Rescued weather records reveal hot days became nearly twice as common in the Congo Basin over two decades

New research led by Vrije Universiteit Brussel (VUB) and published in the journal Earth System Dynamics shows a clear warming signal across the Congo Basin since the 1960s, using historical weather records from the Democratic Republic of the Congo (DRC). These records come from the paper archives of the Institut National pour l’Etude et la Recherche Agronomiques (INERA) in Yangambi, DRC, and the State Archives of Belgium.

Rescuing a million weather observations

During two field campaigns in 2023, Derrick Muheki, a researcher at VUB and lead author of the study, collaborated with INERA staff and Ghent University (UGent) to photograph more than 9,000 handwritten monthly sheets of weather observations recorded at 37 stations across the DRC.

Using MeteoSaver, open-source software developed by Muheki at VUB in collaboration with the team at the UGent Centre for Digital Humanities, the research team automatically transcribed these observations into digital spreadsheets. They used these to understand changes in temperature and rainfall across the Congo Basin.

The resulting database contains more than 1 million daily (and sometimes subdaily) weather observations that, together with previously rescued data, represent one of the largest climate data sets for the Congo Basin region, which had until now been overlooked by the research community.

Hot days nearly doubled

By analyzing this new database, the authors document for the first time changes in hot extremes in the Congo Basin since the 1960s:

• Daily maximum, minimum and average temperatures rose by tenths of a degree per decade during 1961–1990. During that period, maximum temperatures warmed by about 0.7°C, minimum temperatures warmed by 0.3°C and average temperatures warmed by 0.5°C.
• Data from weather stations with longer records show that this warming of the Congo Basin continues into the 2000s.
• Each successive decade shows an increase in the number of hot days per year, with hot days getting hotter, while the number of cold days decreases, consistent with trends around the world. On average, the number of hot days per year nearly doubled between the 1960s and the 1980s, confirming the unequivocal warming trend in the region.

Examining past rainfall from three weather stations, the authors also observe that the number of heavy rainfall events at two of these stations doubled in the 1980s compared with the 1960s. This observed increase in the frequency and intensity of extreme weather events in the DRC is consistent with trends around the world, linked to increasing global temperatures driven by continued fossil fuel emissions.

Fragile archives fill critical climate gaps

Historical climate data for Central Africa have until now been extremely sparse, and this open-access database contributes new observational evidence to establish the climate context for a region that is strongly affected by climate change today. It also provides important information to evaluate and improve climate models in the region and underscores the importance of data rescue efforts around the world.

Muheki, lead author of the study and a doctoral researcher at VUB, said, “Seeing how fragile these paper archives were as I was visiting INERA made me realize how urgent this data rescue work is. Just months before my visit, part of the archive had been damaged by fire.

“We could have lost decades of irreplaceable data. Accessing more of these records will help us improve reconstructions of our climate history or improve our projections of future climate change in this part of the world, where adaptation to climate impacts is already a necessity.”

Wim Thiery, senior author of the study and a professor at VUB, said, “Our research provides new observational evidence of climate change in this data-sparse yet climatically significant region. This is particularly important because Central Africa remains one of the few regions where the last Intergovernmental Panel on Climate Change (IPCC) report could not confirm an increase in hot extremes, largely due to the lack of past observations and scientific studies.

“Our work further highlights the urgent need for more data rescue projects, especially in data-sparse regions, to close knowledge gaps on climate trends. This is particularly important for regions in the Global South that are already severely affected by climate change today.

“These regions are least responsible for climate change, yet suffer the brunt of the impacts, and these new observations will help inform decision-making when it comes to adaptation and a just transition.”

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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