5 - WRF/UCM simulation for city-scale UHI modeling

Abstract

Recent haphazard urbanization and adverse impacts of climate changes are growing concerns in urban climate study. For this, the study of urbanization impacting on urban climate change is urgent to urban climatologists. To assess the different climatological processes in exchange of heat, momentum, and vapor content in built urban environment, an urban canopy model (UCM) is integrated to the weather research and forecasting (WRF) model. This model provides more precise level synoptic forecasting with improved lower boundary conditions for the simulated sites. This is single-layer model that allows reproduction of urban built environment with generalized urban structure and geometrical configuration. The WRF/UCM captures the shadow areas of building, reflected radiations (short and long), wind flow through canopy, and multilayer heat transfer for building roofs, concrete walls, and road pavement surfaces. In this chapter, the simulation examines climatological impacts of built urban environment in context of urban heat island (UHI) over the Kolkata metropolitan area (KMA) using dynamical downscaling with WRF/UCM. This is the first-time application of WRF/UCM in KMA areas for quantifying the impacts of urban land use and land cover (LULC) and anthropogenic heat release on urban climate and UHI effects. The results of the simulations have revealed two major outcomes: (1) simulated results reproduced by WRF/UCM and observations have a precise agreement in between, and (2) the nature and pattern of thermal heterogeneity of UHI are closely linked with impact of urbanization process and LULC changes. The results showed that agreement between simulated and observed data for T2m exhibits high capability of the WRF/UCM in simulation of UHI effects. In addition, results also show that swift urbanization has substantially changed the UHI effect over KMA region. In the diurnal scale, the UHI intensity is more complex in urban core than rural surrounds varying up to 3.55°C (mean UHI intensity around −0.09 to 1.55°C). These increasing temperatures are mainly occurred due to deforestation, conversion of cropland areas to built-up areas, which may increase the sensible heat transfer and decrease the latent heat transfer in newly developed urban areas in KMA. Moreover, the impact of old urban structure in UHI effects in the central KMA was estimated to be about 0.63°C, while recorded observed temperature increase is about 0.95°C for the simulation period.