Abstract
In large freshwater river basins across the globe, the composite influences of large-scale climatic processes and human activities (e.g., deforestation) on hydrological processes have been studied. However, the knowledge of these processes in this era of the Anthropocene in the understudied hydrologically pristine South Central African (SCA) region is limited. This study employs satellite observations of evapotranspiration (ET), precipitation and freshwater between 2002 and 2017 to explore the hydrological patterns of this region, which play a crucial role in global climatology. Multivariate methods, including the rotated principal component analysis (rPCA) were used to assess the relationship of terrestrial water storage (TWS) in response to climatic units (precipitation and ET). The use of the rPCA technique in assessing changes in TWS is warranted to provide more information on hydrological changes that are usually obscured by other dominant naturally-driven fluxes. Results show a low trend in vegetation transpiration due to deforestation around the Congo basin. Overall, the Congo (r2 = 76%) and Orange (r2 = 72%) River basins maintained an above-average consistency between precipitation and TWS throughout the study region and period. Consistent loss in freshwater is observed in the Zambezi (−9.9 ± 2.6 mm/year) and Okavango (−9.1 ± 2.5 mm/year) basins from 2002 to 2008. The Limpopo River basin is observed to have a 6% below average reduction in rainfall rates which contributed to its consistent loss in freshwater (−4.6 ± 3.2 mm/year) from 2006 to 2012.Using multi-linear regression and correlation analysis we show that ET contributes to the variability and distribution of TWS in the region. The relationship of ET with TWS (r = 0.5) and rainfall (r = 0.8) over SCA provides insight into the role of ET in regulating fluxes and the mechanisms that drive precipitation in the region. The moderate ET–TWS relationship also shows the effect of climate and anthropogenic influence in their interactions.
Highlights
Terrestrial water storage (TWS) is a function of changes in the earth’s gravity fields.Its relation to hydrological applications is characterized by the sum of water stored underground, in the soil, as snow, over the land surface, and canopy
Its relevance is due to the complex hydrological characteristics of the South Central African (SCA) region which in turn plays a key role in the climate variability in Africa and the world at large
The statistically significant rotated principal component analysis (rPCA), which are represented by the first six rPCA modes (Figure 3a–f), gave a cumulative variance of 94.51% and were assumed as significant signals denoting over 95% of the total TWS fluctuations over the SCA region
Summary
Terrestrial water storage (TWS) is a function of changes in the earth’s gravity fields.Its relation to hydrological applications is characterized by the sum of water stored underground, in the soil, as snow, over the land surface, and canopy. Terrestrial water storage (TWS) is a function of changes in the earth’s gravity fields. The changes in any of the above components remain one of the most critical elements in the balance of the hydrological cycle. Monitoring the changes that occur within these TWS components is an important hydrological exercise, as it helps in determining the cause of climate change, making a cogent recommendation as to the required environmental response necessary to mitigate potential climatic hazards at the basin or regional scale. With the advent of satellite remote sensing and altimetry, extensive data collection and observation that have been recorded in hydrology, especially in the monitoring of water storage and fluxes in a changing world, enabling a universal evaluation that spans political boundaries [1,2,3].
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