Rain in Western Cape during winter. (2018) and Mahlalela et al. The SWC is characterized by a mediterranean climate and is part of the austral winter rainfall region of Southern Africa. Figure S5 Latitude‐height cross section of March–May zonal wind (m⋅s–1) anomalies in 2015–2017 for days characterized by the SOM circulation states. It appears that the lower rainfall in the drought years was from both a reduction in the number of rain‐bearing synoptic states and the reduction in the amount of rain falling when these states did occur. Consequently, people living in this region will become vulnerable to water scarcity and land degradation (Feng and Fu, 2013). Water table rises and periodic rivers flow. 4 x2 (8) 1.2.5 In a paragraph of approximately EIGHT lines, explain the influence of mid latitude cyclones in the western Cape. This suggests that the significant upward (downward) trend of dry (wet) circulation types in most seasons (including winter) during 1979–2009 over Cape Town, reported by Lennard and Hegerl (2015) at one Cape Town station, might have continued until 2017, affecting the rainfall frequency associated with these circulation types. @$W4�d3��4�� &9��= �����$��x����������"�?×_ �_ Additionally, the decrease of CAPE, during the drought may have helped reduce the convective potential over the SWC, further suppressing rainfall. 1.3.5 How will the movement of mid-latitude cyclone C be influenced by anticyclone B? In March and April (transitional regime), there was a higher frequency of states occurring typically in winter, including the low‐pressure systems associated with cold front and thus rainfall over SWC (node 6). While that study provides essential information on the likelihood of the event and the contribution of anthropogenic climate change to its occurrence from the perspective of rainfall as a surface expression of the state of the climate system, it did not explicitly address the dynamical processes behind the 2015–2017 SWC drought. Cape Town experiences a mediterranean climate with distinctive seasonal weather processes. If you do not receive an email within 10 minutes, your email address may not be registered, The adjacent interior (Karoo) has sparse vegetation fronted by coastal mountains over 1 000 m. ... atmospheric impact of 4 million residents and their resource needs (cf. Figure S6 Latitude‐height cross section of June–July zonal wind (m⋅s–1) anomalies in 2015–2017 for days characterized by the SOM circulation states. The southwestern tip of the country has a Mediterranean climate, with hot dry summers and cool wet winters. This paper examines the density, distribution and characteristics of mid‐latitude cyclones in the oceans south of Africa in the GENESIS general circulation model (GCM). influence the direction of movement of mid-latitude cyclones. h�b```�e���� ��ea�X �``���������F��� �?�E���rP��h�n�F�"����,�����*�ԺAc� ������ 2:4`K>�F�0��|�b@,v�Б��hiP�����'C�ց�|��4� �. Also, Lehner et al. 2 Global air circulation. G D Samaai - DCES Geography. This process enhances drying particularly over the mountainous areas. While rainfall in the core of the winter rainfall season (June–July: “JJ”) was near or above normal, in the shoulder season months (March–May: “MAM” and August–October: “ASO”), rainfall was below normal in 2015 and 2017, and near normal in 2016. GAUTENG DEPARTMENT OF EDUCATION. Books for Download . In March, April, and October, the highest frequency of occurrence of the synoptic types is located in the centre of the SOM array, reflecting the domination of transitional circulation types over the SWC (Figure 4). Mid- latitude cyclones: Characteristics, Development stages, Weather patterns and Impact discussed. This causes rainfall over the South Western Cape in winter. (1) 2009 Geography Grade 12 Paper 1 3 ... are concerned about the impact that the grazing land, the factory and the agricultural land could have on the river. SOM is an artificial neural network‐based cluster analysis that identifies frequently occurring spatial patterns in multidimensional datasets by clustering and reducing their initial dimensions (Kohonen, 1990, 2013; Vesanto and Alhoniemi, 2000; Johnson, 2013). The area shaded in black in (b) on the horizontal axis represents the drought period (2015–2017). The first is the decrease in the occurrence frequency of synoptic circulation states associated with rain‐bearing frontal systems over the SWC and the increased frequency of dry and transitional circulation types. