Surface urban heat island characteristics in Budapest (Hungary) during the summer period

Budapest is the capital and the largest city of Hungary, with 1.7 million inhabitants, surrounded by a large agglomeration area. Using a 20-year surface temperature database measured by NASA's Terra and Aqua satellites, we analysed the spatial distribution, inter-annual variability and 20-year trends of the urban surface heat island in Budapest. As the presence of the urban heat island causes the most adverse effects in summer, we investigated the evolution of surface temperature and heat island intensity in details for the late spring and summer months, with a special focus on heat waves.

Our results show that the maximum surface heat island intensity usually occurs in June, during the daytime. It was found that during the studied months, the monthly average surface temperature in the urban area exceeds 30 °C in the early afternoon and approaches 40 °C in the summer months of the hottest years. During periods of intense heat waves, surface temperatures above 50 °C can be detected on some days in a large area of the city. Our studies show that in dry, heat-wave weather situations, when surface temperatures are extremely high, relatively low heat island intensities occur. In these cases, the lower heat island intensities are not caused by a decrease in urban surface temperatures, but by a more intense warming of the areas outside the city, which is a consequence of the lower latent heat content of the energy balance above natural surfaces in these hot, dry situations.

As the Intergovernmental Panel on Climate Change (IPCC) assessment report states, extreme weather events, including heat waves, will become more frequent, longer, and more intense as global warming increases, therefore, it is important to gain a better understanding of the urban heat island effect to help developing effective climate adaptation strategies on local/regional scale.