Geppert, Marielle; Hartmann, Kai; Kirchner, Ingo; Pfahl, Stephan; Struck, Ulrich; Riedel, Frank (2022). Precipitation Over Southern Africa: Moisture Sources and Isotopic Composition. JGR: Atmospheres,

Context of the Study

Southern Africa is characterized by arid and semi-arid landscapes and is particularly susceptible to extreme weather conditions. Intriguingly, over the last 100,000 years, extensive lakes have periodically formed in the central Kalahari desert, raising questions about historical changes in atmospheric circulation and precipitation patterns.

Geppert et al. conducted a study about the annual precipitation distributions throughout Southern Africa. They focused on the analysis of stable water isotope compositions, moisture transport pathways, and moisture sources.

Stable isotopes of hydrogen and oxygen (such as \(^{2}H\) and \(^{18}O\)) in water molecules vary slightly based on their source and the environmental conditions they have been through. By analyzing these isotopes, it is possible to trace the origins of water sources and to understand the pathways of moisture transport.

Changes in stable isotope ratios in precipitation can reveal shifts in atmospheric circulation patterns and climate. For instance, when water evaporates from the ocean, water molecules containing heavier isotopes of oxygen (\(^{18}O\)) and hydrogen (\(^{2}H\) or deuterium) are more likely to remain in the ocean. This results in a higher concentration of these heavier isotopes in the ocean, which is reflected in the \(\delta^{2}H\) and \(\delta^{18}O\) ratios of the ocean water. As the evaporated water forms precipitation and moves inland, separation continues and and further changes isotopic ratios occur. Analyzing these isotopic variations helps to reconstruct past precipitation regimes and thus provides insights into historical patterns of atmospheric circulation.

Data Collection

The study involved collecting water samples of precipitation and different surface waters in southern Africa between 2016 and 2021. The map shows the sampling locations and the sample type, which is: ocean, spring, lake, precipitation and river. Furthermore, the data of eight Global Network for Isotopes in Precipitation (GNIP) stations has been used.