Drought history and vegetation response in the Angolan Highlands

Lourenco, Mauro; Woodborne, Stephan; Fitchett, Jennifer M.

doi:10.1007/s00704-022-04281-4

Cited by 7 publications

(20 citation statements)

References 54 publications

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“…The plateau is 1000–1500 masl and covers over half (65%) of Angola (Huntley, 2019 ). The central highlands of the Bié Plateau are the source water for major drainage basins including the Cuanza, Congo, Zambezi and Okavango (Lourenco et al, 2022a ). The Okavango River catchment is shared by Angola, Namibia and Botswana (McCarthy et al, 2003 ), and it is estimated that over 95% of the water that flows into the Okavango Delta originates from precipitation in the Angolan Highlands (Folwell et al, 2006 ).…”

Section: Methodsmentioning

confidence: 99%

“…The Okavango River catchment is shared by Angola, Namibia and Botswana (McCarthy et al, 2003 ), and it is estimated that over 95% of the water that flows into the Okavango Delta originates from precipitation in the Angolan Highlands (Folwell et al, 2006 ). Precipitation in the Angolan Highlands is seasonal (September–April) with peak rainfall occurring in January (Lourenco et al, 2022a ). This rainwater collects in source lakes that feed the main river channels (Conradie et al, 2016 ).…”

Section: Methodsmentioning

confidence: 99%

“…Average annual precipitation is approximately 1300 mm/year in the Angolan Highlands (Lourenco et al, 2022a ) in comparison to the highly seasonal rainfall (November–March: 300–500 mm/year) of the Okavango Delta (McCarthy et al, 2000 , 2003 ). The Okavango Delta lies within the semi-arid Kalahari Desert of Botswana, where potential evaporation is estimated to be over 2000 mm/year (Gumbricht et al, 2004 ).…”

Section: Methodsmentioning

confidence: 99%

“…The region is the source of nine large hydrographic basins, seven of which are transboundary (Huntley, 2019 ). These river systems originate from the interior Bié Plateau of the Angola Highlands and arise on either side of undulating watersheds that define large river catchments such as the Cuanza, Cassai (Congo), Lungui-Bungu (Zambezi), Cunene, Cuito and Cubango (Okavango: Huntley, 2019 ; Lourenco et al, 2022a ). The Angolan Highlands water tower (AHWT) is the primary source of the Okavango Delta, designated as the 1000 th site to be officially inscribed on the UNESCO World Heritage Site List on 22 June 2014 (UNESCO, 2014 ; Yurco et al, 2017 ).…”

Section: Introductionmentioning

confidence: 99%

“…Scientific and policy debates over human impacts on global freshwater resources have intensified, particularly in the context of growing concerns about the implications of climate change on vulnerable freshwater systems (Bernauer & Böhmelt, 2020 ). Moreover, drought occurrence has increased in the Angolan Highlands (Lourenco et al, 2022a ) and is intensifying in frequency and severity in southern Africa more broadly, presenting challenges to long-term water and food security in the region (Gore et al, 2020 ; Nhamo et al, 2019 ).…”

Section: Introductionmentioning

confidence: 99%

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Defining the Angolan Highlands Water Tower, a 40 plus-year precipitation budget of the headwater catchments of the Okavango Delta

Lourenco

Woodborne

2023

Environ Monit Assess

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Angola is a source of many major rivers in southern Africa and is referred to as the “water tower” of the region. The lack of a defined area delineating the Angolan Highlands water tower (AHWT) limits the conservation of this important freshwater source. This study hydrologically defines the boundary of the AHWT as areas > 1274 m above mean sea level within the Central Bié Plateau of Angola. Using the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) data, this study provides a 41-year precipitation budget of the AHWT and surrounding basins. Between 1981 and 2021, the average annual precipitation over the AHWT was 1112 mm and the gross annual average precipitation volume was approximately 423 km3 over an area of 380,382 km2. The AHWT is the southern source of the Congo Basin, the western source of the Zambezi Basin, and the sole water source of the endorheic Okavango Basin and Okavango Delta, a UNESCO World Heritage Site. On average, approximately 133 km3 (92.36%) of the gross annual precipitation volume for the headwater Cuito and Cubango catchments of the Okavango River is lost before reaching the Okavango Delta. Estimates of the annual flooding of the Okavango Delta during a 35-year period (1985–2019) were correlated to precipitation in the headwater catchments. Correlation coefficients are stronger for the entire rainfall season (0.76) and early rainfall season (0.62) for the combined Cuito–Cubango catchment in comparison to late rainfall season (0.50), which suggests that the antecedent conditions (first and second flood pulse) during the early rainfall season allows for greater Okavango Delta flood inundation. The correlation coefficients between the Cubango (0.72) and Cuito (0.78) Rivers and annual flood inundation are not significantly different (P > 0.05); however, these rivers have fundamental hydrological differences that influence the functioning of the Okavango Delta. The Cubango River, described as a flushing system, has much steeper gradient, more compact and shallow soils and flows faster with significant rapids, whereas the peatland rich, absorbent, seepage-driven baseflow of the Cuito River sustains the Okavango Delta during the dry season. The dynamics of seasonal precipitation, hydrology and climate change in the AHWT have important repercussions on water budgets, food security and biodiversity throughout southern Africa, requiring continued collaboration between countries to ensure that future development is sustainable.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Defining the Angolan Highlands Water Tower, a 40 plus-year precipitation budget of the headwater catchments of the Okavango Delta

Lourenco

Woodborne

2023

Environ Monit Assess

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Drivers of seasonal rainfall variability over the Angolan and Namibian plateaus

Pereira,

Martins,

Fink

et al. 2024

Intl Journal of Climatology

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Southern Africa has been strongly affected by ongoing climate change in recent decades. Rainfall variability is modulated by regional patterns of moisture advection and convergence in the lower troposphere. Using reanalysis, ground and satellite‐based rainfall products and observations from 10 weather stations, we perform a synoptic and climatological analysis focussing on atmospheric circulation, moisture transport and their relationship with rainfall anomalies over the Angolan and Namibian Plateau region. Results clearly show that a stronger (weaker) Zambezi low level jet (LLJ) magnitudes are associated with above (below) normal rainfalls over the main Angolan and Namibian plateaus. With lower confidence, a stronger Limpopo LLJ may also lead to enhanced rainfall over Namibia and southeast Angola. The Zambezi LLJ moisture fluxes are moderately controlled by Mozambique Chanel Trough and Angola Low intensities, while the Limpopo LLJ intensities have very low influence from the Mozambique Chanel Trough and Angola Low, respectively. The Angola Low in its tropical phase is associated with deeper moisture convergence and stronger vertical velocities, leading to higher amounts of precipitable water within the air column, thus enhancing precipitation over the region. It is shown that the major moisture source of rainfall, which is advected to via the Zambezi LLJ, is the Indian Ocean. Meanwhile, the Atlantic Ocean plays a minor role. Given the current lack of observations and projected climate change, further research and investments are urgently needed in the region, for example, regarding the expansion of the surface data network.

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