Heat wave risk assessment in Bologna using Spatio-temporal artificial intelligence: Leveraging LSTM enhanced by the hippopotamus optimization algorithm

This study proposes a spatio-temporal machine learning framework that integrates a Long Short-Term Memory network with the nature-inspired Hippopotamus Optimization Algorithm for Heat Wave Risk (HWR) assessment in Bologna, Italy, where HWR refers to the combined threat posed by the intensity, frequency, and duration of extreme heat events and their impact on exposed and vulnerable populations. We utilized environmental, infrastructure, and demographic data spanning from 2014 to 2023. The heat wave model was developed using 14 key factors covering hazard, exposure, and vulnerability under Representative Concentration Pathways (RCPs) 4.5, 6.0, and 8.5. Inspection of the results revealed temperature, distance to public transportation, local climate zone, and Enhanced Vegetation Index (EVI) as critical factors influencing HWR. Performance evaluations employing statistical indices and a confusion matrix affirm the model's robust predictive capabilities. The developed model accurately distinguished between risk categories, achieving class-wise accuracies of 77.76 % for the 'Very Low' risk class and 78.72 % for the 'High' risk class, both of which were considered satisfactory. The Partial Dependence Plot approach is employed to interpret the behavior of the developed machine learning model, revealing that high temperatures, high relative humidity, limited vegetation cover, and increased distance from critical services such as healthcare and public transportation strongly influence the predicted HWR. Notably, projections under RCP 8.5 predict a significant increase in 'Very High' risk areas from 34 % in 2023 to 65 % by 2050. The study also confirms that enhancements in EVI and reduced proximities to green areas significantly mitigate HWR. These results emphasize the importance of incorporating targeted green infrastructure in urban planning to enhance resilience against heat waves, providing essential insights for urban planners and policymakers.