The quasi-periodic behavior of rainfall variability in Africa and its relationship to the southern oscillation

1986 ◽  
Vol 34 (3-4) ◽  
pp. 311-348 ◽  
Author(s):  
Sharon E. Nicholson ◽  
Dara Entekhabi
Keyword(s):  
Southern Oscillation ◽  
Rainfall Variability ◽  
Periodic Behavior

scholarly journals Climatology of Heavy Orographic Rainfall Induced by Tropical Cyclones over Madagascar: From Synoptic to Mesoscale Perspectives

2016 ◽  
Vol 5 (2) ◽  
pp. 132 ◽  
Author(s):  
Tatiana A. Arivelo ◽  
Yuh-Lang Lin
Keyword(s):  
Tropical Cyclones ◽  
Southern Oscillation Index ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Eastern Coast ◽  
Quasi Biennial Oscillation ◽  
Trade Winds ◽  
Southwest Indian Ocean ◽  
The North ◽  
Orographic Rainfall

Variability of and generation mechanisms for Madagascar rainfall are studied by conducting climatological, synoptic and mesoscale analyses. It is found the rainfall variability is highly sensitive to seasons with high variability in summer (Nov-Apr). The rainfall in summer is controlled by the Intertropical Convergence Zone (ITCZ) and orographic rainfall associated with tropical cyclones (TCs), while the rainfall in winter (May-Oct) is controlled by trade winds and local orographic rainfall along the eastern coast. Synoptic analysis reveals that major climate variations in summer are associated with ITCZ position, which is closely related to TC genesis locations and quasi-biennial oscillation (QBO). Linkages between El-Niño Southern Oscillation Index (ENSO) and Southern Oscillation Index (SOI) are identified as the cause of inconsistent dry or wet summers. Mesoscale analysis depicts the importance of the orographic effects on prevailing wind, which are controlled by the orography in both seasons. In winter, the prevailing trade winds over the Southwest Indian Ocean are from the east and are split to the north and south when it impinges on Malagasy Mountains. On the other hand, in summer the prevailing easterlies are weaker leading to the production of lee vortices, in addition to the flow splitting upstream of the mountain. Thus, the flow is classified into two regimes: (a) flow-over regime with no lee vortices under high Froude number (Fr=1.2-1.8) flow, and (b) flow-around regime with lee vortices under low Fr (=0.88-1.16) flow. A case study of TC Domoina (1984) indicates that the long-lasting heavy rainfall was induced by the strong orographic blocking of Madagascar. The shorter-term (e.g., 2 days) heavy orographic precipitation is characterized by large VH ∙Ñh which is composed by two common ingredients, namely a strong low-level wind normal to the mountain (VH) and a steep mountain slope (∇h).

scholarly journals Teleconnections between Monthly Rainfall Variability and Large-Scale Climate Indices in Southwestern Colombia

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1863 ◽  
Author(s):  
Teresita Canchala ◽  
Wilfredo Alfonso-Morales ◽  
Wilmar Loaiza Cerón ◽  
Yesid Carvajal-Escobar ◽  
Eduardo Caicedo-Bravo
Keyword(s):  
Water Resources ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Monthly Rainfall ◽  
Wavelet Coherence ◽  
Climate Indices ◽  
Annual Scale ◽  
Wavelet Coherence Analysis

