Modulation of Daily Precipitation over East Africa by the Madden–Julian Oscillation*

2014 ◽  
Vol 27 (15) ◽  
pp. 6016-6034 ◽  
Author(s):  
Fisseha Berhane ◽  
Benjamin Zaitchik
Keyword(s):  
East Africa ◽  
Rainy Season ◽  
Large Scale ◽  
Spatiotemporal Variability ◽  
Climate Projections ◽  
Madden Julian Oscillation ◽  
East African ◽  
Short Rainy Season ◽  
Total Variability ◽  
Short Rains

Abstract Spatiotemporal variability in East African precipitation affects the livelihood of tens of millions of people. From the perspective of floods, flash droughts, and agriculture, variability on intraseasonal time scales is a critical component of total variability. The principal objective of this study is to explore subseasonal impacts of the Madden–Julian oscillation (MJO) on tropospheric circulations affecting East Africa (EA) during the long (March–May) and short (October–December) rains and associated variability in precipitation. Analyses are performed for 1979–2012 for dynamics and 1998–2012 for precipitation. Consistent with previous studies, significant MJO influence is found on wet and dry spells during the long and short rains. This influence, however, is found to vary within each season. Specifically, indices of MJO convection at 70°–80°E and 120°W are strongly associated with precipitation variability across much of EA in the early (March) and late (May) long rainy season and in the middle and late (November–December) short rainy season. In the early short rains (October) a different pattern emerges, in which MJO strength at 120°E (10°W) is associated with dry (wet) spells in coastal EA but not the interior. In April the MJO influence on precipitation is obscured but can be diagnosed in lead time associations. This diversity of influences reflects a diversity of mechanisms of MJO influence, including dynamic and thermodynamic mechanisms tied to large-scale atmospheric circulations and localized dynamics associated with MJO modulation of the Somali low-level jet. These differences are relevant to problems of subseasonal weather forecasts and climate projections for EA.

scholarly journals The Moderate Impact of the 2015 El Niño over East Africa and Its Representation in Seasonal Reforecasts

2019 ◽  
Vol 32 (22) ◽  
pp. 7989-8001 ◽  
Author(s):  
David MacLeod ◽  
Cyril Caminade
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Lower Troposphere ◽  
Eastern Indian Ocean ◽  
East African ◽  
The Indian Ocean ◽  
Short Rains

Abstract El Niño–Southern Oscillation (ENSO) has large socioeconomic impacts worldwide. The positive phase of ENSO, El Niño, has been linked to intense rainfall over East Africa during the short rains season (October–December). However, we show here that during the extremely strong 2015 El Niño the precipitation anomaly over most of East Africa during the short rains season was less intense than experienced during previous El Niños, linked to less intense easterlies over the Indian Ocean. This moderate impact was not indicated by reforecasts from the ECMWF operational seasonal forecasting system, SEAS5, which instead forecast large probabilities of an extreme wet signal, with stronger easterly anomalies over the surface of the Indian Ocean and a colder eastern Indian Ocean/western Pacific than was observed. To confirm the relationship of the eastern Indian Ocean to East African rainfall in the forecast for 2015, atmospheric relaxation experiments are carried out that constrain the east Indian Ocean lower troposphere to reanalysis. By doing so the strong wet forecast signal is reduced. These results raise the possibility that link between ENSO and Indian Ocean dipole events is too strong in the ECMWF dynamical seasonal forecast system and that model predictions for the East African short rains rainfall during strong El Niño events may have a bias toward high probabilities of wet conditions.

East African rails could shape regional links

2016 ◽  
Keyword(s):  
Scale Development ◽  
East Africa ◽  
Red Sea ◽  
Economic Activity ◽  
Large Scale ◽  
Development Projects ◽  
East African ◽  
Content Type ◽  
Economic Ties ◽  
Economic Linkages

Significance The announcement comes as neighbouring Ethiopia moves toward completing a rail link with Djibouti to increase access to the Red Sea port. Ethiopia's rail expansion is part of a rail building spree across East Africa -- a region attempting to improve economic linkages. Impacts Rwanda's renewed relationship with Tanzania will strengthen as economic linkages grow. The trucking industry may attempt to disrupt economic activity if the new railways erode their business. Ethiopia's economic ties with Djibouti will grow as the Red Sea port becomes more accessible. Kenya may need to rethink other large-scale development projects following Ugandan and Rwandan preferences for Tanzanian options.

scholarly journals Investigating Long-Range Seasonal Predictability of East African Short Rains: Influence of the Mascarene High on the Indian Ocean Walker Cell

