A Lagrangian Perspective of the Hydrological Cycle in the Congo River Basin

Sorí, Rogert; Nieto, Raquel; Vicente‐Serrano, Sergio M.; Drumond, Anita; Gimeno, Luis

doi:10.5194/esd-2017-21

Cited by 4 publications

(2 citation statements)

References 43 publications

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“…Following the trajectories in a backward mode, we are able to detect the sources of moisture for a selected region where E – P is positive. This methodology for determining the sources of moisture has been extensively used over the past decade both for regional and global studies . The comprehensive review by Ref.…”

Section: Methodsmentioning

confidence: 99%

From Amazonia to southern Africa: atmospheric moisture transport through low‐level jets and atmospheric rivers

Ramos

Blamey

Algarra

et al. 2018

Annals of the New York Academy of Sciences

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A Lagrangian analysis is applied to identify the main moisture source areas associated with atmospheric rivers (ARs) making landfall along the west coast of South Africa during the extended austral winter months from 1980 to 2014. The results show that areas that provide the anomalous uptake of moisture can be categorized into four regions: (1) the South Atlantic Ocean between 10°S and 30°S, (2) a clear local maximum in the eastern South Atlantic, (3) a continental source of anomalous uptake to the north of the Western Cape, and (4) over South America at a distance of more than 7000 km from the target region. It emerges that the South American moisture source can be linked to a particular phase of the South American low‐level jet, known as a no Chaco jet event (NCJE), which transports moisture to the western and central South Atlantic basin. Concisely, we provide strong evidence that the two margins of the South Atlantic Ocean appear connected by two meteorological structures, with the NCJE playing a key role of transporting moisture from South America to the western and central South Atlantic basin, feeding the AR that transports some of the moisture to the west coast of South Africa.

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Section: Methodsmentioning

confidence: 99%

From Amazonia to southern Africa: atmospheric moisture transport through low‐level jets and atmospheric rivers

Ramos

Blamey

Algarra

et al. 2018

Annals of the New York Academy of Sciences

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“…Overestimation by global models (GHM, DGVM, or LSM), even when forced by observed climate, could in general be associated to the underestimation of evaporation due to missing subgrid processes, such as evaporation at the potential rate over saturated areas (marshes, ponds, irrigated fields, and flood plains; Alkama et al, ). Sorí et al () and Dyer et al () recently discussed the high influence that the moisture sources within the Congo River basin can have over the hydrological regime of the river itself.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of Freshwater Flow From Rivers to the Sea in CMIP5 Simulations: Insights From the Congo River Basin

Santini

Caporaso

2018

JGR Atmospheres

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Despite the multisectoral importance of water resources in the context of climate change, it remains still difficult to correctly simulate the terrestrial water cycle via general circulation and Earth system models. While existing model evaluation efforts from the Climate Model Intercomparison Project 5 (CMIP5) are mainly focused on atmospheric variables, we considered here the simulated freshwater flux into the ocean for the river Congo by 20 CMIP5 models. We found that many advancements are still required in global modeling to satisfactorily reproduce the discharge, at least for Congo River. Only the distribution of intermonthly and interannual anomalies of simulated flow, calculated as percent deviations from the respective long‐term average, appears not significantly different from that found in observations. Conversely, most of the models appear to largely overestimate the streamflow seasonal cycle, up to 4–5 times for some months. Further, when looking at severer anomalies in terms of abnormal low‐flow periods (hydrological droughts), the models seem to underestimate their frequency and magnitude while overestimating the duration of deficit conditions with respect to hypothetical water demand. These overall discrepancies between models and observations could propagate in reproducing the land‐ocean feedbacks, as discharge is known to affect sea surface salinity and temperature and, thus, the regional to global ocean circulation and climate. Moreover, biased model‐based discharge simulations could wrongly support water management and infrastructure planning for large river basins, especially when using models instead of measurements, as in case of ungauged rivers, or however when clarification of models' uncertainty is missed.

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Process-based assessment of the impact of reduced turbulent mixing on Congo Basin precipitation in the RCA4 Regional Climate Model

et al. 2021

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In regions featuring strong convective activity (such as the Congo Basin, CB), turbulent mixing in the planetary boundary layer strongly affects the water budget. In this study, we use a process-based evaluation to assess the performance of the Rossby Centre Regional Climate Model (RCM) RCA4 in simulating the September-November CB rainfall, under conditions of strong and weak turbulent mixing. To this regard, results from two different versions of model are analysed: the version used in the COordinated Regional climate Downscaling EXperiment framework (RCA4-v1), and a modified version (RCA4-v4), in which turbulent mixing is reduced. Experiments are driven with boundary conditions from the ERA-Interim reanalysis. Results show that RCA4-v4 improves the CB rainfall climatology compared to RCA4-v1. This result is further related to the models' different representations of the relevant driving mechanisms and processes. The model version with a reduced turbulent mixing (RCA4-v4) shifts less moisture from the lower troposphere towards the free troposphere. As the shallow convective mixing is reduced (owing to the reduction of the turbulent mixing), lower layers are moistened, and low level cloud fraction increases over Equatorial Africa. This increase is stronger over the West Equatorial African (WEA) coast than over the CB. The result is that surface solar radiation decreases more over the WEA coast than over the CB, which would result in a lower surface temperature over WEA coast than over the CB. An enhanced pressure gradient between the WEA and the CB is created as a result, thus enhancing the Congo low level cell, and low level westerlies (LLWs). LLWs are faster, meaning that more moisture flows through the CB Cell, is uplifted in eastern up-branch, and enters African Easterly Jets (AEJs), which, in turn, are intensified due to the increase in the surface temperature gradient. Intensification of the CB cell and mesoscale convective systems (MCSs) is the cause of the higher rainfall and is what improves the CB rainfall climatology in RCA4-v4. In addition, the increase in rainfall causes an increase in soil moisture in RCA4-v4 in both the north and south of the CB. Higher soil moisture does not affect evaporation in the north as soils are already saturated in RCA4-v1. However, the increase in rainfall increases soil moisture in the south in RCA4-v4, which increases evaporation as soils were initially unsaturated. This higher evaporation is exported out of the basin towards Southern Africa, does not recirculate through the Cell, and does not therefore contribute to further improving the rainfall bias over the Congo. Our results show that reducing turbulent mixing results in a better representation of the dynamics of the climate system over the CB and, in turn, improved precipitation.

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A Lagrangian Perspective of the Hydrological Cycle in the Congo River Basin

Cited by 4 publications

References 43 publications

From Amazonia to southern Africa: atmospheric moisture transport through low‐level jets and atmospheric rivers

From Amazonia to southern Africa: atmospheric moisture transport through low‐level jets and atmospheric rivers

Evaluation of Freshwater Flow From Rivers to the Sea in CMIP5 Simulations: Insights From the Congo River Basin

Process-based assessment of the impact of reduced turbulent mixing on Congo Basin precipitation in the RCA4 Regional Climate Model

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