Given that the analysis of past monthly rainfall variability is highly relevant for the adequate management of water resources, the relationship between the climate-oceanographic indices, and the variability of monthly rainfall in Southwestern Colombia at different time scales was chosen as the research topic. It should also be noted that little-to-no research has been carried out on this topic before. For the purpose of conducting this research, we identified homogeneous rainfall regions while using Non-Linear Principal Component Analysis (NLPCA) and Self-Organizing Maps (SOM). The rainfall variability modes were obtained from the NLPCA, while their teleconnection in relation to the climate indices was obtained from Pearson’s Correlations and Wavelet Transform. The regionalization process clarified that Nariño has two regions: the Andean Region (AR) and the Pacific Region (PR). The NLPCA showed two modes for the AR, and one for the PR, with an explained variance of 75% and 48%, respectively. The correlation analyses between the first nonlinear components of AR and PR regarding climate indices showed AR high significant positive correlations with Southern Oscillation Index (SOI) index and negative correlations with El Niño/Southern Oscillation (ENSO) indices. PR showed positive ones with Niño1 + 2, and Niño3, and negative correlations with Niño3.4 and Niño4, although their synchronous relationships were not statistically significant. The Wavelet Coherence analysis showed that the variability of the AR rainfall was influenced principally by the Niño3.4 index on the 3–7-year inter-annual scale, while PR rainfall were influenced by the Niño3 index on the 1.5–3-year inter-annual scale. The El Niño (EN) events lead to a decrease and increase in the monthly rainfall on AR and PR, respectively, while, in the La Niña (LN) events, the opposite occurred. These results that are not documented in previous studies are useful for the forecasting of monthly rainfall and the planning of water resources in the area of study.

Elemental proxy evidence for late Quaternary palaeoenvironmental change in southern African sedimentary records: interpretation and applications

2021 ◽  
Author(s):  
M.S. Humphries
Keyword(s):  
Environmental Change ◽  
Southern Africa ◽  
Southern Oscillation ◽  
Late Quaternary ◽  
Rainfall Variability ◽  
Analytical Techniques ◽  
Summer Rainfall ◽  
Geochemical Data ◽  
Complex Nature ◽  
Cape Coast

Abstract Sediments are the most important source of Late Quaternary palaeoclimate information in southern Africa, but have been little studied from a geochemical perspective. However, recent advances in analytical techniques that allow rapid and near-continuous elemental records to be obtained from sedimentary sequences has resulted in the increasing use of elemental indicators for reconstructing climate. This paper explores the diverse information that can be acquired from the inorganic component of sediments and reviews some of the progress that has been made over the last two decades in interpreting the climatic history of southern Africa using elemental records. Despite the general scarcity of elemental records, excellent examples from the region exist, which provide some of the longest and most highly resolved sequences of environmental change currently available. Records from Tswaing crater and marine deposits on the southern KwaZulu-Natal coastline have provided rare glimpses into hydroclimate variability over the last 200 000 years, suggesting that summer rainfall in the region responded predominantly to insolation forcing on glacial-interglacial timescales. Over shorter timescales, lakes and wetlands found in the Wilderness embayment on the southern Cape coast and along the Maputaland coast in north-eastern South Africa have yielded highly-resolved elemental records of Holocene environmental change, providing insight into the changing interactions between tropical (e.g., El Niño-Southern Oscillation) and temperate (e.g., mid-latitude westerlies) climate systems affecting rainfall variability in the region. The examples discussed demonstrate the multiple environmental processes that can be inferred from elemental proxies and the unique insight this can provide in advancing our understanding of past climate change on different timescales. The interpretation of geochemical data can be complicated by the complex nature of sedimentary environments, various proxy assumptions and analytical challenges, and the reliability of sediment-based climate reconstructions is substantially enhanced through multi-proxy approaches.

On the Relation between Hydrological Forecasts and Water Resources Management

2010 ◽  
pp. 229-243
Author(s):  
Tarig El Gamri ◽  
Amir B. Saeed ◽  
Abdalla K. Abdalla
Keyword(s):  
Water Resources ◽  
Water Conservation ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Rain Gauge ◽  
Enso Event ◽  
Discharge Data ◽  
Dry Zone ◽  
High Prediction ◽  
Management Approaches