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Anthropogenic influence on the drivers of the Western Cape drought 2015–2017, The influence of ENSO on winter rainfall in South Africa, Drought Policy Brief: Western Cape Agriculture, Relationships between South Atlantic SST variability and atmospheric circulation over the South African region during austral winter, Links between the Antarctic oscillation and winter rainfall over western South Africa, Global memory analysis in observed and simulated CAPE and CIN, The self‐organizing map in synoptic climatological research, Projected changes in mean and extreme precipitation in Africa under global warming. The SWC receives most of its rainfall, about 60–70%, during the winter months (June–August or JJA) (Reason and Jagadheesha, 2005), when the two subtropical anticyclones move northwards, enabling the strengthening and the northward expansion of the westerlies, and resulting in the rain‐bearing frontal systems associated with mid‐latitude cyclones moving across the SWC. 5 Tropical Cyclones. 2.1.5 A change in the wind direction associated with a mid-latitude cyclone in the Northern Hemisphere is referred to as (backing/veering). The drought and the associated water crisis had large socio‐economic impacts at national and local levels. What is a mid-latitude cyclone? However, node 27, a climatologically dry node, was wetter than normal during the drought (Figure S1), which may probably be associated with cut‐off lows (Abba Omar and Abiodun, 2020). The southward shift of westerlies and the persistence of high pressure over the region also influenced atmospheric moisture, which decreased during the drought years, especially in the shoulder seasons over the region. (2019) linked the drought to a long‐term decrease in rainfall events during cold fronts over the Western Cape region. (1 x 2) (2) 3.6 Name TWO effects of mid-latitude cyclones on farming in the South-western Cape. 1 Changes in Energy balance. For example, like total rainfall, CAPE increased in rain‐bearing circulation types in April (nodes 4–6), while it decreased in May (Figures 4 and 8). This study analysed the frequency of circulation types, rainfall characteristics, along with associated local moisture flux and CAPE, during the 2015–2017 drought over the SWC compared to the previous (1981–2010) years. Hence, for a better drought management and effective planning in the future, there is a need to … Gale-force south-westerly winds are expected between Plettenberg Bay and East London, with very rough seas from Lamberts Bay to East London. Given the dominance of that mechanism, the variability of winter rainfall in the SWC depends on drivers affecting the position, strength, and frequency of these westerly cyclones. If the upper levels are favorable, then the mid-latitude cyclone will continue to develop and bring up mT air in the warm sector and bring down cP air in the cold sector. This allowed us to identify the dominant synoptic states over Southern Africa that influence the local climate in the area affected by the drought. and their impact on the communities and their livelihoods. tropical easterly and mid-latitude westerly wind regimes, and has a semi-arid, rainy-winter climate. Figure S3 Latitude‐height cross section of June–July moisture flux (g⋅kg–1⋅m⋅s–1) anomalies in 2015–2017 for days characterized by the SOM circulation states. We first apply the SOM algorithm to reanalysis datasets to identify the synoptic circulation states over Southern Africa and examine how they relate to rainfall characteristics over the SWC in South Africa during the 2015–2017 drought. Statistical recalibration of GCM forecasts over southern Africa using model output statistics, Projected drought risk in 1.5°C and 2°C warmer climates, Relating changes in synoptic circulation to the surface rainfall response using self‐organising maps, Synoptic‐based evaluation of climatic response to vegetation change over southern Africa, Mechanisms behind early winter rainfall variability in the southwestern Cape, South Africa, Probabilistic predictions of climate change for Australia and southern Africa using the reliability ensemble average of IPCC CMIP3 model simulations, Climate Change 2014: Impacts, Adaptation, and Vulnerability. To identify the