Global thermal spring distribution and relationship to endogenous and exogenous factors

In the last decades, the enormous potential for direct geothermal heat from aquifers attracted special attention, particularly toward those thermal springs indicating areas in which exploitation of geothermal energy might be economically feasible for indirect uses such as electrical power production. The availability of geochemical data besides the location of thermal spring areas assumes particular importance, especially in the first stages of a geothermal exploration program. In this work, we present a digitised format of the literature review of Gerald Ashley Waring on the geothermal springs of the world. This unprecedented dataset contains geographical coordinates (from georeferentiation) of ~6,000 geothermal spring areas, including complementary data such as temperatures, flow rates, total dissolved solids content (TDS, expressed in ppm), and quantitative chemical analysis of major elements (only for a few hundred sites). Using temperature and flow rate, we derive the heat discharged from 1483 thermal spring areas (between ~10^-5 and ~10³ MW, with a median value of ~0.5 MW and ~8300 MW in total). We complement this information with geological data sets currently available in the literature and analyse them using statistical and geospatial tools and a supervised machine-learning algorithm. We show that terrestrial heat flow, topography, volcanism, and extensional tectonic play a key role in the occurrence of thermal waters around the globe. These results can also be beneficial to address the geothermal interest towards specific and less studied areas and significantly drive the first steps of the geothermal surveys and detailed investigations. Finally, this data set in electronic format will be beneficial for future research on the spatial distribution of thermalism at a small scale and the variation of temperature and flow rate of several thermal springs in the last decades in certain regions.