2020 ◽  
Vol 59 (6) ◽  
pp. 1077-1090
Author(s):  
Xiao Peng ◽  
Scott Steinschneider ◽  
John Albertson
Keyword(s):  
Large Scale ◽  
Walker Circulation ◽  
Lead Times ◽  
East African ◽  
Climate Anomalies ◽  
Mascarene High ◽  
Walker Cell ◽  
Meridional Winds ◽  
The Indian Ocean ◽  
Short Rains

AbstractWe investigate the predictability of East African short rains at long (up to 12 month) lead times by relating seasonal rainfall anomalies to climate anomalies associated with the predominant Walker circulation, including sea surface temperatures (SST), geopotential heights, zonal and meridional winds, and vertical velocities. The underlying teleconnections are examined using a regularized regression model that shows two periods of high model skill (0–3-month lead and 7–9-month lead) with similar spatial patterns of predictability. We observe large-scale circulation anomalies consistent with the Walker circulation at short lead times (0–3 months) and dipoles of SST and height anomalies over the Mascarene high region at longer lead times (7–9 months). These two patterns are linked in time by anticyclonic winds in the dipole region associated with a perturbed meridional circulation (4–6-month lead). Overall, these results suggest that there is potential to extend forecast lead times beyond a few months for drought impact mitigation applications.

scholarly journals The Annual Cycle of East African Precipitation

2015 ◽  
Vol 28 (6) ◽  
pp. 2385-2404 ◽  
Author(s):  
Wenchang Yang ◽  
Richard Seager ◽  
Mark A. Cane ◽  
Bradfield Lyon
Keyword(s):  
East Africa ◽  
Annual Cycle ◽  
Lower Troposphere ◽  
Moisture Flux ◽  
Convective Stability ◽  
East African ◽  
Coupled Models ◽  
Annual Cycles ◽  
Short Rains ◽  
Static Energy

Abstract East African precipitation is characterized by a dry annual mean climatology compared to other deep tropical land areas and a bimodal annual cycle with the major rainy season during March–May (MAM; often called the “long rains”) and the second during October–December (OND; often called the “short rains”). To explore these distinctive features, ERA-Interim data are used to analyze the associated annual cycles of atmospheric convective stability, circulation, and moisture budget. The atmosphere over East Africa is found to be convectively stable in general year-round but with an annual cycle dominated by the surface moist static energy (MSE), which is in phase with the precipitation annual cycle. Throughout the year, the atmospheric circulation is dominated by a pattern of convergence near the surface, divergence in the lower troposphere, and convergence again at upper levels. Consistently, the convergence of the vertically integrated moisture flux is mostly negative across the year, but becomes weakly positive in the two rainy seasons. It is suggested that the semiarid/arid climate in East Africa and its bimodal precipitation annual cycle can be explained by the ventilation mechanism, in which the atmospheric convective stability over East Africa is controlled by the import of low MSE air from the relatively cool Indian Ocean off the coast. During the rainy seasons, however, the off-coast sea surface temperature (SST) increases (and is warmest during the long rains season) and consequently the air imported into East Africa becomes less stable. This analysis may be used to aid in understanding overestimates of the East African short rains commonly found in coupled models.

Modulation of East African boreal fall rainfall: combined effects of the Madden Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO)

2021 ◽  
pp. 1-42
Keyword(s):  
East Africa ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Combined Effects ◽  
Madden Julian Oscillation ◽  
East African

Abstract Climate variabilities can have significant impacts on rainfall in East Africa, leading to disruption in natural and human systems and affecting the lives of tens of millions of people. Subseasonal and interannual variabilities are critical components of total rainfall variability in the region. The goal of this study is to examine the combined effects of the Madden Julian Oscillation (MJO), operating at subseasonal timescale, and the El Niño Southern Oscillation (ENSO), operating at an interannual scale, on the modulation of East African boreal fall (October-November-December; OND) rainfall, commonly called the short rains. Composite analysis shows that daily rainfall responses depend on MJO phase and its interaction with ENSO state. In particular, MJO modulation of rainfall is generally stronger under El Niño conditions relative to ENSO neutral and La Niña conditions, leading to increased potential for daily precipitation excesses during wet MJO phases under El Niño. There is evidence for both dynamic and thermodynamic mechanisms associated with these impacts, including an increase in westerly moisture transport and easterly advection of temperature and moist static energy. Seasonal analysis shows that the frequency and intensity of wet MJO phases during an El Niño contribute notably to the seasonal total precipitation anomaly. This suggests that MJO can mediate El Niño’s impact on OND rainfall in East Africa.

scholarly journals Assessment of climate impact on vegetation dynamics over East Africa from 1982 to 2015

