High resolution simulation of Stockholm's air temperature and its interactions with urban development

Stockholm is expanding fast in response to increasing housing needs. This paper evaluates the consequences of land-use changes on summer temperatures. Urban development scenarios for 2030 and 2050 were developed together with the municipality. The spatial and temporal variations of the changes in the urban air temperature are simulated at 1 km grid resolution applying a dynamical downscaling technique. The comparison against observations obtained during 5 years at 11 weather stations shows that the high resolution model captures the dynamics of the intra-urban air temperature gradients with good performance skills. Scenario results indicate that the temperature of summer 2014 would increase over the new built-up areas by, on average, 0.29 °C in 2030 and 0.46 °C in 2050, up to a local maximum of 1.35 °C in the latter, as a consequence of urbanization. The number of days with temperature above the 75th percentile for the summer months increases by up to 10, with locations closer to the sea being less prone to temperature maxima. The spatial coverage of this warming effect is predominantly local, occurring mostly over the transformed/densified area. Better knowledge on how urban temperatures are affected by on-going urbanization is needed also in high latitude cities