Abstract
Abstract. Mean radiant temperature (Tmrt) is a frequently used measure of outdoor radiant heat conditions. Excessive Tmrt, linked especially to clear and warm days, has a negative effect on human wellbeing. The highest Tmrt on such days is found in sunlit areas, whereas shaded areas have significantly lower values. One way of alleviating high Tmrt is by planting trees to provide shade in exposed areas. Achieving the most efficient mitigation of excessive Tmrt by tree shade with multiple trees requires optimized positioning of the trees, which is a computationally extensive procedure. By utilizing metaheuristics, the number of calculations can be reduced. Here, we present TreePlanter v1.0, which applies a metaheuristic hill-climbing algorithm on input raster data of Tmrt and shadow patterns to position trees in complex urban areas. The hill-climbing algorithm enables dynamic exploration of the input data to position trees, compared with very computationally demanding brute-force calculations. The hill-climbing algorithm has been evaluated with a static greedy algorithm that positions trees one at a time based on ranking and is expected to always find relevant locations for trees. The results show that the hill-climbing algorithm, in relatively low model runtime, can find positions for several trees simultaneously, which lowers Tmrt substantially. TreePlanter, with its two algorithms, can assist in optimization of tree planting in urban areas to decrease thermal discomfort.
Highlights
The increased risk of exposure to excessive heat in urban areas during extreme events as an effect of a modified urban climate can lead to excess mortality and morbidity (Dousset et al, 2010; Gabriel and Endlicher, 2011)
TreePlanter make use of output data generated by the SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model (Lindberg et al, 2008)
This section gives a short summary of the model in chronological order: 1. SOLWEIG is executed for a given number of time steps based on meteorological data and other necessary gridded input data to simulate Tmrt (Tmrt.solweig) and shadow
Summary
The increased risk of exposure to excessive heat in urban areas during extreme events as an effect of a modified urban climate can lead to excess mortality and morbidity (Dousset et al, 2010; Gabriel and Endlicher, 2011). Tmrt is the sum of all short- and longwave radiation fluxes (both direct and reflected) to which the human body is exposed, defined by ASHRAE (2001) as the “uniform temperature of an imaginary enclosure in which radiant heat transfer from the human body equals the radiant heat transfer in the actual nonuniform enclosure”. Thorsson et al (2014) showed that there is a higher correlation between Tmrt and mortality compared than between air temperature and mortality on hot days. High daytime Tmrt correlated with heat related mortality among people aged 80+, whereas high nighttime Tmrt correlated with heat related mortality among peopled aged 45–79
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