Leading patterns of the satellite-era summer precipitation over West Africa and associated global teleconnections

Nnamchi, Hyacinth C.; Dike, Victor Nnamdi; Akinsanola, A. A.; Okoro, Ugochukwu K.

doi:10.1016/j.atmosres.2021.105677

Cited by 16 publications

(8 citation statements)

References 105 publications

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“…This possibly indicates that those areas act as a bridge connecting drought events in the Sahel and Western Africa 4 . For example, spatial drought propagation from West and Central Africa to the Sahel region is documented in the previous studies 4,52 . Such spatial propagation also establishes a lag-synchronization among the considered regions.…”

Section: Spatial Scale Of Synchronizationmentioning

confidence: 81%

Global droughts connected by linkages between drought hubs

et al. 2023

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Quantifying the spatial and interconnected structure of regional to continental scale droughts is one of the unsolved global hydrology problems, which is important for understanding the looming risk of mega-scale droughts and the resulting water and food scarcity and their cascading impact on the worldwide economy. Using a Complex Network analysis, this study explores the topological characteristics of global drought events based on the self-calibrated Palmer Drought Severity Index. Event Synchronization is used to measure the strength of association between the onset of droughts at different spatial locations within the time lag of 1-3 months. The network coefficients derived from the synchronization network indicate a highly heterogeneous connectivity structure underlying global drought events. Drought hotspot regions such as Southern Europe, Northeast Brazil, Australia, and Northwest USA behave as drought hubs that synchronize regionally and with other hubs at inter-continental or even inter-hemispheric scale. This observed affinity among drought hubs is equivalent to the ‘rich-club phenomenon’ in Network Theory, where ‘rich’ nodes (here, drought hubs) are tightly interconnected to form a club, implicating the possibility of simultaneous large-scale droughts over multiple continents.

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Section: Spatial Scale Of Synchronizationmentioning

confidence: 81%

Global droughts connected by linkages between drought hubs

et al. 2023

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“…Over coastal West Africa, low DC is prominent for all possible networks and cross‐networks (Figure 3). Such a signature may indicate a humid region with localized precipitation events where moisture sources are possibly oceanic (Lélé et al., 2015; Nnamchi et al., 2021). Tropical east Atlantic and the Mediterranean Ocean are the most vital contributors to low‐level moisture supply (Gimeno et al., 2020).…”

Section: Resultsmentioning

confidence: 99%

Quantifying the Precipitation, Evapotranspiration, and Soil Moisture Network's Interaction Over Global Land Surface Hydrological Cycle

Mondal,

Mishra

2024

Water Resources Research

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Enhancing our understanding of the intricate interplay among hydro‐climatic processes is crucial for a comprehensive assessment of water availability and climate extremes across global land regions. Here, we propose an integrated framework to investigate networks of the global fields of multiple hydrological variables (Precipitation, Evapotranspiration, Soil Moisture). We apply a two‐layer complex network concept to formulate the independent networks of each hydrological variable and their interactions. Intra‐ (Single‐layer) and cross‐ (two‐layer) network coefficients are derived from the formulated hydrological network to quantify the linkage, spatial connection density, and scale for the independent hydrological fields (or variables) and their interactions. The joint distribution of the intra‐network coefficients reveals multiple spatial scales of connectivity for a moderately well‐connected location in case of evapotranspiration and soil moisture. With increasing global mean temperature, spatially synchronized evapotranspiration over such a large scale may lead to multi‐continental droughts and heatwaves. Furthermore, the (cross‐) network coefficients have identified regions acting as “bottlenecks” for moisture flow and the water‐dominated areas with less evaporative actions. The contrasting features of two‐layer network coefficients have provided a qualitative picture of moisture circulation and recirculation over many hydrological hotspot regions, such as the Amazonian basin, Indian subcontinents, and the Sahel region. The derived results can be employed to gain insights into the global water cycle’s multiple interacting processes (e.g., land‐atmosphere interactions).

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“…This study focusses on the July-August-September (JAS) season, during which the rainfall variability over the Guinea Coast and the entire West Africa peaks (Nnamchi et al, 2021). Outputs from 31 GCMs participating in CMIP6 are analyzed.…”

Section: Methodsmentioning

confidence: 99%

“…Rainfall changes over the Guinea Coast during the past decades follow the observed decrease of the ATL3 variability (Tokinaga and Xie, 2011;Worou et al, 2020), underlying the strength of the ATL3 impact on the rainfall activity in this area (Nnamchi et al, 2021). Thus, the question arises whether the Atlantic Niño will change in the future and what will the implications be for the tropical hydroclimate, particularly over the Guinea Coast.…”

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confidence: 96%

Weakened impact of the Atlantic Niño on the future equatorial Atlantic and Guinean Coast rainfall

Worou

Goosse

Fichefet

et al. 2021

Preprint

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Abstract. The Guinea Coast is the southern part of the West African continent. Its summer rainfall variability mostly occurs on interannual timescales and is highly influenced by the sea surface temperature (SST) variability in the eastern equatorial Atlantic, which is known as the Atlantic Niño (ATL3). Using historical simulations from 31 General Circulation Models (GCMs) participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we first show that these models are able to simulate reasonably well the rainfall annual cycle in the Guinea Coast, with, however, a wet bias during boreal summer. This bias is associated with too high mean summer SSTs in the eastern equatorial and south Atlantic regions. Next, we analyze the near-term, mid-term and long-term changes of the Atlantic Niño mode relative to the present-day situation, in a climate with a high anthropogenic emission of greenhouse gases. We find a gradual decrease of the equatorial Atlantic SST anomalies associated with the Atlantic Niño in the three periods of the future. This result reflects a possible reduction of the Atlantic Niño variability in the future due to a weakening of the Bjerkness feedback over the equatorial Atlantic. In a warmer climate, an oceanic extension of the Saharan Heat Low over the North Atlantic and an anomalous higher sea level pressure in the western equatorial Atlantic relative to the eastern equatorial Atlantic weaken the climatological trade winds over the equatorial Atlantic. As a result, the eastern equatorial Atlantic thermocline is deeper and responds less to Atlantic Niño events. Among the models that simulate a realistic rainfall pattern associated with ATL3 in the present-day climate, there are 15 GCMs which project a decrease of the Guinean Coast rainfall response related to ATL3, and 9 GCMs which show no substantial change in the patterns associated with ATL3. In these 15 models, the zonal wind response to the ATL3 over the equatorial Atlantic is strongly attenuated in the future climate. Similar results are found when the analysis is focused on the rainfall response to ATL3 over the equatorial Atlantic. There is a higher confidence in the reduction of the rainfall associated with ATL3 over the Atlantic Ocean than over the Guinea Coast. We also found a decrease of the convection associated with ATL3 in the majority of the models.

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Leading patterns of the satellite-era summer precipitation over West Africa and associated global teleconnections

Cited by 16 publications

References 105 publications

Global droughts connected by linkages between drought hubs

Global droughts connected by linkages between drought hubs

Quantifying the Precipitation, Evapotranspiration, and Soil Moisture Network's Interaction Over Global Land Surface Hydrological Cycle

Weakened impact of the Atlantic Niño on the future equatorial Atlantic and Guinean Coast rainfall

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