Subsurface heat flow in an urban environment

Abstract

[1] The subsurface temperature field beneath Winnipeg, Canada, is significantly different from that of the surrounding rural areas. Downward heat flow to depths as great as 130 m has been noted in some areas beneath the city and groundwater temperatures in a regional aquifer have risen by as much as 5°C in some areas. Numerical simulation of heat transport supports the conjecture that these temperature changes can be largely attributed to heat loss from buildings and the temperature at any given point is sensitive to the distance from and the age of any buildings. The effect is most noticable when buildings are closely spaced, which is typical of urban areas. Temperature measurements in areas more than a few hundred meters away from any heated structure were only a few tenths of a degree Celsius greater than those observed outside the city, suggesting that other reasons for increases in subsurface temperature, such as changes in surface cover or climate change, may be responsible for some of the some of the observed increase in temperatures. These sources of additional heat to the subsurface make it difficult to resolve information on past climates from temperatures measured in boreholes and monitoring wells. In some areas, the temperature increases may also have an impact on geothermal energy resources. This impact might be in the form of an increase in heat pump efficiency or in the case of the Winnipeg area, a decrease in the efficiency of direct use of groundwater for cooling.

Urban heat island in the subsurface

“…The importance of landuse changes to subsurface temperature anomalies and the variability in the subsurface heat island will be addressed in this study through an examination of the subsurface heat island effect beneath Winnipeg, Manitoba. This has been previously documented by Ferguson and Woodbury [2004]. In the current study we present the results of a more recent temperature survey conducted in August 2007 and compare these results to previously measured temperatures.…”

“…Changes in snow cover can also have a noticeable effect on the thermal regime of the subsurface [Zhang, 2005]. Additionally, subsurface temperature measurements in urban areas have been found to approach 5 K above those observed in surrounding areas [Taniguchi et al, 1999;Ferguson and Woodbury, 2004;Reiter, 2006]. This change has been attributed to a combination of mesoscale climate, heat losses from buildings and land use changes, which are similar to the list of factors known to cause the urban heat island effect in SAT measurements.…”

“…Measurements were made in August 2002 [Ferguson and Woodbury, 2004] and 2007. Additional measurements were made in a subset of these wells in 2000.…”

“…[3] The urban heat island effect has been studied using subsurface temperatures in several studies [Taniguchi et al, 1999;Changnon, 2004;Ferguson and Woodbury, 2004;Taniguchi, 2006Taniguchi, , 2007. Taniguchi [2006] suggested a link between population density and the magnitude of the temperature perturbation in the subsurface in the Bangkok area.…”

Long-term climate change and surface versus underground temperature measurements in Paris

“…This correction is uncertain, as the near-surface temperature gradient can be affected by other causes, such as urbanization (e.g. Block et al, 2004;Ferguson and Woodbury, 2004) or groundwater flow (Smith and Chapman, 1983). Such effects should not affect our correction to first order.…”