Study of groundwater temperature spatio-temporal variation in the city of Wroclaw. Preliminary results.

Abstract

In Wrocław over the past 20 years, the recorded increase in the average ambient air temperature is approx. 0.5 °C. In addition, urbanisation has created a phenomenon called the Urban Heat Island (UHI). The combined effect of the UHI and climate change can influence groundwater temperature by penetrating underground. The phenomenon of elevated groundwater temperatures in urban areas is called the Subsurface Urban Heat Island (SSUHI). This study focuses on the spatial distribution of temperature in shallow aquifers in the city of Wroclaw. The spatial distribution was analysed based on groundwater temperature maps developed with various interpolation techniques. The results of measurements in a network of 65 piezometers conducted in the 2004-2005 hydrological year have been used in this study. The temperatures recorded show seasonal variation with the lowest recorded in February (1.3 °C) and the highest in August (24.5 °C) with the annual average of 13.2 °C. The data has been processed with the Inverse Distance Weighted (IDW), Radial Basis Function (RBF) and Kriging interpolation methods. Furthermore, the cokriging method based on multivariate linear regression models has been used to assess if variable such as distance from the city centre improve the interpolation performance expressed as the lowest RMS error value. It has been established that the Kriging univariate regression model based interpolation method produced the best results (RMS error equal to 1.33 °C) and that the distance from the city centre has improved the accuracy of interpolation.