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Climate Group

Urban Climate Research

The Urban Heat Island

The urban heat island (UHI) effect has been documented and researched for over a century (Howard 1833; Oke 1987). The UHI is a significant part of anthropogenic climate change studies (Karl et al. 1988) and its importance as a modifier of the urban environment has lead to ongoing measurement and modeling (Jauregui 1997; Hafner and Kidder 1999).

(http://eetd.lbl.gov/HeatIsland/HighTemps/UrbanProfile.gif)

There has been a simultaneous growth in the developed urban and suburban land area of Melbourne, which is expected to have increased the magnitude of the UHI and its spatial extent. The long-term urban warming component of UHI trends can be evaluated using differences between urban and rural climate stations. However, many cities, including Melbourne, do not have temperature records at a sufficiently fine spatial scale for mapping purposes. Instead, such spatial data are collected occasionally by direct field measurement or by inference from remotely sensed satellite data. It is important to understand the spatial details of local climate patterns and processes, because they combine complexly over time to determine the climate variability and trends measured at particular points. Therefore, the primary research goals of this study are (i) to quantify temporal urban warming trends in Melbourne over the last few decades, and (ii) to examine the spatial details of temperature over the Melbourne metropolitan area.

In addition to this scientifically important research, the project is also stimulated by the desire to integrate some real, if modest, research with undergraduate learning specifically as part of the Global change and the Earth system (ATS3558/ATM3261) subject. This innovate project reflects an international trend in science education (National Science Foundation 2001) and in the atmospheric sciences (Yarger et al. 2000). This project aims to provide a hands-on experience to include inquiry, the processes of science, and the excitement of research, which also develops communication and teamwork skills, critical thinking, and lifelong learning (National Science Foundation 2001). What were once separate research and teaching agendas are being combined into a common pursuit of learning. This view promotes the simultaneous and collaborative nature of learning about the world as a link between undergraduates, graduate students, and faculty members.

Urban Flux Network

Urban climates and the urban heat island are strongly driven by the nature of the urban surface. When vegetation and soils are replaced by buildings, roads and other impervious surfaces, this modifies the way the land surface and the atmosphere interact. Complex urban geometries and urban materials with high thermal admittance tend to increase the amount of energy stored in the urban fabric. Lots of hard, impervious surfaces limit infiltration in urban area and increase runoff, leading to decreases in evapotranspiration. These hard and dry impervious surfaces tend to support enhanced atmospheric heating. In combination with the slow release of stored heat during the night, commonly lead to warm urban environments and the generation of the Urban Heat Island.

To better understand these land-surface / atmosphere interactions in urban environments across the globe, a number of urban 'flux towers' have been established to directly observe the urban surface energy balance. The International Association for Urban Climate (IAUC) has co-ordinated the Urban Flux Network with the goal to network research groups and activities in the international urban flux community. Currently the database hosts over 30 towers from 5 continents.

The Urban Flux Network can be found here.

Contributing to this network, an urban flux tower was operated by Monash University in the residential suburb of Preston, Melbourne, Australia from August 2003 - June 2005. Results showed that evapotranspiration rates at the site were very low due to limited water availability from a combination of drought, rapid stormwater runoff and restricted irrigation. Urban heat storage (influenced by urban morphology and surface albedo) and atmospheric heating dominated - which supports the development of the urban heat island.

Funding is being sought to re-establish Preston as an ongoing flux tower site.

Thermal benefits of street trees

Monash University and the City of Melbourne are conducting a joint research project investigating the thermal effects of street trees. Further information can be found here.