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Wilson Kalisa ◽  
Tertsea Igbawua ◽  
Malak Henchiri ◽  
Shahzad Ali ◽  
Sha Zhang ◽  
...  
Keyword(s):  
East Africa ◽  
Vegetation Dynamics ◽  
Rainy Season ◽  
Linear Trend ◽  
Pearson Correlation ◽  
Climate Factors ◽  
Growth Responses ◽  
Short Rainy Season ◽  
Growth Changes ◽  
The Impact

AbstractLocated across the equator, the East Africa region is among regions of Africa which have previously known the severe vegetation degradation. Some known reasons are associated with the climate change events and unprofessional agricultural practices. For this purpose, the Advanced Very High Resolution Radiometer (AVHRR) version 3 NDVI (NDVI3g) and Climate Research Unit (CRU) datasets for precipitation and temperature were used to assess the impact of climate factors on vegetation dynamics over East Africa from 1982 to 2015. Pearson correlation of NDVI and climate factors were also explored to investigate the short (October - December) rainy seasons. The phenological metrics of the region was also extracted to understand the seasonal cycle of vegetation. The results show that a positive linear trend of 14.50 × 10−4 for mean annual NDVI before 1998, where as a negative linear trend of −9.64 × 10−4 was found after 1998. The Break Point (BP) was obtained in 1998, which suggests to nonlinear responses of NDVI to climate and non-climate drivers. ENSO-vegetation in El-nino years showed a weak teleconnection between ENSO and vegetation growth changes of croplands. Also, the analyzed correlations on NDVI data resulted to the higher correlation between NDVI and precipitation than that with temperature. The Hurst exponent result showed that about, 18.63% pixels exhibited a behavior, typical of random walk (H = 0.5) suggesting that NDVI growth changes may eventually persist, overturn or fluctuate randomly in the future depending on the drivers. Vegetation trends with sustainable (unsustainable) trends were 36.8% (44.6%). Strikingly, about 20% of the total vegetated area showed unsustainable trend from degradation to amelioration. More so, results reveal that the vegetation of the croplands (non-croplands) over East Africa changed insignificantly by 6.9 × 10−5/yr (5.16 × 10−4/yr), suggesting that non-croplands are fast getting reduced Nonetheless, the NDVI growth responses to monthly and seasonal changes in climate were adjudged to be complex and dynamic. Seasonally, the short rainy season showed the higher variability in NDVI than the long rainy season. Also, the DJF, MAM and SON seasons are strongly driven by precipitation variation effect of ENSO versus NDVI series.

scholarly journals Comparison of simulated and reconstructed variations in East African hydroclimate over the last millennium

2016 ◽  
Vol 12 (7) ◽  
pp. 1499-1518 ◽  
Author(s):  
François Klein ◽  
Hugues Goosse ◽  
Nicholas E. Graham ◽  
Dirk Verschuren
Keyword(s):  
Time Series ◽  
Indian Ocean ◽  
East Africa ◽  
Seasonal Cycle ◽  
General Circulation ◽  
Large Scale ◽  
Internal Variability ◽  
General Circulation Models ◽  
Last Millennium ◽  
East African

Abstract. The multi-decadal to centennial hydroclimate changes in East Africa over the last millennium are studied by comparing the results of forced transient simulations by six general circulation models (GCMs) with published hydroclimate reconstructions from four lakes: Challa and Naivasha in equatorial East Africa, and Masoko and Malawi in southeastern inter-tropical Africa. All GCMs simulate fairly well the unimodal seasonal cycle of precipitation in the Masoko–Malawi region, while the bimodal seasonal cycle characterizing the Challa–Naivasha region is generally less well captured by most models. Model results and lake-based hydroclimate reconstructions display very different temporal patterns over the last millennium. Additionally, there is no common signal among the model time series, at least until 1850. This suggests that simulated hydroclimate fluctuations are mostly driven by internal variability rather than by common external forcing. After 1850, half of the models simulate a relatively clear response to forcing, but this response is different between the models. Overall, the link between precipitation and tropical sea surface temperatures (SSTs) over the pre-industrial portion of the last millennium is stronger and more robust for the Challa–Naivasha region than for the Masoko–Malawi region. At the inter-annual timescale, last-millennium Challa–Naivasha precipitation is positively (negatively) correlated with western (eastern) Indian Ocean SST, while the influence of the Pacific Ocean appears weak and unclear. Although most often not significant, the same pattern of correlations between East African rainfall and the Indian Ocean SST is still visible when using the last-millennium time series smoothed to highlight centennial variability, but only in fixed-forcing simulations. This means that, at the centennial timescale, the effect of (natural) climate forcing can mask the imprint of internal climate variability in large-scale teleconnections.

