University of the Witwatersrand: Tracking rainfall moisture in Lesotho

Researchers from Wits University and the University College in London (UCL) recently undertook a field trip to the mountainous kingdom, Lesotho, as part of the quest to explore the source of moisture that influences rainfall in Lesotho. The team of climatologists and water experts set off on 2 June headed for the Caledonspoort Border Post leading into Lesotho. By lunch time, the team had crossed into the country and immediately set about collecting water samples.
Associate Professor of Physical Geography in the School of Geography, Archaeology and Environmental Studies at Wits, Jennifer Fitchett says studies into rainfall moisture around Lesotho are critical for several reasons.

“First, Lesotho is considered the water tower of southern Africa, hosting the Lesotho Highlands Water Project, which supplies South Africa with water. Understanding the dynamics of moisture sources for Lesotho is important in understanding the water security for the region,” says Fitchett.

Another reason says Fitchett is that the Lesotho Highlands receive approximately eight snowfall events per year, and thus “provides us with the best opportunity to explore the isotopes of snow relative to that of groundwater and rivers. If there is a difference in the moisture sources for winter and summer precipitation, this would be most likely to be traced in this environment.”

The research also helps to understand rainfall and droughts in South Africa and the movement of moisture that has evaporated from the Indian Ocean to the two neighbouring countries – South Africa and Lesotho.

This study is one of several joint research projects under the Wits-UCL Strategic Partnership Seed Funding launched in 2019. Research awards are granted annually and carry up to approximately R100 000 (£5,000), per project. Thus far, 18 research projects in different disciplines have received funding. The peer-to-peer collaboration promotes research excellence and interaction with a range of students and early career researchers.

Fitchett is working with Principal Investigator Emeritus Professor Anson Mackay and his colleague Professor Jonathan Holmes (UCL). Mackay, however, was not able to join the field trip due to health reasons, but in his place Dr Simoné Dahms-Verster (Wits) and Prof Chris Curtis (UJ) joined Fitchett and Holmes for the fieldwork. The team covered massive ground during the four-day trip moving from Caledonspoort to Sani Top, Sani Top to Katse Dam, Katse Dam to Mafeteng, and Mafeteng to Maseru collecting samples from snowpacks, rivers, dams and springs across the northern half of Lesotho.

“In addition to collecting water samples for analysis, we also collected the GPS coordinates and altitude using a Garmin GPS, the air temperature using a Kestrel 5000, and the water temperature, dissolved oxygen, electrical conductivity and pH using a YSI. We collected a total of 35 samples,” says Fitchett.

The water samples are currently being analysed at the Bloomsbury Environmental Isotope Facility at UCL.

Pioneering own solutions

Research equipment can be costly, hard to source and sometimes there is a mismatch between the product on the market and the research needs. The climate and environmental group faced this challenge when it came to rainwater collectors. To overcome this, Holmes built and tested a rainwater collector in his home in the UK and it also proved to be effective in preventing evaporation (a critical factor for rainwater isotope analyses). This prototype was replicated in Johannesburg by Holmes and Fitchett during Holmes’ visit to Wits in June 2022, with the assistance of the Civil and Environmental Engineering laboratories at Wits. Preliminary tests confirmed effectiveness and the equipment has been deployed at three locations.

The purpose is to obtain weekly rainwater samples from across South Africa against which the oxygen and hydrogen isotope ratios from the water samples in Lesotho can be compared. This will help the team in further understanding the variation in water isotope signatures across southern Africa, and to link these to the primary moisture sources.