Seasonal streams (wadis) are of vital importance in dry and semidry countries including Sudan. Depending on the rainfall variability of the country, the annual discharge of such wadis was estimated to range from 3 to 7 km3 per annum. In the present study two wadi-discharge prediction methodologies were used to predict the discharge of Khor (wadi) Abu Fargha. The first methodology depends on the El Nino Southern Oscillation (ENSO) event which was divided into six distinct stages. The discharge during each stage was compared to previously estimated rainfall in the dry zone of the Sudan during the concurrent stage. The methodology was found to illustrate about 83% of the discharge behaviour of Khor Abu Fargha. This high prediction skill is attributed to the fact that the wadi is located in an area that is influenced by the ENSO event and to the availability of the discharge data for consecutive 34 years. The use of global sea surface temperatures (SSTs) in rainfall seasonal forecast studies was initiated during the 1990s through the development of empirical-statistical models. Using such methodology the models predicting Abu Fargha discharges were found to excel those for some meteorological stations and the dry zone of the Sudan as well. This is attributed to the fact that wadi discharges represent the whole catchment area whereas rainfall data represent only the rain gauge readings. The models using May global SSTs achieved better predictability in Abu Fargha discharges the thing which was found to be consistent with the results obtained in previous studies by Kassala meteorological station which is located in the vicinity of the wadi. The chapter illustrates the use of the wadi prediction information in forecasting the available storage of the aquifers and concluded that combining the different information, realistic management of surface and ground water resources can be achieved. The study recommended the use of water conservation techniques and integrated dryland management approaches.

scholarly journals Interdecadal Changes in the Leading Ocean Forcing of Sahelian Rainfall Interannual Variability: Atmospheric Dynamics and Role of Multidecadal SST Background

2018 ◽  
Vol 31 (17) ◽  
pp. 6687-6710 ◽  
Author(s):  
Roberto Suárez-Moreno ◽  
Belén Rodríguez-Fonseca ◽  
Jesús A. Barroso ◽  
Andreas H. Fink
Keyword(s):  
Southern Oscillation ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Rain Gauge ◽  
Sst Variability ◽  
Cold Events ◽  
Sahel Rainfall ◽  
West African Sahel ◽  
First Time

The atmospheric response to global sea surface temperatures is the leading cause of rainfall variability in the West African Sahel. On interannual periodicities, El Niño–Southern Oscillation, the Atlantic equatorial mode, and Mediterranean warm/cold events primarily drive variations of summer rainfall over the Sahel. Nevertheless, the rainfall response to these modes of interannual SST variability has been suggested to be unstable throughout the observational record. This study explores changes in the leading patterns of covariability between Sahel rainfall and SSTs, analyzing the dynamical mechanisms at work to explain the nonstationary relationship between anomalies in these two fields. A new network of rain gauge stations across West Africa is used for the first time to investigate these instabilities during the period 1921–2010. A hypothesis is raised that the underlying SST background seems to favor some interannual teleconnections and inhibit others in terms of the cross-equatorial SST gradients and associated impacts on the location of the intertropical convergence zone. Results of this study are relevant for improving the seasonal predictability of summer rainfall in the Sahel.

scholarly journals Cereal Production Trends under Climate Change: Impacts and Adaptation Strategies in Southern Africa

Agriculture ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 30 ◽  
Author(s):  
Luxon Nhamo ◽  
Greenwell Mathcaya ◽  
Tafadzwanashe Mabhaudhi ◽  
Sibusiso Nhlengethwa ◽  
Charles Nhemachena ◽  
...  
Keyword(s):  
Food Security ◽  
Southern Africa ◽  
Crop Production ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
International Aid ◽  
Adaptation Strategies ◽  
Irrigated Agriculture ◽  
Cereal Production ◽  
The Impact

