Modeling Urban Heat Islands and Thermal Comfort During a Heat Wave Event in East China With CLM5 Incorporating Local Climate Zones

Abstract

The urban expansion‐induced heat can exacerbate heat stress for urban dwellers, especially during heat waves. With a focus on the intra‐urban variability of urban heat islands (UHIs) and thermal comfort, the urban parameterization within the Community Land Model version 5 (CLM5) was modified incorporating the local climate zones (LCZs) framework, named CLM5‐LCZs, to simulate the urban climate during a heat wave (HW) event in the summer of 2013. The evaluation of model performance demonstrated that it did a reasonable job of simulating surface energy balance and thermal regimes in cities against observational fluxes from a flux tower measurement site and temperatures from automatic meteorological stations in Nanjing, China. Then we investigated the characteristics and causes of UHIs associated with local background climate, intra‐urban inhomogeneity and HW intensity in East China. The results exhibited that daytime and nighttime canopy urban heat island intensity (CUHII) were highest in the Compact Low Rise (LCZ3) and the Compact High Rise (LCZ1) areas respectively, while surface urban heat island intensity (SUHII) peaked in the Large Low Rise (LCZ8) and the Compact High Rise (LCZ1) areas during daytime and nighttime respectively. Urban dwellers were easier exposed to serious heat environment in LCZ3 and LCZ1 areas over the north subtropical climate zone. Contrasts of CUHII and SUHII among different urban classes could exceed 1.7 °C and 5.4°C. The intra‐urban heterogeneity may alter the dominant factors controlling SUHII, which were also modulated by local climate and HW intensity. Unlike other controlling factors, the impact of local climate on the contribution from the urban‐rural contrast of convection efficiency was larger than urban features. Overall, CLM5‐LCZs displayed potential of implementing detailed simulations for inter‐ and intra‐city UHIs at a larger scale, and enhancing the capabilities in modelling urban climate and exploring the causes and controls of UHIs.

Biophysical Drivers of Seasonal Hysteresis of Urban Heat Islands Across Climates and Urban Landscapes

“…It is incorporated into the CLM5 (i.e., CLM5-LCZs), the land surface component of the CESM2, by which the biophysical processes of the coupled urban-biosphere system could be explored. As highlighted by Li et al (2023), the CLM5-LCZs did a reasonable job of simulating surface energy budget and thermal regimes in cities validated by observational fluxes from a flux tower measurement site and temperatures from automatic meteorological stations. The subgrid heterogeneity of the CLM5 consists of five land units: vegetated, lake, glacier, crop and urban, where physical state and flux variables are calculated separately with individual parameterizations but sharing identical atmospheric conditions over the same grid cell (Lawrence et al, 2018).…”

“…It is characterized by a distinctive monsoon system and a complex zonal climatic disparities that could be distinguished as the south subtropical (SS), mid subtropical (MS), north subtropical (NS), warm temperate (WT) and mid temperate (MT) climate zones according to Zheng et al (2010) (Figure 1a). To further interpret the impacts of background climates, the SS, MS and NS climate zones are aggregated as the subtropical climate referring to a humid climate (annual precipitation >800 mm), and the WT and MT climate zones are aggregated as the temperate climate corresponding to a semiarid climate (annual precipitation about 400∼800 mm), of which more details could be found in Li et al (2023). The model is first run for 10 years from 1999 to 2008 driven by the China Meteorological Forcing Dataset (CMFD), one of the most widely used high spatial-temporal resolution gridded climate data sets developed specifically for investigating land surface processes in China (He et al, 2020).…”

“…A newly developed urban canopy model based on the LCZs classification is utilized to simulate surface air and skin temperature, and other surface climate variables including surface heat or momentum fluxes in cities (Li et al, 2023). It is incorporated into the CLM5 (i.e., CLM5-LCZs), the land surface component of the CESM2, by which the biophysical processes of the coupled urban-biosphere system could be explored.…”

“…Additionally, the complex urban system, typically characterized by intra-urban heterogeneity, can also affect UHIs significantly by the changes in specific biophysical features. According to Li et al (2023), the contrasts of CUHI and SUHI intensity among different urban landscapes might exceed 1.7°C and 5.4°C. It remains largely unclear how urban landscapes alter the CUHI and SUHI hysteresis typologies.…”

Urban climate infrastructures for biodiversity (and people): urban planning ambitions that ecological research must engage with

“…In particular, the increase in artificial surfaces, built-up or impervious (e.g. roads and pavements), fragments the habitats of many species (LaPoint et al, 2015) and substantially alters the local climate perceived by people and organisms living in cities (Li et al, 2023;Wilby & Perry, 2006). This influence of urbanization on local climate was first documented in the 19 th century by Howard (1833), who described differences in temperature records between the city of London and the surrounding countryside.…”