The challenge of heat stress in urban areas: A case study in the Merwede Canal Zone, Utrecht

Abstract

Global warming has increased the global surface temperature with 0.8° since pre-industrial values. The increase in surface temperature is not linear over time as two third of the warming has occurred since 1975. Moreover climate change is expected to increase both mean and extreme temperatures as heat waves become more intense, longer lasting, and occur more frequently.

Urban areas are more sensible to the temperature increase during heat waves due to the Urban Heat Island (UHI) effect. The UHI effect acts invigorative as temperatures in urban areas are significantly higher compared to rural areas. This effect is mainly due to urban characteristics; therefore this master thesis research project aims to efficiently reduce the heat stress in the Merwede Canal Zone in the city of Utrecht.

However there is no formal way to express heat stress in urban areas as there is no commonly used standard for heat stress. This research uses a new approach by the use of UHI24h and UHImax. The UHI24h represents the average urban heat island effect over one day cycle (24 hours). Where, the UHImax represents the massive heat at night which is the maximum value of the urban heat island effect in a 24 hour cycle. The heat stress in urban areas has been assessed by creating recommended scenarios with different adaptive cooling strategies. The different adaptive cooling strategies focus on the implementation of more green area and on changing the albedo of roofs, walls and roads. The adaptive cooling strategies are created within the UCAM (Urban Climate Assessment & Management) method which enables to simulate both the UHI24h and UHImax on a spatial scale.

The multiple adaptive cooling strategies are combined with an SCBA RAS (Social Cost-Benefit Analysis Rotterdam Climate Adaptation Strategy) in order to add a financial dimension to the strategies and to conclude which strategy is most efficient to reduce heat stress in urban areas.

This research showed that the implementation of green area mainly impact the urban heat island effect at night-time. While the implementation of different albedo types more likely change the urban heat island effect during the day. Hereby the most efficient strategy is the implementation of green measures as it is the most climate-robust solution which impacts on multiple levels at relative low costs. This research contributes to the current risk dialogue on what value is ‘’acceptable’’ for heat stress as it uses a new approach with the use of two components to express heat stress in urban areas.