Improving urban climate modeling within the Earth system model framework to support adaptation

Abstract

Alongside climate change and intensified human activities, urban areas are increasingly exposed to climate-related risks. Since CMIP5 in the 2010s, there has been a growing trend toward using Earth system models (ESMs) to investigate large-scale (i.e., global, regional, national) urban climate. This development challenges two traditional views: first, that urban areas occupy too small a fraction of the Earth’s surface to influence the global climate system within the ESM framework; and second, that ESMs are too coarse in spatial resolution (e.g., 1°, 2°) to resolve localized urban climate processes. This thesis aims to advance urban climate modeling within the ESM framework in response to the growing need for climate adaptation. We review previous studies that have developed urban climate modeling schemes for ESMs and applied ESMs to project urban climate, assess urban climate impact, and evaluate urban adaptation strategies. The literature review describes the global needs of urban climate adaptation and emerging large-scale urban climate simulations using ESMs. Despite progress in urban climate modeling within ESMs, applications of ESMs for supporting urban climate adaptation are inadequate due to model limitations and communication barriers. Model limitations include the implicit representation of urban surfaces and the parameterization of urban biogeophysical processes, as well as the lack of adaptation-oriented functionality. To address these challenges, this thesis proposes three complementary developments within the Community Earth System Model (CESM), a state-of-the-art ESM. First, instead of relying on the model's default three-class urban land-cover classification (i.e., tall-building district, high-density, and medium-density), we adopt the Local Climate Zone (LCZ) scheme as a more physically representative urban land-cover classification framework. Compared to the default model-dependent scheme, the LCZ scheme has been widely used in urban studies and helps bridge communication between the modeling community and a broader audience. We evaluated the performance of CESM—LCZ across 20 global urban flux tower sites. Second, we develop a traffic heat module to simulate traffic-related anthropogenic heat flux (AHF) in CESM, as it primarily accounts for emissions from a single sector—building energy usage. Based on tests at two sites, our approach to modeling traffic heat shows improved urban sensible heat flux. Third, we implement a transient urban albedo representation to emulate the climatic impacts of urban high albedo with specific implementation pathways. Although ESMs traditionally focus on natural processes, they rarely incorporate the effects of adaptation-oriented processes. Our new module of prescribing urban surface albedo at every time step explicitly accounts for the temporal evolution of such practices throughout the simulation.

Date of Award	23 Jun 2026
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Zhonghua Zheng (Main Supervisor), David Topping (Co Supervisor) & David Schultz (Co Supervisor)