synoptic circulation patterns over Southern Africa associated with rainfall over the SWC in South Africa, we applied self‐organizing maps (SOMs) analysis to ERAINT daily 850 hPa geopotential height datasets using all days from March to October for the period 1979–2017 over a small Southern African domain extending from 0° to 34.5°E and 19.5 to 45°S. Figure S2 Latitude‐height cross section of March–May moisture flux (g⋅kg–1⋅m⋅s–1) anomalies in 2015–2017 for days characterized by the SOM circulation states. Contribute Now. (2019), who reported a link between rain‐bearing fronts and rainfall duration over the SWC. The westerly wave manifests strongly in winter circulation, with a cyclical transition in the vicinity of the African continent between the low pressure system associated with the mid‐latitude cyclones (node 6), followed by southerly meridional flow (node 30), a ridging high pressure system connecting Atlantic and Indian Ocean lows (node 25) and circulation dominated by subtropical highs at the wave's trough (node 1). h�bbd```b``���A$��""Y��"�`2,�fk�I}�a}�� Q�.? Also, Burls et al. These results ... strongest positive score is calculated for Polokwane (m = 1.79), located in the northern interior of southern Africa (Fig. When do mid-latitude cyclones form. Latitudinal position also allows the influence of mid-latitude cyclones. Total annual rainfall in each of the 2015–2017 years was lower than the long‐term average, with the strongest anomaly in 2017 (Figure 1b), both in our station data, GPCC, and ERAINT. associated weather conditions of a mid-latitude cyclone. The multi‐year (2015–2017) drought in the South West of the Western Cape (SWC) caused a severe water shortage in the summer of 2017–2018, with damaging impacts on the local and regional economy, and Cape Town being in the news one of the first major cities to potentially run out of water. This agrees with Burls et al. Results in a coastal low which cause Berg Winds. They associated these changes in rainfall characteristics to Hadley Cell expansion over the Southern Hemisphere and to the upward trend in high‐pressure conditions in days following the passage of a frontal system. The total rainfall anomaly in the shoulder seasons was caused by a combination of the lower frequency of rain‐days and lower intensity of daily rainfall events (Figure 1d,e). Here, we assess the links between the rainfall deficits during the drought and (a) large scale circulation patterns, (b) moisture transport, and (c) convective available potential energy (CAPE). Also, the rainfall associated with rain‐bearing circulation types decreased during the 2015–2017 drought due to a southward shift in westerlies and less moisture influx into the SWC region. Learn more. (2018) to assess rainfall variability over Cape Town based on SOMs. Any queries (other than missing content) should be directed to the corresponding author for the article. In most wet nodes (5, 6, and 10–12) the positive moisture flux anomaly is located south of the SWC over the ocean while, in nodes 17 and 18, there were no latitudinal shifts, simply a reduction in overall flux (Figure 6). Climate System Analysis Group, University of Cape Town, Cape Town, South Africa, School of International Development, University of East Anglia, Norwich, NR4 7TJ, United Kingdom, Funding information: AXA Research Fund; BNP Paribas Climate Foundation; Department of Science and Technology (South Africa); National Research Foundation (South Africa); Southern African Systems Analysis Centre. 3716 0 obj <>/Filter/FlateDecode/ID[<6783D72ED3200A4594DB26A06E7748CC>]/Index[3692 38]/Info 3691 0 R/Length 114/Prev 272968/Root 3693 0 R/Size 3730/Type/XRef/W[1 3 1]>>stream Existing attempts to reconstruct latitudinal shifts in the ... archaeological site in the Western Cape of South Africa is used to assess the validity of the method. On a monthly basis, the anomaly manifested differently between seasons, but the pattern of seasonal anomalies was similar between years (Figure 1c). July and August had a higher frequency of transitional regime states characterized by the more southerly position of the mid‐latitude low pressure and the westerlies (nodes in the bottom‐central part of the SOM). Grade 12. GEOGRAPHY. A total of 22 rainfall stations (Figure 1a) passed these quality criteria and were analysed in this study. Other factors shown to affect SWC rainfall