U.K. Climate Projections: Summer Daytime and Nighttime Urban Heat Island Changes in England’s Major Cities

Abstract

In the UK where 90% of residents are projected to live in urban areas by 2050, projecting changes in urban heat islands (UHIs) is essential to municipal adaptation. Increased summer temperatures are linked to increased mortality. Using the new regional UK Climate Projections, UKCP18-regional, we estimate the 1981–2079 trends in summer urban and rural near-surface air temperatures, and UHI intensities during day and at night in the 10 most populous built-up areas in England. Summer temperatures increase by 0.45–0.81°C per decade under RCP8.5, depending on the time of day and location. Night-time temperatures increase more in urban than rural areas, enhancing the night-time UHI by 0.01–0.05°C per decade in all cities. When these upward UHI signals emerge from 2008–2018 variability, positive summer nighttime UHI intensities of up to 1.8°C are projected in most cities. However, we can prevent most of these upward night-time UHI signals from emerging by stabilising climate to the Paris Agreement target of 2°C above pre-industrial levels. In contrast, daytime UHI intensities decrease in nine cities, at rates between -0.004 and -0.05°C per decade, indicating a trend towards a reduced daytime UHI effect. These changes reflect different feedbacks over urban and rural areas and are specific to UKCP18-regional. Future research is important to better understand the drivers of these UHI intensity changes.

Climate change projections for sustainable and healthy cities

“…There is, however, an indication of enhanced warming of minimum temperature (which can be considered as the night-time temperature) over the Central London region (Figure 3). Some enhancement of the nocturnal UHI is also seen in the driving 12 km RCM simulations (Eunice Lo et al 2020). This finding differs from earlier studies with coarser and simpler models that indicate little or no change in the average London UHI (Lauwaet et al 2015;McCarthy et al 2011).…”

“…To be effective over the coming decades, green and/or blue space (a priority for London), for example, should be designed to be resilient to a changing climate. In selecting the most appropriate tree species to plant in London currently, for example, consideration should be given to their ability to cope with hotter conditions (Eunice Lo et al 2020), as well as more variable rainfall and generally drier summers (Jacob et al 2014). Similarly, green roofs and drainage systems need to be designed to cope with projected increases in rainfall intensity during convective storms (Kendon et al 2019).…”

“…temperatures at rural reference stations may rise faster than in already heavily urbanised areas due to larger relative changes in the urban fraction in rural areas in recent decades. Some of the first modelling studies that attempted to incorporate the UHI in climate projections indicate that any increase in the average UHI intensity may be limited and, in some cases, might even decrease in relative terms (Eunice Lo et al 2020;Fischer et al 2012;Lauwaet et al 2015;McCarthy et al 2011;Oleson 2012). These studies highlight the need for more detailed modelling focusing on a larger range of cities in different climatic regions.…”

“…Multi-model RCM ensembles of varying size have been produced for domains covering most of the globe, including Europe(Jacob et al 2014), Africa(Nikulin et al 2018) and East Asia(Niu et al 2018) as part of the Co-Ordinated Regional Downscaling Experiment (CORDEX).5 The standard CORDEX simulations are forced by outputs from CMIP5 GCMs and have a grid-box resolution of between 50 km (0.44° latitude/longitude) and 12 km (0.11° latitude/longitude), with outputs freely available. The CORDEX and other RCM simulations are widely used to explore the impacts of climate change, including those in cities(Abiodun et al 2017;Eunice Lo et al 2020).…”

Climate Resilience of Internally-Insulated Historic Masonry Assemblies: Comparison of Moisture Risk under Current and Future Climate Scenarios

“…In this study, Met Office weather stations and UKCP18's local projections allowed for the use of weather data collected in an urban centre. Although its high-resolution grid captures urban land use and subsequent urban heat island (UHI) effect in major cities such as London used in this study [49], wind is a variable further nuanced by microclimate. DELPHIN's rain model for this study is not comprehensive enough to account for microclimate nuances such as adjacent buildings or obstructions.…”