Abstract Summary
Heat stress poses a serious threat to public health by causing symptoms ranging from mild discomfort, loss of labour productivity, sleep deprivation, to serious heat illnesses with possible (premature) death. Summer heat that causes heat stress is intensified especially at night in urban areas, and is projected to become more extreme due to climate change. Due to urbanization and the changing climate, more and more people will suffer from heat stress inside their homes. It is therefore important to understand heat stress indoors. However, observational and modelling studies on this aspect are relatively scarce, especially when it comes to the interconnections between indoor and outdoor climatic conditions. This study aims to observe, understand and model the behaviour of indoor air temperature during Dutch summer heat using two unique datasets. The first dataset consists of long measuring records up to 27 years of citizen weather stations (CWS) located in seven residences across the Netherlands. The second dataset consists of indoor CWS that were placed by us in almost 100 residences across Amsterdam in 2022 or 2023. As a proof of concept, we first analyse the first dataset of up to 27 years. We find that indoor temperature typically warms up more slowly, but also cools down more slowly than outdoor temperature with a lag difference of ~260 minutes in the diurnal cycle during summer. We demonstrate that nighttime indoor human thermal comfort (HTC) can be worse than outdoor HTC even for days after a heatwave. To model indoor temperature behaviour, we simulate six-hour changes in indoor temperature behaviour with a physics-based statistical model by Vant-Hull et al. (2018) that has an outdoor conduction, indoor conduction and solar transfer component. Preliminary results of this computationally-fast model for the seven houses are promising, with on average a mean absolute error of 0.43 K/day during summer. In the next research step, we scale up our proof-of-concept analyses to the ~100 indoor CWS placed in Amsterdam. These CWS measure the indoor climate – temperature, relative humidity, CO2 concentrations – in the bedroom and living room from the moment of installation until 2026. As each residence is unique, the results of the ~100 indoor CWS will give us a good insight into the statistical variation in the relationships between indoor and outdoor temperature, and in the model performances. Based on our insights, we plan to make recommendations for climate-sensitive urban design to reduce indoor heat stress.