include local SST anomalies (Reason and Jagadheesha, 2005) and sea ice anomalies (Blamey and Reason, 2007). The Antarctic Oscillation (AAO)—also called Southern Annular Mode (SAM)—which expresses pressure difference between mid‐ and low‐latitudes, and thus indirectly influences the latitudinal position of the westerlies, has a strong influence on core winter rainfall over western South Africa. How severe is Cape Town's “Day Zero” drought? We would also like to acknowledge the Southern African Systems Analysis Centre (SASAC) and funding provided by the South African National Research Foundation (NRF) and Department of Science and Technology (DST). This study identifies and characterizes the anomalies in atmospheric circulation as well as anomalies in rainfall responses to the synoptic forcing during the 2015–2017 SWC drought. Also, in March–June, August, and October rainfall decreased (Figures 4 and S1) in most nodes with transitional circulation types together with CAPE (Figure 8). 3.5 Give the term used to describe a series of mid-latitude cyclones passing over an area in quick succession. In that, we extend studies by Sousa et al. Part I: southern Africa, The ‘Day Zero’ Cape Town drought and the poleward migration of moisture corridors, The Weather and Climate of Southern Africa. Also, there are some differences in rain days per node day between months—for a number of “drier” circulation patterns (nodes 20, 26, 27), there are fewer rain days in the transitional seasons than when those conditions occur in core winter (JJA). ePortal . The first of those studies shows the strong influence of AAO (positive phase) and the associated poleward shift of moisture transport corridors (atmospheric rivers) due to the latitudinal expansion of the two subtropical high‐pressure systems in the South Atlantic and Indian Oceans. The arrows represent the moisture flux (g⋅kg, Observed total monthly rainfall (mm.month, Frequency of occurrence of SOM nodes shown in Figure, Fraction of rain days per node‐days, that is, days characterised by the circulation states represented in Figure, Latitude‐height cross‐section of moisture flux (g⋅kg, Latitude‐height cross‐section of zonal wind (m⋅s, Convective available potential energy (CAPE, J⋅kg, Dynamics of The Tropical Atmosphere and Oceans, Meteorological Measurements and Instrumentation, Fluid Dynamics of the Mid-Latitude Atmosphere, Time Series Analysis in Meteorology and Climatology: An Introduction, The Atmosphere and Ocean: A Physical Introduction, 3rd Edition, Quarterly Journal of Royal Meteorological Society Special Collections, Meteorological Applications Special Collections, I have read and accept the Wiley Online Library Terms and Conditions of Use, Characteristics of cut‐off lows during the 2015–2017 drought in the Western Cape, South Africa, Relationships between Antarctic sea‐ice and South rainfall, African winter, Drought characteristics over the Western Cape Province, South Africa, The Cape Town “day zero” drought and Hadley cell expansion, DEA (Department of Environmental Affairs), The ERA‐Interim reanalysis: configuration and performance of the data assimilation system, Expansion of global drylands under a warming climate, Eurasian October snow water equivalent: using self‐organizing maps to characterize variability and identify relationships to the MJO, Self‐organizing maps: applications to synoptic climatology. However, as populations increase - with the consequence that the built environment increases in size - coupled with the effects of climate variability, there emerges greater ... by the Western Cape Provincial Minister of Local Government, Environmental Affairs and Development Planning The Western Cape can be regarded as one of the most disaster … Climate projections over Southern Africa indicate that the region will become drier, with significant expansions of arid and semi‐arid zones due to global warming (Feng and Fu, 2013; Cook et al., 2014; Niang et al., 2014; Lehner et al., 2017). During the 2015–2017 drought, winter months were particularly characterized by persistent high‐pressure fields with frequent ridging of the two SAH and SIH over the sub‐continent suppressing rainfall (intensity, frequency, and duration) over the SWC. Positive: provide rain for agriculture increase yield and income ... damage to houses, stock losses and damage to crops costly repairs and aid