Urbanization's role in shaping temperature records: Insights from İzmir, Türkiye

Abstract

The urban heat island concept was introduced to literature around the early 80s when the construction of urban areas started to increase due to the increasing population of cities. The term urban heat island is defined as the temperature difference between urban and rural areas. From the early 80s until today, numerous studies have been conducted to deeply understand how the urban atmosphere interacts with its surroundings and how urban heat islands affect meteorological phenomena. Numerical weather prediction (NWP) models like The Weather Research and Forecasting (WRF) come in handy to simulate these phenomena. The WRF model is a sophisticated numerical weather prediction tool designed to serve atmospheric research and operational forecasting needs. As an NWP model, WRF utilizes mathematical equations representing atmospheric physics and dynamics to simulate weather patterns based on current observational data. Its versatility and modular structure allow for various applications, from short-term weather predictions to long-term climate studies. WRF stands out due to its high spatial and temporal resolution, which enables detailed simulations of meteorological phenomena at local, regional, and global scales. This model supports advanced data assimilation techniques and can integrate diverse data sources, enhancing its predictive accuracy. By providing detailed, reliable forecasts, WRF and other NWP models play a crucial role in weather-related decision-making, disaster preparedness, and environmental management, ultimately helping to safeguard lives and property. WRF model has significantly advanced the study of urban heat islands (UHIs) by providing high-resolution simulations of atmospheric conditions over urban areas. This numerical prediction model allows researchers to analyze the intricate interactions between urban landscapes and meteorological phenomena such as heat waves and allows scientists to study the characteristics and impacts of UHIs more accurately. In this study it was aimed to understand how urban heat island effect behavior of atmosphefric dynamics under heat wave conditions for 3rd most populous city of Turkiye, İzmir. Due to the mentioned advantages, it was decided to conduct the study using WRF model version 4.3. After preparing the necessary infrastructure and setting up the model, it was started to search the parameter set would work with. Based on the results of our previous studies within the same domain, the parameterization set best represents the region selected. One of the most critical aspects of the study was to run the model with land use information that accurately represents urbanization. Therefore, instead of using the default land use data, Coordination of Information on the Environment (CORINE) data was used as the base for the model, thus laying the foundation for our study. We forced the model with ECMWF reanalysis data while running it and determined the case date using observational data provided by the Meteorological Directorate General. After selecting the date, we ran the model for July 2023, including the record-breaking day. Then, the outputs were compared with station observations to see how closely the model's results matched actual data, and the effectiveness and accuracy of the model were assessed. After determining the model's performance, the performance of the parameterization set once again was validated. Then, the model ran again with the same settings, replacing the urban land use category in the CORINE data with the nearest rural area category. We analyzed the contributions of the interaction between the city and the atmosphere to the temperature on the record-breaking heat day by considering atmospheric boundary layer heights, temperature profiles, and atmospheric forces such as buoyancy. The study revealed that replacing urban areas with rural land use significantly altered the temperature of the area throughout the entire month. Notably, the minimum temperature difference between urban and rural areas during the record-breaking heat day occurred at night, consistent with the urban heat island effect. Additionally, there was a noticeable difference in boundary layer height when comparing urban and non-urban runs. During the record-breaking day, the buoyancy flux was higher for the urban run, while it was lower at night. This variation in buoyancy flux requires further investigation to fully understand the underlying mechanisms.