Future temperature and urban heat island changes in Budapest: a comparative study based on the HMS-ALADIN and SURFEX models

Abstract

Cities, due to their warmer and dryer local climate in addition to their dense population, are subjected to large future climate change risks. Land surface models, with detailed urban parameterization schemes, serve as an adequate tool to refine the rough regional climate projections over the cities. In this study, the future temperature conditions in Budapest are studied with the SURFEX land surface model (LSM), driven by the HMS-ALADIN5.2 regional climate model (RCM) and considering the high-emission RCP8.5 scenario. Special attention is dedicated to explore the differences between the RCM and LSM in terms of the results, their interpretation, and further use in impact models. According to the investigated model combination, the winter season may warm the most, with 1.9 °C in 2021–2050 and 4.3 °C in 2071–2100, although the magnitude of this change is smaller in SURFEX than in ALADIN. Besides the mean changes, four climate indices, based on high and low temperature thresholds, were studied, and it was found that the low temperature indices (frost days and very cold days) may relatively decrease more in SURFEX compared to ALADIN over Budapest, and in the city center compared to the suburbs and rural areas. In addition, the urban heat island (UHI) intensity is projected to decrease in SURFEX mainly in spring and summer (by 2071–2100 with 0.35 °C and 0.32 °C, respectively). Finally, a simple method is provided to correct the SURFEX temperature fields, using the ALADIN model, with eliminated systematic biases and the simulated UHI field.