Identification of current and emerging drivers of heat risk in the UK to inform interventions which prioritise equity.

Background: The climate is warming with hotter summers and periods of extreme heat projected to become more prevalent globally. High ambient temperatures have been associated with excess mortality in the UK, with older adults in particular at elevated risk. Heat exposure is a growing threat to public health in the UK due to projected climate change and an ageing population. This thesis identifies and explores drivers of heat risk at the population, neighbourhood and household level for the UK. This includes existing and emerging drivers. Understanding the drivers of increased heat-risk will inform targeted and effective interventions which improve health outcomes whilst reducing inequities. The focus is on equity as those most impacted by climate change are often those least able to adapt.

Methods: At the population level a semi-systematic (conducted by a single reviewer) literature review assessed the inclusion and impact of population change in heat health projections. The review covered both population growth and changes in population structure. A health impact assessment was then implemented, extending the existing work in this topic to include socioeconomic development. Exposure response coefficients were calculated for the observed period (1981-2020) and then modified based on a number of pathways set out in the UK-SSP project. At the neighbourhood level, drivers were identified through a number of existing literature reviews and key papers. Data at high spatial resolution for each driver was acquired and the distributions of these drivers explored to assess inequalities in heat risk. A diagram informed by systems thinking was developed as an initial mapping. From this systemic inequalities were identified and interventions which seek to prioritise equity whilst improving health were proposed. At the household level, building stock modelling using a meta-model was used to estimate indoor temperature and air quality across the UK. Air quality is included here as an environmental exposure which co-occurs with heat and should be considered alongside overheating when planning dwelling improvements. Inequalities in exposure due to housing were assessed using paired data from the most recent census to inform building level interventions aimed at reducing inequalities.

Results: The semi-systematic literature review identified papers aiming to project the heat-health burden. The review found 45% included changes in population size and 23% changes in age structure. On average, non-inclusion of changes in population lead to underestimation of health burdens of 64%. The health impact assessment found significant increases in heat-related mortality under high emissions scenarios, with the highest burden observed in the RCP8.5-SSP5 scenario, due to combined high temperatures and population growth. The lowest burden is seen under RCP2.6-SSP1, reflecting effective adaptation and lower warming levels. Regional variations and the impact of potential power outages during heatwaves were also examined, highlighting the role of adaptation and resilience in estimating the future heat health burden. The main driver, out of climate, population and adaptation, was dependent on both the scenario and region considered. Inequalities were found across a number of indicators relating to heat exposure, vulnerability, and adaptive capacity. This included inequalities in urban greening and access to greenspace, physical and mental health and access to communication and support. Each of these factors had been identified as a heat risk factor in the existing literature. Barriers to the effective implementation of adaptation strategies were identified and informed recommendations on the implementation of interventions. Maximum indoor temperature was found to be higher in areas with larger ethnic-minority and infant populations. This coincided with higher indoor concentration of outdoor-source air pollution (PM2.5) in areas with larger ethnic-minority populations. These findings suggest housing and environmental conditions play a key role in generating health inequalities from social disadvantage.

Conclusion: This thesis has identified and quantified key drivers of the heat health burden and heat risk at a range of spatial levels. These are climate change and population growth and ageing at the population level, and an unequal distribution of risk factors at the neighbourhood and building level which result in inequities in heat risk. This makes a clear case for comprehensive adaptation plans in relation to increased heat exposure due to climate change and the importance of equity considerations within these plans. For example, population level initiatives should support healthy ageing, neighbourhood level incentives must aim to build capacity within the community to support vulnerable individuals and building level improvements to include low-income renters.