Another groundwater paper I enjoyed: Global patterns of shallow groundwater temperatures by Susanne A Benz, Peter Bayer and Philipp Blum, , ,
Click here for supplementary materials.
Brings back memories of shallow temperature surveys we conducted in Dixie Valley, NV, in the late 1970s - early 1980s as part of a Department of Energy-funded geothermal exploration project. Obviously a global scale was something we could only dream about in those days.
I also recall a 1971 PhD dissertation by Donald J. Supkow, Subsurface Heat Flow as a Means for Determining Aquifer Characteristics in the Tucson basin, Pima County, Arizona. Don was finishing his doctoral work as I was arriving and was a student of my advisor, Gene Simpson. He was an 'older' (late 30s?) student. He took pains to explain what he had done, and the 'light' that went off when he realized that he did not have to measure groundwater temperatures directly. I now wish I had been more mathematically sophisticated at the time because Don was talking about solving the conductive-convective heat transport equations and I could barely follow him. Something about a 'valley mapping function'. I do know he successfully used the approach in his consulting work. Perhaps I will fetch his dissertation and give it a read one of these days.
Only meters below our feet, shallow aquifers serve as sustainable energy source and provide freshwater storage and ecological habitats. All of these aspects are crucially impacted by the thermal regime of the subsurface. Due to the limited accessibility of aquifers however, temperature measurements are scarce. Most commonly, shallow groundwater temperatures are approximated by adding an offset to annual mean surface air temperatures. Yet, the value of this offset is not well defined, often arbitrarily set, and rarely validated. Here, we propose the usage of satellite-derived land surface temperatures instead of surface air temperatures. 2 548 measurement points in 29 countries are compiled, revealing characteristic trends in the offset between shallow groundwater temperatures and land surface temperatures. Here it is shown that evapotranspiration and snow cover impact on this offset globally, through latent heat flow and insulation. Considering these two processes only, global shallow groundwater temperatures are estimated in a resolution of approximately 1 km 1 km. When comparing these estimated groundwater temperatures with measured ones a coefficient of determination of 0.95 and a root mean square error of 1.4 K is found.
Wonder whatever happened to Don?