Heat Extremes and Urban Climate Dynamics in Andean cities

Complex interactions between the urban and regional climatic processes occur in Andean cities. These are shaped by the mountainous topography and increasing urbanization, resulting in significant environmental challenges. Climate change is leading to an increased intensity and frequency of meteorological extremes, increasing the risks in these fragile urban environments. Extreme and unusual heat events in the Andes have become a pressing issue in recent times, compounded by other climate extremes like prolonged droughts and intense rainfall. This has resulted in severe impacts such as glacier loss, water shortages, extreme floods and unbearable thermal stress for local communities, especially in cities. This study examines the microclimatic variations across four Andean cities – Bogota, Cusco, La Paz and Santiago, during recent extreme heat episodes, using WRF (Weather Research and Forecast) simulations. The ERA5 reanalysis data is used to define the initial and boundary conditions of the WRF model, calibrated to represent climatology of the entire Andes region. To configure the urban morphology more accurately into the model, it is coupled with 3D urban canopy models, which are integrated with Local Climate Zones of each city generated through World Urban Database and Access Portal Tools. The modelled finer scale near surface meteorological parameters – temperatures (air and surface), wind flow patterns, relative humidity that are most relevant to determine the heat stress are analysed to understand the nature of micro-scale UHI (urban heat island) variations in each city. The results indicate how urban design and geometry influence the spatial variations in UHI for both large and medium-sized cities, during regional-scale heat extremes. This study presents the initial assessment to understand the dynamic interplay between urban microclimate and regional meso-scale climate and how it influences localised impacts of different meteorological extremes in the context of changing climate and urban development across this complex terrain.