Abstract
Urban areas are major contributors to the alteration of the local atmospheric and groundwater environment. The impact of such changes on the groundwater thermal regime is documented worldwide by elevated groundwater temperature in city centers with respect to the surrounding rural areas. This study investigates the subsurface urban heat island (SUHI) in the aquifers beneath the Milan city area in northern Italy, and assesses the natural and anthropogenic controls on groundwater temperatures within the urban area by analyzing groundwater head and temperature records acquired in the 2016–2020 period. This analysis demonstrates the occurrence of a SUHI with up to 3 °C intensity and reveals a correlation between the density of building/subsurface infrastructures and the mean annual groundwater temperature. Vertical heat fluxes to the aquifer are strongly related to the depth of the groundwater and the density of surface structures and infrastructures. The heat accumulation in the subsurface is reflected by a constant groundwater warming trend between +0.1 and + 0.4 °C/year that leads to a gain of 25 MJ/m2 of thermal energy per year in the shallow aquifer inside the SUHI area. Future monitoring of groundwater temperatures, combined with numerical modeling of coupled groundwater flow and heat transport, will be essential to reveal what this trend is controlled by and to make predictions on the lateral and vertical extent of the groundwater SUHI in the study area.
Highlights
Urbanized areas rely on abundant and uncontaminated groundwater resources to withdraw drinking water and, more recently, the urban subsurface has been used to extract low enthalpy geothermal energy
It has been demonstrated that the development of the subsurface urban heat island (SUHI) is related to anthropogenic modifications of the land use and the percentage of area covered by buildings (Benz et al 2015, 2018)
This study reveals the extent and the intensity of the urban heat island effect in the groundwater beneath the Milan city area and attempts to identify the natural and anthropogenic controls on the thermal regime
Summary
Urbanized areas rely on abundant and uncontaminated groundwater resources to withdraw drinking water and, more recently, the urban subsurface has been used to extract low enthalpy geothermal energy. The UHI is referred to as the air/ground/groundwater positive temperature anomaly encountered in the urban environment with respect to the surrounding rural areas. The UHI is often documented in densely populated and highly developed cities as its formation is related to the modifications of the environment due to urbanization such as land artificial covering/sealing with buildings, asphalt and surface infrastructures, and heat losses from anthropogenic sources. Such factors modify the solar radiation balance and the energy balance at the earth’s surface, leading to the local warming of the air and the ground temperature. Benz et al (2015) evaluated the thermal contribution of various anthropogenic heat sources for two European cities revealing the building basements and the elevated ground surface temperatures as the dominant heat sources on a citywide scale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
