The effect of urban heat islands on geothermal potential: examples from Quaternary aquifers in Finland

The use of renewable energy can be enhanced by utilising groundwater reservoirs for heating and cooling purposes. The urbanisation effect on the peak heating and peak cooling capacity of groundwater in a cold groundwater region was investigated. Groundwater temperatures were measured and energy potentials calculated from three partly urbanised aquifers situated between the latitudes of 60° 25′N and 60° 59′N in Finland. The average groundwater temperature below the zone of seasonal temperature fluctuations was 3–4 °C higher in the city centres than in the rural areas. The study demonstrated that due to warmer groundwater, approximately 50–60 % more peak heating power could be utilized from populated areas compared with rural areas. In contrast, approximately 40–50 % less peak cooling power could be utilised. Urbanisation significantly increases the possibility of utilising local heat energy from groundwater within a wider region of naturally cold groundwater. Despite the warming in urban areas, groundwater still remains attractive as a source of cooling energy. More research is needed in order to determine the long-term energy capacity of groundwater, i.e. the design power, in urbanised areas of cold regions.