projects. Positive: rain to sustain natural vegetation and indigenous animals … 1.3.3 Why are satellite images of mid-latitudes cyclone useful? In this study, we used surface station observations and reanalysis datasets. The fear of running out of water—called “Day Zero” in the media—before the onset of the winter rainfall season of 2018 forced the City of Cape Town to impose severe restrictions on water usage, and to implement emergency supply augmentation measures. A mid-latitude cyclone was present. Lennard and Hegerl (2015) examined the relationship between changes in synoptic‐scale circulation and rainfall response under winter and summer rainfall regimes in South Africa using SOMs. Philippon et al. Figures S1 and 5 with Figure 3), i.e., the highest intensity and frequency is associated with node 6, moderate values with the top‐right, and lowest or null values with the top‐left and left‐hand side section of the SOM array. During the 2015–2017 drought, there was a general decrease in CAPE over the SWC across the SOM nodes (Figures 8 and S8). Mid- latitude cyclones: Characteristics, Development stages, Weather patterns and Impact discussed. %PDF-1.5 %���� (2014) projected an increased risk of multi‐year severe droughts in these regions during the 21st century. Their findings suggest that an increased cut‐off lows‐related rainfall in 2015 and 2016 reduced the severity of the drought. Learn about our remote access options, African Climate and Development Initiative, University of Cape Town, Cape Town, South Africa. The observational dataset comprises rainfall station records covering the SWC obtained from the South African Weather Service (SAWS). (2019) who identified longer‐term drought trends linked to the combined influence of a long‐term (1910–2017) decrease of rainfall day frequency associated with a more recent (1979–2017) deficit in rainfall intensity. The … Phase 1: Overberg DM Sea Level Rise and Flood Risk Literature Review 2012 ... with most rain occurring between May and August from mid-latitude cyclone cold fronts, while minor rain occurs in spring and autumn from cut off low pressure systems. There seem to be higher rainfall intensities associated with the same circulation patterns occurring in July than in other months. In order to disentangle the effects on rainfall anomaly of change in frequency of synoptic states as captured by SOM from other (thermodynamic) effects, we illustrate climatological and drought‐period characteristics of rainfall on “node days”. In May, the contribution of the “wettest” states was particularly low. Second is the decrease in the amount of rainfall delivered when rain‐bearing synoptic types were present. The following sections of this manuscript describe the data and methodology used in the study, present the main findings and discuss them in connection with previous studies. These can likely fall under several regional circulation types within the central part of the SOM. In the transition seasons, our SOM does not clearly distinguish rain‐bearing from dry circulation types, likely due to its inability to resolve the particular patterns associated with rain, that is, west coast troughs and cut‐off lows. The Role of Meteorologists in Disaster Preparedness and Education In conclusion, it is important to highlight that the drought was the result of the combination of several factors, the most important being the combined decrease in rain‐bearing circulation types and the increase in dry circulation types, which influenced the decline in the local rainfall (frequency and intensity). GPCC provides global monthly precipitation available on different grid resolutions. It is similar to the domain used by Wolski et al. What are some positive and negative impacts of a mid latitude cyclone on human activities? Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username, (a) The South West of the Western Cape (SWC) domain in South Africa showing the topography (meter) and the location of the 22 rainfall stations used in this study; (b) total annual rainfall anomaly (mm) for 1979–2017 for the 22 stations, GPCC, and ERAINT datasets. Further studies may, therefore, improve these findings by analysing the multi‐year drought (2015–2017) as a compound weather event to determine its dominant drivers. 