2.1. Precipitation
The Global Precipitation Climatology Centre (GPCC, Schneider et al., 2014; Becker et al., 2013) was used to assess the spatial and temporal patterns of rainfall over the Congo basin. The data provides reliable monthly gridded data sets of global land-surface precipitation at 0.5 x 0.5 , covers the period from 1901 to 2014, and can be downloaded from the GPCC data portal (www.ftp.dwd.de/pub/data/gpcc/html/downloadgate.html). The updated CRU precipitation data (Harris et al., 2014) was also used in this study. This version of the data (CRU TS3.10) includes the number of stations used in the interpolation, thus allowing an objective determination of the reliability of values. Apparently, the two datasets go back as far as 1901 and we acknowledge the limitations of GPCC gauge distribution over the Congo basin, which may not be as dense as other tropical regions. However, the GPCC has more gauge locations than CRU over the region. Given that this study is over the entire Congo basin region (about 3.7 million km2), the spatial resolution of 0.5 is suitable in resolving the sources of variability in the Congo region. Also, the error variance in GPCC and CRU is significantly less compared to satellite products (Ndehedehe et al., 2019). We used the GPCC data in all our analysis because of its reliability and as it is the most commonly used product with more ground observations from stations worldwide in the validation of global precipitation data sets. But a key limitation of the CRU data as highlighted by its data providers is uncertainties and unreliability in estimated trends. Overall, the uncertainties and ambiguities surrounding the Congo precipitation is still an ongoing discussion and it is open to further conversation in future studies.