Water temperature aspects of a (geo)thermal stream in context of climate change adaptation

Climate change adaptation in urban areas often involves the expansion and further development of blue-green infrastructure. In cities where stream systems are routed in the underground, there is potential to adapt public spaces to the growing requirements caused by climate change by daylighting  these streams. Usually, urban streams are used as climate change adaptation in terms of PET (physically equivalent temperature) reductions. Beside their usage in cooling public spaces, streams, especially spring-fed streams, also provide potential for thermal utilization as a climate change adaptation measure in the built environment. In case streams originating from thermal springs temperature patterns are inverted. Showing the highest temperatures at the spring and cooling down on their way downstream. Climate change adaptation initiatives include efforts to utilize their thermal potential for geothermal energy. One example is MaDoKli Project, focusing on Mannersdorfergraben in Eastern Austria. The region is characterized through a focus on agriculture and open fields next to the city of Mannersdorf. The initial conditions of the project area show an interesting situation with a constant discharge in a range of 14 – 27 l/s measured with 23° C year-round at the spring. Therefore, the warm stream is intended to be integrated into the municipality’s energy system through heat exchange for thermal energy extraction. The Mannersdorfergraben is monitored over its 6 km long flow path. Water temperature is measured at 300 m intervals using HOBO Bluetooth Onset 1-800-loggers, covering the springs, the flow path in the underground and the open channel. The inverse temperature regime was investigated over a six-month period in 2025 at 15-min interval. The measurements are intended to support a sensitivity analysis assessing how fluctuations of +/- 5° C impact the total water temperature regime of the stream. The data allows the identification of the longitudinal extent affected by thermal stress, manifested as river temperature reduction in heating period and thermal pollution during the summer period. Early results indicate that approximately halfway along the open flow section, the effect of thermal energy extraction diminishes and the water temperature returns to its initial baseline.
Additionally, the results are intended to help determine the impact of the thermal intervention in the flow system on the stream and its ecosystem.