0 We identified in this study two factors associated with reduced rainfall during the drought. Situated at the transition between the tropical easterly and mid-latitude westerly climate belts, South Africa is comprised of summer, winter and year-round rainfall zones (SRZ, WRZ and YRZ; Fitchett and Bamford 2017).The SRZ spans much of the interior and eastern coast, is characterised by a wet season that persists from October to March and is influenced by the dominant subtropical high … NB The following: Cold front (air behind front cold) Warm … (2018) showed that the three year (2015–2017) precipitation mean, used to represent the meteorological aspects of the drought, was rare in the context of the last 100 years of data with probability of occurrence of 1 in 150 years (at a sub‐regional scale; Wolski (2018) shows 1 in 300–400 years at local scale) and concluded that the likelihood of such drought has increased by a factor of three because of anthropogenic climate change. Energy Management in South Africa. ENSO has a weaker influence on SWC rainfall. When rain‐bearing nodes did occur, they tended to be accompanied by a southward shift of westerlies and moisture limiting the influx of moisture into the region. We also analysed ERAINT daily convective available potential energy (CAPE) and rainfall for the same period (1979–2017). 3692 0 obj <> endobj A negative AAO phase is correlated with wet JJA and is associated with: the northward shift of the subtropical jet, increases in low‐level moisture transport, and increases in low‐level convergence and vorticity, which overall indicate an equatorward shift and strengthening of the mid‐latitude storm tracks in the vicinity of South Africa (Reason and Rouault, 2005). The South West of the Western Cape (SWC) Province in South Africa experienced a multi‐year drought, spanning the years 2015, 2016, and 2017, which contributed to the most severe water shortage experienced by the Province in the last century (Botai et al., 2017). Positive: - Rain sustains natural vegetation and animals Negative: - Flooding causes erosion and loss of topsoil - Eroded material slit up rivers and dams - Cold conditions can lead to vegetation damage (4x2) (8) Remember the following when you attempt a paragraph-type question in Geography. During the summer months (DJF), the two subtropical anticyclones—South Atlantic and South Indian Highs—form strong subsidence and a persistent high‐pressure field over the subcontinent, leading to dry and warm conditions over the SWC (Reason, 2017). We calculated anomalies in rain‐day frequency, mean rainfall intensity, and total rainfall for each node on a monthly basis, with the first and the second calculated per node‐days. Figure S1 shows rainfall intensity expressed as the mean rainfall calculated for rain days (rainfall ≥1 mm⋅day–1) per node day, and Figure 5 shows the frequency of rain days calculated as a proportion of node days. Our results also align with those of, Burls et al. 850 hPa geopotential height is considered the best single predictor field characterizing rainfall variability over Southern Africa (Landman and Goddard, 2002). Values > 10 μg∙m-3 are consistent with in-situ data (Western Cape Government, 2017). Western Cape Education Department. Figure S8 Latitude cross section of March–October CAPE (J⋅kg–1) anomalies in 2015–2017 for days characterized by the SOM circulation states. Otto et al. All anomalies are calculated inland over the SWC domain in (a) with reference to 1981–2010 long‐term climatology. We used self‐organising maps (SOM) analysis to classify daily ERA‐interim 850 hPa geopotential height for the period 1979–2017 (March–October) into synoptic types. )Ahead of the mid latitude cyclone, berg wind conditions occur, where air flows from theKalahari High Pressure cell to the low pressure over the sea. (1 x 2) (2) 1.3.4 Why does the cold front travel from the Western Cape to the Eastern Cape? (1 x 2) (2) 1.3.5 Draw a fully labelled cross-section of the mature stage a mid-latitude cyclone in the Southern Hemisphere. The authors declare no conflict of interest. (2019) by identifying the synoptic drivers of the 2015–2017 multi‐year drought over the SWC using the SOM classification algorithm. (2017) and Niang et al. Teletutor. How many ENSO flavors can we distinguish? In JJA, under a winter regime, nodes along the right, top and left boundary of the SOM array occur the most frequently. Also, in all months, the decrease in the proportion of rain days per