An overview of observed changes in precipitation totals and extremes over global land, with a focus on Africa

Precipitation is one of the crucial climatic variables that has significant impact on the natural and human systems, with several important sectors of the Earth's system responding to its spatiotemporal variability. Consequently, various studies are conducted on global and regional scales to evaluate changes and trends in precipitation, with more emphasis on extremes. This review assesses existing studies on precipitation trends conducted using in situ data or gauge-based datasets, examining their comparability and consistency to identify regional trends. It also seeks to demonstrate the pressing challenges related to the availability and accessibility of precipitation data, with a particular focus on Africa. The existing gauge-based global and regional studies are limited and generally diverse, making it difficult to infer robust regional trends from their findings. Complex differences are observed in data periods, analysis region, methods, precipitation metrics, and the type of datasets used. This review notes that there is uneven station distribution in each continent, and that this is also mirrored in the existing global datasets, while Africa constitutes one of the least covered global regions. Yet, a few studies agree that long-term precipitation totals exhibit non-significant decreasing trends over northern Africa and significantly decreasing trends in parts of western Africa. Conversely, long-term annual precipitation totals have increased significantly over Asia, northern and central Europe, southern Canada and the eastern United States. Generally, despite accounting for different analysis periods, total and extreme trends match up for most global regions. Areas with significant increasing extreme trends, such as RX1day, RX5day and R95pTOT indices, include South Africa, eastern Asia, Canada, northern and central Europe, northeastern United States, and western Australia. Overall, more efforts are needed to significantly expand station coverage across Africa and ease restrictions to allow greater access to data. Initiatives to establish and monitor climate stations across Africa need to be supported. Regional studies that use in situ or gauge-based datasets need to increase and employ comparable analysis regions and data periods, as well as assess and adjust for systematic biases in precipitation data at urban stations.