From Paper to Proof: Revealing Congo Basin Warming Through Rescued Climate Archives

The Congo Basin in Central Africa remains one of the few regions globally where the Intergovernmental Panel on Climate Change (IPCC) has not reported observed trends in hot extremes or attributed such changes to anthropogenic influences, primarily due to the scarcity of in situ observational data. Similarly, observed changes in extreme daily precipitation since the 1950s have not been assessed for this region. Although extensive daily weather records exist, spanning from the 1900s to the early 2000s and covering numerous stations across the basin, the majority of these remain archived on paper, limiting their accessibility for climate analysis. Here, we present our historical weather data rescue project entailing archived data from 37 weather stations in the Democratic Republic of the Congo (DRC). We outline the digitization process of these archival records, comprising over 1 million individual observations, and describe the subsequent transcription using MeteoSaver version 1.1. From these records, we construct daily time series of daily maximum, minimum, and average temperatures, precipitation, as well as dry bulb and wet bulb temperatures measured at three times per day (06:00, 15:00, and 18:00). This newly transcribed dataset provides a critical foundation for undertaking hydroclimatic trend analysis in the Congo Basin, one of the world’s most data-scarce yet climatically significant regions. Using this data, we conduct an analysis of multi-decadal temperature trends across the basin. Our findings reveal a consistent and accelerating warming signal since the 1960s, characterized by a rightward shift in the distribution of daily maximum, minimum, and average temperatures with each successive decade. Median trends across the stations are 0.24°C, 0.09°C, and 0.18°C per decade for daily maximum, minimum, and average temperatures, respectively, corresponding to approximately 0.7°C, 0.3°C, and 0.6°C of warming over 30 years. We further find an increasing frequency of hot extremes and a decreasing frequency of cold events with each successive decade during the period 1960-1990, across the aggregated station data. Specifically, the most recent decade exhibits approximately twice as many hot days per year and about half as many cold days compared to the earliest decade. Overall, this analysis of newly digitized historical weather data for the DRC highlights the urgent need to close the knowledge gap on climate trends in the Congo Basin.