Modelling the risks of urban heat islands for the ageing society

Abstract

Heat waves are a leading cause of weather related fatalities world-wide. Due to increasing urbanisation, climate change and an ageing population, health risks for urban populations will continue to increase in the coming years. The effect of urban heat islands on the health of vulnerable groups where especially the elderly population is hit the hardest, is widely recognized in literature. In past studies the effect of heat has been modelled for the entire population of a city or state where outside temperature measures or land surface temperature is the hazard. Research on specific vulnerable groups such as the elderly is relatively sparse to this date. In this study various datasets have been combined with the aim of providing a method for the development of a heat-related elderly risk index (HERI) for the elderly population of The Hague. The final composite risk indexes have been constructed for three moments in the day on the 27th of July which was the hottest day of the heat wave of 2018. The structure of the index is based on Crichton’s Triangle of Risk, which states that risk is a function of hazard, exposure, and vulnerability. By selecting the following indicators to represent the spatial layers: physiological equivalent temperature, indoor temperature, facade orientation, being 75 years or older, loneliness among people over the age of 75, and population density. The indicators are assigned a weight trough the Analytical Hierarchy Process (AHP), after which the indicators can be combined into a HERI maps for the three timestamps. Different configurations of indicators have been used for creating the HERI maps, yielding different weights for each set. This resulted in two types of HERI maps: HERI-2 and HERI- 3. HERI-2 exists of physiological equivalent temperature, being 75 years or older, loneliness among people over the age of 75, and population density. HERI-3 is composed of the same indicators as HERI-2 but instead of physiological equivalent temperature, indoor temperature is used as the hazard. The HERI maps for the three timestamps have been validated by performing a Pearson Correlation between the HERI maps and the mortality numbers among the elderly in the days after the heat wave. The indicators and mortality are non correlated except for the indicator ’being 75 years or older’. However when the indicators are combined into the HERI index maps a weak positive correlation with mortality can be seen. The results indicate that it is necessary that the indicators have to be re-evaluated and several weighting methods have to be considered in order to improve the HERI.