scholarly journals The genus Hypoxis L. (Hypoxidaceae) in the East Tropical

2009 ◽  
Vol 14 (1) ◽  
pp. 1-129 ◽  
Author(s):  
Justyna Wiland-Szymańska
Keyword(s):  
East Africa ◽  
Leaf Anatomy ◽  
Large Scale ◽  
Cultivated Plants ◽  
Vascular Bundles ◽  
East African ◽  
Tropical Africa ◽  
Species Determination ◽  
African Species ◽  
Distribution Maps

The genusHypoxisL. (Hypoxidaceae) in the East TropicalA complete key with full descriptions and distributions of all knownHypoxistaxa found in the East Tropical Africa is presented in the monograph. The morphology of all species, subspecies and varieties is described, including such important taxonomic characters for this genus like tuber flesh color, tunic type, indumentum and seed testa sculpture. A succulent leaf structure is described forH. kilimanjaricavar.prostrata.The anatomical studies were conducted as a part of taxonomical analysis. They have positively evaluated a taxonomic significance of leaf anatomy characters, such as succulent structure, occurrence of bulliform cells in epidermis outside the keel zone, type and distribution of trichomes. The studies of theHypoxisleaf anatomy added new data concerning anatomical differentiation of the cataphylls and the inner leaves. Also differentiated mesophyll and simultaneous presence of different types of stomata on one leaf are reported. It has been shown that in some species mucilage canals are present in the inner leaves and that this character is not constant. The number of vascular bundles, which can be determined only on the basis of a leaf section, is useful only in species with a small number of veins, not increasing with a plant age. Because of lack of constancy in distribution, number of stomata accessory cells cannot be used as a diversifying character for the East African species ofHypoxis.The wax crystals are revealed to exist in many species ofHypoxis.The anatomical characters of scapes were also studied in a taxonomic context. A sclerenchyma distribution, as well as number of vascular bundles can be used for a species determination. The presence of sclerenchyma prevents the scapes from bending down after anthesis. The studies of phenology revealed that there are two groups of taxa, one with a resting period and the other without it. It is connected with a climate in which the species occurs. The study of distribution maps of the species occurring in the East Africa are provided for this area, as well as for their entire range. This new knowledge, along with a revision of literature data, led to a new conclusion as to a number of allHypoxisspecies in Africa, which is now estimated to be 55. The revision demonstrates that distribution of many of theHypoxisspecies is connected with White's phytochoria. It proves that not only South Africa, but also the Zambesian Region is a very important center of diversity of this genus. The number of endemic taxa ofHypoxisfor the East Tropical Africa is very low, including only one species and one subspecies. Additionally, a study of vertical ranges ofHypoxisis presented. It reveals that most of the species in East Africa grow in the mountains and they show preferences of dispersal in particular altitudinal levels. The analysis of the vertical distribution within the entire ranges of different taxa has showed differences in the altitudinal position depending on the geographic location. The human influence onHypoxisis studied in terms of their use in folk medicine and believes. Most of the species ofHypoxissurvive quite well in East Africa, being a visible component of various types of grasslands. Some species however are under threat of extinction. This is due to their incapability of surviving in changed habitats, especially in shade of cultivated plants. Another threat is a large-scale collection of species believed to cure the HIV, or sold as a substitute of similar taxa, assumed to possess such qualities. The IUCN categories are proposed for the East African taxa ofHypoxis.

Onset of the rainy season: a paradigm shift for conservation of the Amazon

2020 ◽  
Author(s):  
Marcos Heil Costa
Keyword(s):  
Rainy Season ◽  
Local Governments ◽  
Large Scale ◽  
Climate Risk ◽  
New Paradigm ◽  
Best Interest ◽  
Double Cropping ◽  
Short Rainy Season ◽  
Forest Code ◽  
Southern Amazonia

<p>It has been recently demonstrated that large-scale mechanisms interact with Amazon deforestation to delay the onset and decrease the duration of the rainy season in Southern Amazonia. A short rainy season increases the exposure of the rainforest to drought and possibly fires, but also increases the climate risk to the intensive double cropping (soy/maize) agriculture system practiced in the region, which requires at least 200 days of rains. Here we show that areas in Southern Amazonia that have more than 20% deforestation, i.e., areas that have not respected the maximum deforestation allowed by Brazil´s Forest Code, have increased climate risk for agriculture when compared to areas that have less than 20% deforested. These results show how environmentally sensible the Brazilian Forest Code is. The legislation, if strictly followed, supports the climate regulation service provided by the rainforest, in a way that benefit the farmers that collectively respect the legislation by anticipating the onset and increasing the duration of the rainy season and decreasing the climate risk to the double cropping systems. These results introduce a new paradigm for conservation of the Amazon, in which there are economic and social reasons to preserve the native vegetation, and it is in the best interest of the agribusiness, local governments and people, to conserve and restore the remaining natural vegetation.</p>

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