The development of a vulnerability index for communicating heat risk information

An essential element for climate risk communication and management is availability of information related to the spatial distribution of risk which is dependent on the spatial characteristics of a given extreme climate event and the location of vulnerable groups. In the case of extreme heat events in large cities, the spatial distribution of risk is most likely related to the interaction of intra-urban heat anomalies and the location of individuals possessing multiple heat risk factors. A pressing issue in environment and hazards research is how to describe, measure and present vulnerability for natural hazard risk assessment, communication and management. This paper takes up this challenge for the case of the heat wave hazard in large cities and describes the development and testing of a heat vulnerability index for London. UK. The a priori heat vulnerability index, which is based on a range of generic heat risk factors and developed using Principal Components Analysis, when mapped provides an insight into London's heat vulnerability landscape. The index potentially provides a tool for communicating to a number of stakeholders in the heat risk problem information about the spatial variation of heat risk. Clearly the credibility of any such tool for communicating and managing risk will be dependent on the its efficacy in terms of being able to differentiate between areas of actual low and high heat related health outcomes. Accordingly the results of a test of the utility of the vulnerability index for predicting the spatial variation of heat related health outcomes will be presented in this paper. As a basis for the test of efficacy the following hypothesis is examined “the heat vulnerability index is able to predict the spatial variation of mortality and ambulance callouts during heat events”. To test this hypothesis a data set comprising daily temperature, mortality and ambulance callout data was assembled. This paper will present this data, as well as the criteria applied to the identification of heat events and discuss the methodology applied in developing the heat vulnerability index and testing the aforementioned hypothesis. Evaluation of the vulnerability index reveals that when qualitatively compared with the morphology of the surface urban heat island, as expressed by the spatial variation of surface temperature, it is clear that areas of high heat exposure and high vulnerability overlap. Quantitative testing of the vulnerability index using ANOVA, Poisson Regression and Binary Prediction reveals that it may be possible to model where hot spots of vulnerability, in terms of increased mortality and a higher number of ambulance callouts, occur. The paper will conclude by discussing the advantages and disadvantages of the heat vulnerability index for managing and communicating heat related risk in large cities.