The researchers of the Institute for Geological and Geochemical Research at the Research Centre for Astronomy and Earth Sciences (ELKH CSFK FGI) have created a database of amount-weighted annual mean precipitation tritium activity isoscapes for the Adriatic-Pannonian region covering the second half of the 20th century and the first decades of the 21st century, a period that has not been represented by the available global models to date.

Tritium is a radioactive isotope of hydrogen with a half-life of 12.32 years. Tritium is introduced into the hydrological cycle following oxidation. Due to its relatively short half-life, it is ideal for studying processes (such as the mixing and the flow of waters) that occur on a time scale of fewer than 100 years. However, a crucial prerequisite for its application is to know the spatial and temporal changes of tritium activity in precipitation, something which is not readily available on a global scale. As a result, currently the application of tritium activity of water samples in hydrological sciences can only be achieved with great compromises.

In a Slovenian-Hungarian bilateral research project, researchers have collected more than 8,000 pieces of data on tritium activity of monthly precipitation from more than 40 precipitation monitoring stations across the studied region, representing a temporal coverage of approximately 60 years (1961-2017). After investigating the temporal and spatial characteristics of the compiled dataset and identifying and removing the outliers, it was possible to derive the final findings of the project, annually interpolated tritium isocapes for the Adriatic-Pannonian region (called the AP3H_v1 database) for the period of 1976-2017 were derived.

The details are presented in an article published in the journal Earth System Science Data under the title “Isoscape of amount-weighted annual mean precipitation tritium (3H) activity from 1976 to 2017 for the Adriatic–Pannonian region – AP3H_v1 database” by authors Z. Kern, D. Erdélyi, P. Vreča, I. Krajcar Bronić, I. Fórizs, T. Kanduč, M. Štrok, L. Palcsu, M. Süveges, G. Czuppon, B. Kohán and I. Gábor Hatvani. The 1×1 km grid resolution database is available for download in an open access format.

The AP3H_v1 database provides great opportunity for the hydrological modeling community to use site-specific or watershed specific interpolated values instead of using remote station data or ad hoc composite curves. This means that these isoscapes serve as a reference dataset for studies on infiltration dynamics, water transport through various compartments of the hydrological cycle, mixing processes and run-off modeling, for example, to estimate mean residence time in surface waters and groundwater.

The video supplement of the article prepared by D. Erdélyi et al. shows in annual increments how the mean tritium activity in precipitation changed between 1976 and 2017. It clearly mirrors the well-known decadal decline in precipitation tritium activity indicating the depletion of radioactive hydrogen released to the atmosphere during the thermonuclear tests in the 1960s. It should also be noted that besides this overall temporal trend, clear sub-regional spatial patterns can also be observed.