Essays on Urban Climate Model Evaluation and Application

The field of urban climatology as a subfield of atmospheric science / physical geography has developed significantly over the past 3 decades. Major advances have occurred in the theoretical understanding of the urban effect at multiple spatial and temporal scales, as well as in empirical work seeking to observe and ultimately predict urban scale phenomenon. It is this latter development, particularly in respect to urban heat and moisture, that forms the basis of this work. Less than 5 years ago, the concept of partitioning the urban area into distinct geographic units based on the potential thermal modification of the near surface climate was proposed within the field to bring greater rigor, clarity and transferability to observations made within urban areas. The Local Climate Zone (LCZ) approach has since been applied in multiple cities globally, which has demonstrated its efficacy in understanding the urban heat island (UHI) effect through observations and transferring those results across multiple cities. However as with global scale temperature anomalies, the UHI can be viewed as symptomatic of the underlying processes rather than purely as a response i.e. while we now are capable of observing enhanced air temperatures around cities, addressing the issue requires a deeper understanding of the processes that give rise to this phenomenon, particularly if solutions are to be transferred into urban planning practices and environmental policies. To that end, urban climate models are an invaluable tool for examining urban processes in more detail. However, their application in urban areas (particularly for planning problems) remains ad hoc and unsystematic. In fact, many cities in the economically developing world lack even basic data describing (i) the underlying city, its sealed surface extent, vegetation, building materials and so forth and/or (ii) knowledge of the overlying atmosphere in and around the city, required to apply such models. In this collection of papers, a formal modelling and evaluation approach is proposed, elaborated on and applied which utilises the LCZ system. While LCZs were designed strictly for observations of the air temperature at 2m, due to its generality and resulting uptake within the urban climate community, it is argued to be an effective approach for modelling, particularly in data poor settings. The LCZ approach is linked with the Surface Urban Energy and Water Balance Scheme (SUEWS) model, a mid-complex urban energy and water balance model. Hence, the approach is referred to as the LCZ-SUEWS approach. The application of the approach primarily focuses on Dublin city (Ireland). This was done as the city houses three (2 ongoing and 1 retired) eddy-covariance flux towers used to evaluate the approach, however the results are intended to be transferrable to other domains. Three primary conclusions can be drawn from this body of work. Firstly, the LCZ-SUEWS approach performs equally well in data poor, data rich settings, meaning the approach can be applied anywhere to provide an initial assessment of the urban energy balance. Secondly, the adoption of the approach yields the additional benefit of improving communication with the urban planning community in terms of illustrating the processes that give rise to the urban effect e.g. lack of photosynthecially active vegetation, standing water bodies, and high proportion of built up coverage. This allows for more geographically and physically targeted design interventions to reduce the negative impacts of urban development such as excess heat and lack of moisture. Thirdly, there is a need for an agreed framework on model evaluation which emphasises external independent evaluation and employs novel sources of observational data, for example, remote sensing. This would improve the trustworthiness of urban climate models and further encourage their uptake