The increasing frequency and intensity of droughts and floods, coupled with increasing temperatures and declining rainfall totals, are exacerbating existing vulnerabilities in southern Africa. Agriculture is the most affected sector as 95% of cultivated area is rainfed. This review addressed trends in moisture stress and the impacts on crop production, highlighting adaptation possible strategies to ensure food security in southern Africa. Notable changes in rainfall patterns and deficiencies in soil moisture are estimated and discussed, as well as the impact of rainfall variability on crop production and proposed adaptation strategies in agriculture. Climate moisture index (CMI) was used to assess aridity levels. Southern Africa is described as a climate hotspot due to increasing aridity, low adaptive capacity, underdevelopment and marginalisation. Although crop yields have been increasing due to increases in irrigated area and use of improved seed varieties, they have not been able to meet the food requirements of a growing population, compromising regional food security targets. Most countries in the region depend on international aid to supplement yield deficits. The recurrence of droughts caused by the El Niño Southern Oscillation (ENSO) continue devastating the region, affecting livelihoods, economies and the environment. An example is the 2015/16 ENSO drought that caused the region to call for international aid to feed about 40 million people. In spite of the water scarcity challenges, cereal production continues to increase steadily due to increased investment in irrigated agriculture and improved crop varieties. Given the current and future vulnerability of the agriculture sector in southern Africa, proactive adaptation interventions are important to help farming communities develop resilient systems to adapt to the changes and variability in climate and other stressors.

scholarly journals Characterization of West African Jet Streams and Their Association to ENSO Events and Rainfall in ERA-Interim 1979–2011

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Churchill Okonkwo ◽  
Belay Demoz ◽  
Sium Tesfai
Keyword(s):  
Decadal Variability ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
West African ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Jet Streams ◽  
Enso Events ◽  
Westerly Jet ◽  
Sahel Region

The interannual variability of West African jet streams and their association with rainfall are reexamined using European Reanalysis ERA-Interim 1979–2011. The objective of the study is to characterize their climatology and role in rainfall variability in western Sahel. Wavelet analysis was used on wind speed data and implications to ENSO were discussed subsequently. Our results show that while the low-level African Westerly Jet (AWJ) correlates well with rainfall south of the equator in boreal winter months, the Tropical Easterly Jet (TEJ) and African Easterly Jet (AEJ) correlate better with rainfall north of the equator in the boreal summer months. Results of interannual-to-decadal variability in 200 mb, 600 mb, and 850 mb of zonal wind reveal that there is enhanced variability in the 2–8 year band. Also, the TEJ, AEJ, and AWJ fluctuations are coupled with variations in southern oscillation. Further analysis suggests a statistically significant association between TEJ and the El Niño events of the 1980s that led to intense drought in the Sahel region of West Africa. The 2007 moderate La Niña shows a statistically significant coherence with the 500 mb, 600 mb, and 850 mb jets. These associations are also phase locked, suggesting that the association may be more than by chance.

Including climatic variability in stochastic rainfall for flood catastrophe modelling – The effect of ENSO and SOI in China

2020 ◽  
Author(s):  
Jose Luis Salinas ◽  
Rebecca Smith ◽  
Shuangcai Li ◽  
Ludovico Nicotina ◽  
Arno Hilberts
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Climatic Variability ◽  
Extreme Rainfall ◽  
Extreme Rainfall Events ◽  
Natural Catastrophes ◽  
Socio Economic Impact ◽  
Catastrophe Modelling

<p>Damages from flooding in China account on average for 60-70% of the total Annual Losses derived from natural catastrophes. The extreme rainfall events responsible for these inundations can be broadly categorised in two well differentiated mechanisms: Tropical Cyclone (TC) induced, and non Tropical Cyclone induced (nonTC) precipitation. Between 2001 and 2015, inland nonTC rainfall flood events occurred roughly with double the frequency as TC events. While TC events can be highly destructive for coastal locations, over the entire China territory nonTC flooding accounted for more than half of the total economic flood loss for events with significant socio-economic impact, highlighting the importance of the nonTC flooding mechanism on the regional and national scale.</p><p>Large-scale modes of climate variability modulate in different ways TC and nonTC induced precipitation, both in the frequency and the magnitude of the events. In a stochastic rainfall generation framework, it becomes therefore useful to model these two mechanisms separately and include their differentiated long-term climatic influences in order to fully reproduce the overall observed rainfall variability. This work presents results on the effect of ENSO and Southern Oscillation Index (SOI) values on seasonal rainfall in China, and how to include this climatic variability in stochastic rainfall for flood catastrophe modelling.</p>

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