Assumptions & limitations for heat stress

This section describes the main assumptions and limitations for the provided datasets (see Data access).

The maps mainly provide information on outdoor heat exposure and related aspects. Maps for indoor exposure still need to be developed. The map with perceived temperatures gives an indication of the impact of meteorological conditions on a person outdoors, without activity, but does not provide insight into other impacts of heat or into indoor temperatures. National maps providing insights into indoor heat exposure are still limited.

One of the key limitations of the Urban Heat Island (UHI) effect map is that it only presents annual average temperature differences, without capturing extreme temperature events. During periods of extreme weather, urban temperatures can rise significantly above these averages, potentially leading to more severe impacts than the map suggests.

When using the Distance to Cooling map, take into account that the current version is based on an earlier version of the perceived temperature map, which may affect accuracy. An update to the methodology is needed to improve the results.

Other remarks are mentioned in the technical notes (PDF), and include:

• Small cool spots may be missed if too fragmented.
• Only public green spaces are included, and private gardens are excluded.
• Analysis is limited to urban areas, based on Topographic Nederland (1:10.000) excluding rural zones.
• Some spots may be inaccessible due to vegetation.
• Narrow shapes are excluded, though they might still offer cooling.
• Weather data from one day may skew results, especially in the north.
• Distance calculations may be off due to missing or misclassified paths.
• Building entrances are assumed to be on the road, which may distort walking distances.

The map Shaded footpaths and cycle tracks only shows separate cycle tracks. Cycle lanes on roadways are not listed on the Basic Registration of Large-Scale Topography (BGT) and thus not reflected on the map. Also, the shade was calculated for 3.30 PM, as statistically this is the hottest time of the day, however this is subject to the weather on the specific day. The selected date and time of day are in line with the points of departure set out in the Benchmark for Green Climate Adaptive Built Environment, and are comparable with the points of departure underpinning the Perceived temperatures heat map.

The maps with warm evenings and nights show how often average evening and nighttime temperatures exceed 20 °C and 24 °C in the current climate. They do not show how the frequency of warm evenings and nights may change under future climate conditions and therefore do not provide future scenarios. The maps provide insight into regional differences in warm evenings and nights, but do not show precisely how much warmer urban areas are compared to their surroundings.

The Shade on buildings map shows the average amount of shade on building façades from surrounding trees and buildings. Shade is calculated for four moments in time (8:00, 12:00, 16:00 and 20:00) on June 21st and combined into one score per building block. The map only considers shade from the surroundings and does not include other factors that influence indoor temperatures, such as window size and orientation, sun shading, ventilation and other building characteristics. It should therefore be regarded as an indication of the risk of overheating rather than a measure of actual indoor temperatures.

The Social vulnerability to heat map provides an initial indication of social vulnerability based on two indicators: the proportion of over-65s in frail health and the proportion of households living around or below the social minimum. These indicators do not provide a complete picture of social vulnerability to heat. Other relevant factors, such as loneliness, limited mobility and severe obesity, are not included. The map should therefore be used as a starting point for identifying potentially vulnerable neighbourhoods rather than as a comprehensive assessment of social vulnerability to heat.