urban-climate observations, satellite imagery and tower observations, which is in contrast to the original COSMO-CLM model without an urban land-surface scheme. As an application of SURY, the sensitivity of the COSMO-CLM model in terms of land-surface temperatures, air temperatures and associated urban heat islands is quantified for the urban canopy parameter ranges from the Local Climate Zones classification system. On the one hand, their city-scale effect shows that additional urban canopy information has potential for improving regional atmospheric modelling. On the other hand, the model performance and its sensitivity to the different urban canopy parameters largely depend on the temperature quantity considered. Such an ambiguity demonstrates that a multi-variable model evaluation is a requirement for improving and comparing online urban atmospheric modelling strategies.

Impact of urban canopy models and external parameters on the modelled urban energy balance in a tropical city

“…Their results conclude that changes in land‐surface properties (hydrothermal or geometric) have a significant impact on the evolution of the overlying boundary layer. In addition, Wouters et al (2016) tested urban canopy parameter value ranges from the Local Climate Zones (Stewart and Oke, 2012) in an online simulation over the Belgian territory with COSMO‐CLM coupled to TERRA_URB. Their study, amongst other results, reveals that, with respect to surface temperatures, air temperatures and associated urban heat islands, one should prioritize those parameters that are most sensitive: the thermal parameters and the anthropogenic heat emissions.…”

“…TERRA_URB (Wouters et al , 2015, 2016) is the bulk urban land‐surface scheme of the COSMO(‐CLM) model. It represents the variability of ground heat and moisture transport, the turbulent transfer of momentum, heat and moisture, and the surface–atmosphere radiative exchanges in urban areas.…”

“…This effort helped to identify the dominant physical processes, the level of complexity needed in an application specific context, and parameter requirements. Other ULSM evaluations in online mode (coupled to an atmospheric/climate model) include: a single‐ and a multi‐layer urban parametrization within the Coupled Ocean–Atmosphere Mesoscale Prediction System for the New York City metropolitan area (Holt and Pullen, 2007); various urban canopy schemes (slab, single‐layer and multi‐layer with and without a building energy model) in the Weather Research and Forecasting/Chemistry model to evaluate the regional climate and air quality of the Yangtze River Delta (China) (Liao et al , 2014), and high‐resolution regional climate simulations over Berlin (Germany) with the COSMO‐CLM regional climate model coupled to the Town Energy Budget (TEB) model (Trusilova et al , 2013, 2015), the Double Canyon Effect Parametrization (DCEP) scheme (Schubert and Grossman‐Clarke, 2012) and TERRA_URB (Wouters et al , 2015, 2016).…”

“…A recent study by Karsisto et al (2016a, 2016b) answered this call and tested the performance of three ULSMs for several sites in and around the high‐latitude city of Helsinki (Finland): the Community Land Model (CLM; Lawrence et al , 2011), the Surface Urban Energy and Water Balance Scheme (SUEWS; Järvi et al , 2011, 2014) and SURFEX (Masson et al , 2013). The present study extends this effort by evaluating the three above‐mentioned ULSMs together with TERRA_URB (Wouters et al , 2015, 2016) over a residential neighbourhood in a tropical city. Even though currently most of the rapidly expanding urban areas are located in (sub)tropical regions (Seto et al , 2012), the total number of (sub)tropical urban climate studies is limited Roth (2007).…”

Urban–rural differences in near‐surface air temperature as resolved by the Central Europe Refined analysis (CER): sensitivity to planetary boundary layer schemes and urban canopy models

“…The main benefit of applying default parameter values is an easy transfer of the CER to other cities. Wouters et al () also detected that the sensitivity of T 2 and surface temperature to parameter values is lower than the sensitivity to different UCMs when using the COSMO‐CLM model. While some former studies (Kim et al , ; Fallmann et al , ; Shaffer et al , ) also revealed no improvements with increasing complexity, other studies (Kusaka et al , ; Kim et al , ; Li and Bou‐Zeid, ) detected that more complex schemes (SLUCMs or multi‐layer UCMs) perform better than slab models.…”