Congo Basin Hydrology, Climate, and Biogeochemistry. Группа авторов

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Figure 5.1 Spatiotemporal SPEI patterns of the Congo basin using 12‐month gridded SPEI values (a–f). Localized spatial SPEI patterns (right) correspond to the temporal evolutions (left) and actual SPEI values to be used for drought classification (drought threshold is in red) are jointly derived from the spatial and temporal patterns. The SPEI time series (blue) are filtered to cushion the effect of residual short‐term seasonal signals and also for better representation.

Moreover, there are few drought episodes in the southwestern region of the basin (Figure 5.1c,d). The evolution of wet episodes in the southwestern region suggests it appears to be wet most of the times (Figure 5.1c,d). However, since 2010, the temporal patterns of SPEI in the southwestern region have been largely somewhat less than moderate (Figure 5.1c,d). The decomposition of SPEI over the basin also shows that drought conditions of the early 1980s affected the northern section in the Central Africa Republic (CAR) (Figure 5.1e,f). The frequent episodes of droughts in CAR obviously are in sharp contrast to the wet episodes observed in the southeast region of the basin (SPEI‐3, Figure 5.1). Some moderately wet periods between 1995 and 2002 (Figure 5.1e,f) are also noted in the CAR region. The latter is a humid tropical wet and dry savannah ecosystem largely characterized by considerable changes in annual and seasonal rainfall that is in opposite phase with the southern section. Arguably, the nourishment of the Congo basin hydrology and freshwater ecosystems also emanates from the southern end of the basin where extreme droughts tend to be more frequent (Figure 5.1a,b). As this region is also characterized by high rainfall amounts, which occur all through the year except during the June–August period, a shift in hydrological regime of the Congo Basin is more likely. Drought intensities over the Congo basin are conspicuously moderate or probably less. Droughts persisted between 1992 and 2001 with more than 40% coverage between 1994/1995 and early 2006 (Figure 5.2a,b). The observed extreme drought between 2004 and 2006, one of the post‐2000 period with widely acknowledged hydrological drought period in the basin reported in the literature also persisted, fluctuating between 25% in 2004 and more than 40% in 2006 (Figure 5.2b). During the last few decades (between 1984 and 2011), recurring severe and extreme drought episodes have affected on the average at least 30% of the Congo Basin (Figure 5.2). While the 1994 extreme droughts reached 50%, in other periods (e.g., 1992, 1999, 2004, 2005/2006), only about 30% of the basin on average has been affected by extreme drought during the 1991–2011 period (Figure 5.2a,b). This increasing intensity in extreme drought episodes is consistent with the results indicated in Figure 5.1. However, between 2012 and 2016, drought episodes and their intensities have diminished over the Congo Basin (Figure 5.2), consistent with the temporal SPEI patterns shown in Figure 5.1. But the intensity of the well‐known large‐scale extreme droughts of the 1980s, which affected Africa, are less and not as widespread in the Congo Basin compared to other African sub‐regions where drought‐affected areas ranged from 70 to more than 90% (e.g., Agutu et al., 2017; Masih et al., 2014; Ndehedehe et al., 2019, 2020a).