Maximum extent of human heat stress reduction on building areas due to urban greening

Abstract

Based on the ENVI-met model v4.0 BETA, numerical simulations were carried out for five different sized building areas in the city of Stuttgart (Southwest Germany) on the heat wave day 4 August 2003. Human heat stress is primarily quantified by the physiologically equivalent temperature (PET). Additional background information is provided by both near-surface air temperature (Ta) and mean radiant temperature (Tmrt). The simulations concern five urban land use scenarios. Related to differences of simulation results between a scenario that only consists of asphalt surfaces and a green scenario only showing grasslands and trees, the resulting ΔTa, ΔTmrt and ΔPET values are interpreted as maximum extent of human heat stress reduction on the building areas by urban greening. To achieve a higher reliability for urban planning, the results are averaged over the period 10-16 CET. Exemplarily for one building area the results are presented in terms of grid-related absolute values. Besides mean absolute values for each building area whose magnitudes depend on the meteorological conditions of the simulation day, the results include mean relative ΔTa, ΔTmrt and ΔPET values. As verified by additional simulations for a current typical summer day, they can be regarded as representative for summer in Central Europe. Averaged over the five building areas mean ΔTa amounts to 1.1 °C (4%), mean ΔTmrt to 17.6 °C (26%) and mean ΔPET to 7.5 °C (16%). The results of further simulations point to the increase of human heat stress by the planning variants for the building areas compared to the maximum extent of human heat stress reduction by the green scenario. It reaches 0.4 °C (1%) for mean ΔTa, 4.9 °C (9%) for mean ΔTmrt, and 3.7 °C (9%) for mean ΔPET.