Heat transport from atmosphere through the subsurface to drinking‐water supply pipes

Drinking‐water quality in supply pipe networks can be negatively affected by high temperatures during hot summer months due to detrimental bacteria encountering ideal conditions for growth. Thus, water suppliers are interested in estimating the temperature in their distribution networks. We investigate both experimentally and by numerical simulation the heat and water transport from ground surface into the subsurface, (i.e., above drinking‐water pipes). We consider the meteorological forcing functions by a sophisticated approach to model the boundary conditions for the heat balance at the soil–atmosphere interface. From August to December 2020, soil temperatures and soil moisture were measured dependent on soil type, land‐use cover, and weather data at a pilot site, constructed specifically for this purpose at the University of Stuttgart with polyethylene and cast‐iron pipes installed under typical in situ conditions. We included this interface condition at the atmosphere–subsurface boundary into an integrated non‐isothermal, variably saturated (Richards') the numerical simulator DuMux 3. This allowed, after calibration, to match measured soil temperatures with ±2°C accuracy. The land‐use cover influenced the soil temperature in 1.5 m more than the soil material used for back‐filling the trench above the pipe. Core Ideas We measure and model the temperature of groundwater recharge. We solve the heat and water balance at the atmosphere–subsurface interface. Data: time series of hydrometeorological parameters, hydraulic, and thermal material properties. Goal: estimate temperatures relevant for buried drinking‐water supply pipes. Core Ideas We measure and model the temperature of groundwater recharge. We solve the heat and water balance at the atmosphere–subsurface interface. Data: time series of hydrometeorological parameters, hydraulic, and thermal material properties. Goal: estimate temperatures relevant for buried drinking‐water supply pipes.