Groundwater temperature study - Subsurface Urban Heat Island in the city of Wrocław (Poland)

The average air temperature in the world has increased recently. Over the past 20 years, the global average has increased by 0.6 C and continues to increase [1]. In south-western Poland, in Wrocław, for the same period, the recorded increase in the average air temperature is approx. 0.5 °C [2]. The reason for this phenomenon is human activity. The process of urbanisation has created another phenomenon called the Urban Heat Island (UHI), which can be studied analysing for example the Land Surface Temperature (LST). The combined effect of the UHI and climate change can influence groundwater temperature by penetrating underground. The phenomenon of elevated groundwater temperatures is called the Subsurface Urban Heat Island (SUHI) [3,4]. While the Urban Heat Island effects is generally negative and widely investigated, the higher groundwater temperature may have positive aspect, such as e.g. use in heat pumps. The SUHI phenomenon is less understood than the UHI one.
This presentation focuses on the spatial distribution of temperature in shallow aquifers in the city of Wroclaw (SW Poland) developed with various interpolation techniques and based on measurements made in a network of piezometers in the 2004-2005 period. In total 67 locations have been measured and the temperatures recorded varied between 1.1 °C and 24.5 °C with the average of 13.2 °C. The data has been processed with the IDW, spline and kriging interpolation methods. The groundwater temperature distribution was analysed spatially, taking into account the then land use and location of technical infrastructure. In addition, an attempt has been made to compare the distribution of groundwater temperature with the Land Surface Temperature. The latter was determined based on Landsat 5 satellite imagery.
The interpolated groundwater temperature maps have made it possible to analyse and present graphically the spatial distribution of temperature and link it to the LST UHI for the analysed period.

Bibliography:

[1] Global Climate Change https://climate.nasa.gov/ (accessed on 11 January 2022)

[2] Polish climate 2020. Institute of Meteorology and Water Management, National Research Institute. Available online: https://www.imgw.pl/sites/default/files/2021-04/imgw-pib-klimat-polski-2020-opracowanie-final-pojedyncze-min.pdf. (accessed on 11 January 2022)

[3] Luo Z., Asproudi C., Subsurface urban heat island and its effects on horizontal ground-source heat pump potential under climate change, Applied Thermal Engineering, Volume 90, 2015, doi: 10.1016/j.applthermaleng.2015.07.025.

[4] Zhu, K., Bayer, P., Grathwohl, P., and Blum, P. (2015), Groundwater temperature evolution in the subsurface urban heat island of Cologne, Germany, Hydrol. Process., 29, 965– 978, doi: 10.1002/hyp.10209