Climate change and subsurface urban heat island: ground surface, well temperature and surface air temperatures correlation in the city of Padova, Italy

The geothermal heat available in urban environments is becoming increasingly interesting for its possible use as geothermal resource available at shallow depth beneath cities.

This heat is mainly composed of the natural thermal background regime of the area of interest, the anthropogenic effect due to the urbanization process and the contribution due to the global warming. To be able to differentiate between these contributions provides a better understanding on how the urban heat resource could be used and managed.

In detail, global climate warming has a direct consequence in the increase of surface air temperature over time affecting, at local scale, the heat energy exchanges between the air-ground interface. The air temperature fluctuations can penetrate several meters deep into the subsurface raising the ground surface temperatures and, consequently, the mean annual temperature of shallow aquifers. A detailed analysis of temporal series of air, ground and shallow depth ground temperature data is expected to show this behaviour.

The city of Padova and its surroundings, located in the north-east of Italy, were selected as case study area. Here, starting from a comprehensive analysis of surface air temperature variation in the last 60 years, the local climate change was tracked. The correspondence between increase temperature on surface and underground was researched using at first underground temperature profile data collected in surface groundwater wells in urban and agricultural areas. The preliminary results confirm the influence of air temperature variation, affected by global warming, on shallow depth ground. Next step consists in the analysis of underground temperature profile variations over approximately 100 m depth in a geothermal borehole installed in the city centre, to assess the contribution of the climatic temperature to the background thermal regime and anthropogenic heat effect.