Urban microclimates have a great impact on the thermal comfort of city inhabitants, with the Urban Heat Island (UHI) and the Subsurface Urban Heat Island (SUHI) effects posing a growing challenge under the accelerating impacts of climate change. This thesis focuses on investigating the UHI and SUHI effects and exploring potential mitigation strategies within a controlled urban environment, specifically the ”Heat Square” at The Green Village in the Delft University of Technology. The Heat Square serves as an experimental urban environment designed to analyse various urban cooling measures. To capture the spatial and temporal variations in soil temperature within the Heat Square, Distributed Temperature Sensing (DTS) technology was deployed. DTS measures high-resolution temperature data, which allows for detailed analysis of the soil temperature response to different cooling scenarios, including the implementation of green infrastructure, shading, and reflective surfaces. These in-situ measurements were then compared with urban microclimate modeling results using ENVI-met, a Computational Fluid Dynamics (CFD) tool for modeling urban microclimatic conditions. ENVI-met, along with other urban microclimate models, can predict the impact of urban design on local temperature and thermal comfort indices. The findings of this research highlight the significant potential of green infrastructure and shading as effective strategies to mitigate the UHI effect. Specifically, the introduction of vegetation and shading elements resulted in noticeable reductions in both surface and air temperatures as well as Mean Radiant Temperature (Tmrt) within the urban environment. These findings were supported by performing simulations of different urban scenarios of the Heat Square. However, the study also highlighted challenges in accurately modeling urban microclimates, as shown by discrepancies between the DTS measurements and ENVI-met simulations. These differences suggest the need for further refinement of model parameters to better approximate the complexities of real-world urban environments. Overall, this thesis contributes to the broader understanding of urban cooling measures and their role in enhancing the resilience of cities to climate change. The insights gained from this research are intended to inform urban planning and design practices, promoting the development of more sustainable and climate-resilient urban spaces as well as the applicability of urban microclimate monitoring tools. Future research should focus on refining the ENVI-met model of the Heat Square to enhance its accuracy in properly simulation real-life responses of the urban environment to climatic variations. Additionally, exploring a broader range of urban cooling strategies, including water-based solutions and varying surface materials, could broaden knowledge on heat mitigation strategies. Studying soil thermal responses in other urban environments with DTS would also be valuable for studying indirect effects of the SUHI effect. Collaborations between researchers, urban planners, and policymakers are important to ensure that scientific findings are translated into practical applications that increase climate adaptability of urban environments.

Evaporation, the transformation of liquid water to vapor, plays a crucial role in forested ecosystems by contributing significantly to the total evaporation through interception evaporation and transpiration. This process is critical in climate models used to forecast both immediate and long-term climatic changes. Yet, accurately measuring and partitioning evaporation in forests presents challenges due to the complex interplay of factors like canopy height and density, vegetation type, and soil characteristics. Properly segmenting total forest evaporation into its key components—interception evaporation, transpiration, and soil evaporation—is vital for enhancing hydrological and climate modeling. Simplifications in current global climate models, such as GLEAM or the EC-Earth3 used by the Royal Netherlands Meteorological Institute, often overlook the essential role of interception evaporation, focusing mainly on transpiration. This research examines a way to partition total evaporation into its fundamental segments. The study’s main objectives were to partition total evaporation into interception evaporation and transpiration, and further into canopy and forest floor interception evaporation. This was accomplished using
three methodologies: 1) Eddy Covariance (EC) systems positioned above the canopy to measure
total evaporation, with leaf wetness sensors distinguishing between wet and dry canopy states; 2) Analysis of leaf wetness data to quantify canopy interception evaporation; 3) The Bowen Ratio Energy Balance (BR-EB) method to assess overall evaporation and its split into canopy and forest floor components. Selected case days for analysis included scenarios following rain and dew events, with selection criteria based on minimum evaporation thresholds and weather conditions.
Results underscored the significant roles of transpiration and interception in total evaporation,
affected by environmental dynamics and sensor placement. Notably, sensors at higher canopy levels indicated faster drying and lower interception to transpiration ratios due to increased exposure to environmental factors. Despite employing diverse methodologies, the research did not uncover uniform patterns in evaporation partitioning, pointing to the intricate relationships between environmental conditions and canopy structure. The study pinpointed methodological constraints, such as in the assumptions related to leaf wetness sensor data, which might skew evaporation calculations. Future studies should integrate additional measuring techniques, like sap flow sensors and enhanced BR-EB methods, to improve data accuracy and deepen understanding of forest evaporation dynamics.

This research addresses the issue of rising soil temperatures, driven by climate change. As the Drinking Water Distribution System (DWDS) is located in the sub-surface, the drinking water temperature in the distribution mains attains this rising soil temperature. Because the temperature of drinking water is an important determinant of water quality, Dutch law mandates that drinking water temperature may not exceed 25 °C. This study assesses several measures, including their quantitative impact on soil temperature reduction, and consequently on drinking water temperature reduction. These measures center on modifying the ground coverage, as this measure can be implemented without excavation and disrupting existing infrastructure in the sub-surface. This includes different types of ground coverage (e.g. changing concrete tiles, which are the existing top layer type, to vegetation), and creating temporary shade or applying white paint to the existing coverage type. The effect of (re)locating pipes to a deeper level or in the shade are also considered. The effect at the depth of a distribution main is analysed, which is shallow (0.7 m) in Rotterdam, and 1 m depth in general in the Netherlands.
Measurements confirm the significant influence of the ground coverage, mainly impacting the soil temperature in vertical (in-depth) direction. A detailed analysis reveals the quantitative effectiveness of the considered measures, indicating substantial cooling potential by modifying the ground coverage. Replacing concrete tiles with vegetation (in sandy soil) results in the most cooling effect of all analysed measures. White paint on concrete tiles emerges as particularly effective in reducing the soil temperature at the current depth in Rotterdam (0.7 m), and is considered an easily executable measure to prevent exceedances of the 25 °C threshold, mainly in case of urgency. In general, modifying the top layer as measure is considered feasible. This is because it avoids the need for excavation, in contrast to the alternative measures of relocation to a deeper level or in the shade. Additionally, the study quantifies soil temperature through simulations. A comparative analysis between simulations conducted by the soil temperature model and measurements facilitates an examination of the anticipated progression and the predicted effect of measures by the model, allowing for the formulation of recommendations to enhance the model.
As the results indicate that modifications to the ground coverage can significantly contribute to cooling the soil, this can mitigate potential threats to drinking water quality. The study advocates an integrated approach to decision-making, which includes collaboration between municipalities, drinking water companies, and research institutes. This cooperative effort is essential for identifying and implementing the most suitable and effective measures to safeguard high-quality drinking water, both now and in the future.