Usage of the tool is simple. In order to assess the heat stress in the Klimaatbestendige Stad Tool/Adaptation Support Tool and to see the effect of interventions the user has to:
- Follow the project setup and draw and define at least one climate adaptation intervention
- Go to the tab in the restults panel, right of the map window
- Click on the button '‘CALCULATE HEAT STRESS’ / 'BEREKEN HITTESTRESS'
- Click the following buttons to see the results:
- PET new / PET nieuw - for situation after interventions
- PET difference / PET verschil - heat stress reduction
- PET current / PET huidig - for the PET situation before interventions
Description of urban heat stress calculation
To provide an indication of the Urban heat Stress in the public urban space, the AST presents the comfort temperature as PET (Physiological Equivalent temperature) index values in °C. In addition to this, AST presents the effect of interventions on reducing the PET.
PET is only one of many possible indicators for urban heat stress. In the Netherlands the PET has been chosen as one of the main indicators for urban heat stress and a standardized way to calculate this PET has been chosen and has been described by (Koopman et al., 2020). For all Dutch urban areas PET values, for a hot summer day, are freely available at www.klimaateffectlas.nl. The PET values presented are the average PET values from 12:00 until 17:59 for this summer day.
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).
Slight Cold Stress
No Thermal Stress
Slight Heat Stress
Moderate Heat Stress
Strong Heat Stress
Extreme Heat Stress (LV 1)
Extreme Heat Stress (LV 2)
Extreme Heat Stress (LV 3)
Extreme Heat Stress (LV 4)
For the AST 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.
- Large effect (PET reduction of 5 to 15 degrees)
- Medium effect (PET reduction of 2-5 degrees)
- Limited effect (PET reduction of 0.5-2 degrees)
- No effect
In fact, only the interventions with a large effect will ensure a reduction of the PET with at least one stress level (see Table 1).
The reason to classify the effect of interventions this way lays that only a few interventions (i.e. have a large effect on PET), some intervention have a reasonable small effect and others have no effect. The classification has been based on table 3.2 of (Kluck et al. 2020), which presents the effect of heat reducing interventions for urban areas.
The table below (OR LINK) shows the classification of the heat reduction of the interventions available in the AST.
PET reduction by .. %
Adding trees in streetscape
Bioswales (with drainage)
Building as levee
Cool building materials
Cooling with water elements: ponds
Create extra surface water (m2)
Deep groundwater infiltration
Ditch and swales
Drainage-Infiltration-Transport (DIT) drains
Drought resistant species
Extensive green roof
Extra intensive green roof
Floating puri-plants (floatlands)
Fountains, waterfalls, water facades
Green roofs with drainage delay
Improve soil infiltration capacity
Infiltration field and strips with surface storage
Lowering of terrace
Lowering part of garden
Permeable pavement (storage)
Permeable pavement systems (infiltration)
Private green garden
Rainwater detention pond (wet pond)
Rainwater storage below buildings
Remove pavement to plant green
Retention soil filter
Smart irrigation measures
Storage by creating extra freeboard
Storage tank or underground water storage
Systems for rainwater harvesting
Use of groundwater (aquifer storage and recovery)
Wetting surfaces (of gardens, roofs, roads)
AST 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 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 calculation steps are:
- Reading the PET values from a copy of the dataset with PET-values, which is available at klimaateffectatlas.nl (average PET values over 6 hours for specific hot summer day).
è for each raster pixel within project area: PET_local
- Assessment of the minimum PET value in the 2km2 surrounding the project area (including the project area). è PET_minumum
- For each raster point with an intervention define the maximum reduction factor of the PET: RF_PET. If interventions overlap only the maximum RF is applied.
- Calculate the PET reduction PET_reduction= (PET_local – PET_minimum) * RF_PET.
- The new pet for each raster pixel within project area PET_new = D_PET*RF_PET.
- The PET values for old and new situation are presented in color with indication of the different classes of heat stress.
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 AST.
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
Coccolo, S., Kämpf, J., Scartezzini, J. L., & Pearlmutter, D. (2016). Outdoor human comfort and thermal stress: A comprehensive review on models and standards. Urban Climate, 18, 33–57. https://doi.org/10.1016/j.uclim.2016.08.004
Epstein, Y., & Moran, D. S. (2006). Thermal comfort and the heat stress indices. Industrial Health, 44: 388. https://doi.org/10.2486/indhealth.44.388
Koopmans, S., Heusinkveld, B., & Steeneveld, G. (2020). A standardized Physical Equivalent Temperature urban heat map at 1-m spatial resolution to facilitate climate stress tests in the Netherlands. Building and Environment, 181, 106984. https://doi.org/10.1016/j.buildenv.2020.106984
Kluck, J., Lisette, E.J., Solcerová, A., Kleerekoper L.I., Wilschut, L., Jacobs, C.M.J., Loeve, R., (2020) De hittebestendige stad Een koele kijk op de inrichting van de buitenruimte, Hogeschool van Amsterdam, ISBN: 978-94-92644-80-0
Matzarakis, A., Muthers, S., & Rutz, F. (2014). Application and comparison of UTCI and PET in temperate climate conditions. Finisterra, 49(98), 21–31. https://doi.org/10.18055/Finis6453
Pilcher, J. J., Nadler, E., & Busch, C. (2002). Effects of hot and cold temperature exposure on performance: a meta- analytic review. Ergonomics, 40(10), 682–699. https://doi.org/10.1080/00140130210158419
Spanjar, G., Van Zandbrink, L. Bartlett, D. & Kluck, J. (2020). Cool Towns Heat Stress Measurement Protocol: Thermal comfort assessment at street-level scale. Amsterdam: Amsterdam University of Applied Sciences. Cooltowns.eu In press, future link