...
To provide an indication of the Urban heat Stress in the public urban space, the AST CRCTool presents the comfort temperature as PET (Physiological Equivalent temperature) index values in °C. In addition to this, AST CRCTool presents the effect of interventions on reducing the PET.
...
The PET values give an indication of the heat stress people would be exposed to at each m2 of the urban area as presented in following table 1, which combines different levels of heat stress to PET values. The publication (Spanjar et al, 2020), [JK6] provides the following short introduction to explain PET:
| People experience heat stress when too much heat is absorbed by the body (Epstein & Moran, 2006). It can cause a decrease in mental and manual performance, have negative effects on social behaviour, cause heat exhaustion and heat stroke, and may even lead to death (Bell, 1981; Epstein & Moran, 2006; Pilcher et al., 2002). In humans it can be measured by the Physiological Equivalent Temperature (PET) index and this is the most commonly used climate comfort index when measuring outdoors (Coccolo et al., 2016; Matzarakis et al., 2014). The PET-index is expressed in degrees Celsius (°C). |
|---|
PET (°C) Physiological Stress Grade
Table 1: Ranges of the thermal index Physiological Equivalent Temperature (PET) for different grades of Thermal Perception and Physiological Stress on human beings (After Nouri et al. 2018, adapted from Matzarakis et al. 1999).
<18 | Slight Cold Stress |
18-23 | No Thermal Stress |
23-29 | Slight Heat Stress |
29-35 | Moderate Heat Stress |
35-41 | Strong Heat Stress |
41-46 | Extreme Heat Stress (LV 1) |
46-51 | Extreme Heat Stress (LV 2) |
51-56 | Extreme Heat Stress (LV 3) |
>56 | Extreme Heat Stress (LV 4) |
For the AST the CRCTool the choice was made to provide a rough indication of the effect of interventions on reducing the PET. For the purpose the interventions have been classified in three (or four) classes.
...
The table below (OR LINK) shows the classification of the heat reduction of the interventions available in the ASTCRCTool.
ID | Adaptation Interventions | PET reduction by .. % |
3 | Adding trees in streetscape | 75 |
72 | Bioretention cell | 10 |
6 | Bioswales (with drainage) | 10 |
88 | Building as levee | 0 |
62 | Cool building materials | 10 |
8 | Cooling with water elements: ponds | 10 |
19 | Create extra surface water (m2) | 10 |
80 | Creating shadow | 75 |
10 | Deep groundwater infiltration | 0 |
11 | Ditch and swales | 10 |
20 | Drainage-Infiltration-Transport (DIT) drains | 0 |
84 | Drought resistant species | 0 |
15 | Extensive green roof | 10 |
12 | Extra intensive green roof | 10 |
13 | Floating puri-plants (floatlands) | 10 |
7 | Fountains, waterfalls, water facades | 25 |
82 | Gravel layer | 0 |
14 | Green facades | 10 |
16 | Green roofs | 10 |
42 | Green roofs with drainage delay | 10 |
51 | Improve soil infiltration capacity | 0 |
33 | Infiltration boxes | 0 |
22 | Infiltration field and strips with surface storage | 10 |
23 | Infiltration trenche | 10 |
24 | Infilttration shafts | 0 |
81 | Levees | 0 |
45 | Lower streets | 0 |
92 | Lowering of terrace | 0 |
93 | Lowering part of garden | 0 |
90 | Permeable pavement (storage) | 0 |
26 | Permeable pavement systems (infiltration) | 0 |
27 | Private green garden | 25 |
87 | Quay | 0 |
29 | Rain barrels | 0 |
95 | Rain gardens | 10 |
71 | Rainwater detention pond (wet pond) | 10 |
30 | Rainwater storage below buildings | 0 |
91 | Remove pavement to plant green | 10 |
31 | Retention soil filter | 0 |
83 | Small quay | 0 |
57 | Smart irrigation measures | 0 |
32 | Storage by creating extra freeboard | 0 |
46 | Storage tank or underground water storage | 0 |
35 | Surface drains | 0 |
37 | Systems for rainwater harvesting | 0 |
89 | Temporary levee | 0 |
39 | Urban agriculture | 10 |
25 | Urban forest | 75 |
94 | Urban parks | 75 |
4 | Urban wetland | 25 |
53 | Use of groundwater (aquifer storage and recovery) | 0 |
40 | Water roof | 10 |
41 | Water square | 0 |
61 | Wetting surfaces (of gardens, roofs, roads) | 25 |
Calculation background
AST CRCTool uses the calculations steps below to asses the PET values in a raster of 2*2m2 in the project area. Roofs and water are excluded from the calculations, as people are not expected to be there. To provide a logical outcome while keeping the required calculations simple, AST CRCTool calculates for each raster pixel the differences between the local PET value and a local minimal PET value (in an area of 2km2). For the raster pixels at which an intervention is planned, this PET difference is multiplied with the expected reduction factor (see table). This gives the expected PET reduction in °C. This methodology was chosen in order to calculate in a simple way the effect of interventions which would overlay earlier heat reducing features or cooler situations (like shadow of existing trees/buildings and existing green), without presenting a double effect of the old and new interventions.
...
The results for overlapping and non-overlapping interventions and for interventions overlapping current head reducing features appear logical. In some situations, old heat reducing features (like the shadow of building) might be slightly visible in color differences, but they result only in small differences (up to several degrees) as compared to the 6 °C PET-difference between two classes of heat stress. Users should understand the simplicity of the model and the fact that only rough estimations of heat stress reduction can be given as the effect of the interventions on the PET is also dependent on many local characteristics and situation of the people who should feel the difference in comfort temperature. Such local information is not available nor part of the PET map which is used as input for the PET in the ASTCRCTool.
References
Bell, P. A. (1981). Physiological, Comfort, Performance, and Social Effects of Heat Stress. Journal of Social Issues, 37(1), 71–94. https://doi.org/10.1111/j.1540-4560.1981.tb01058.x
...