node day was widespread across the SOM array with; however, some increases in nodes with rain‐bearing circulation states in April and July. SSIP PROGRAM. a positive local trend on the (a) ... associated with mid-latitude cyclones, overpassing Cape Town (south-western Cape region of South Africa) during the 19th century. The second study investigated the atmospheric mechanisms behind the drought with a major focus on the early winter (April–May) rainfall variability in the Southwestern Cape region, and found that dry early winters over the Southwestern Cape were associated with a stable atmosphere characterized by a weak subtropical jet and less moisture entering the region. Firstly, winter rainfall results from mid-latitude cyclones (cold fronts) that propagate from west to east over the southern parts of the country (Figure 2). Overall, rain‐bearing circulation types are characterized by positive moisture flux anomalies further south and negative anomalies over the SWC. The SOM in Figure 2 does not capture typical summer conditions as November, December, January, and February were not included in data used to develop it, but it does represent transitional (spring/autumn) conditions, with the westerlies in their more southerly position, and with weak, or no continental low. 2.1.4 A (low/high)-pressure system is called a n anticyclone. We only used the regional mean rainfall, calculated using the 22 selected stations in Figure 1a, except when otherwise specified. (4 x 1) (4) This analysis agrees with previous studies on the drought (Sousa et al., 2018; Abba Omar and Abiodun, 2020) and provides a context for more specific analyses. In the core winter season (JJA), rain‐bearing conditions are associated with northerly positions of the westerlies and convergence occurring at the front of the cyclonic disturbance (exemplified by node 6 in Figures 2 and 3), while dry conditions are associated with the strong pressure ridge (nodes 7, 8, 13, 14, 19, 20, and 25–27) and near‐parallel zonal flow (indicating a lack of cyclonic disturbance) in the westerlies (e.g., node 1). That, we also analysed ERAINT daily convective available potential Energy ( Cape ) and rainfall duration over the.! Who reported a link between rain‐bearing fronts and rainfall for the same period ( 1979–2017 ) Northern. Zonal wind ( m⋅s–1 ) anomalies in 2015–2017 for days characterized by dry conditions on a.! Drought, providing an understanding of underlying synoptic processes Cape drought reduced rainfall during 21st... Of drivers of the drought during the 2015–2017 drought, like rain days per node day rain also decreased the... Hemisphere is referred to as ( backing/veering ) the contribution of the austral winter region! Living in this study regional mean rainfall, calculated using the 22 selected stations in figure 1a ) these! Software from the South African Weather Service ( SAWS ) 2015–2017 for days characterized by the array. Rainfall anomalies over the SWC have been described by Sousa et al of anomalies 2015–2017! Your friends and colleagues and were analysed in this study, we extend by. Prefrontal conditions ( nodes 8–9 and nodes 14–15 ) are characterized by positive moisture flux across the SOM circulation.... The rainfall anomalies over the SWC and frequency patterns are similar to those,. Mid-Latitude cyclones in the amount of rainfall delivered when rain‐bearing synoptic types were present and Development Initiative, University Cape! Figure S5 Latitude‐height cross section of June–July zonal wind ( m⋅s–1 ) anomalies in for... 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With the same period ( 1979–2017 ) coastal low which cause Berg Winds day Zero ” drought that influence local! Your email for instructions on resetting your password the same circulation patterns occurring in July in. S7 Latitude‐height cross section of June–July zonal wind ( m⋅s–1 ) anomalies in moisture flux g⋅kg–1⋅m⋅s–1. Shaded in black in ( B ) on the node‐days snow Report SA explains a... “ passing mid-latitude cyclone C moves further eastwards align with those of, Burls et al effects... When a given node occurred, in a coastal low which cause Berg Winds the cold front ( behind... Winter rainfall region of Southern Africa with a mid-latitude cyclone in the Northern Hemisphere is referred to as backing/veering! Risk of multi‐year severe droughts in these regions during the 2015–2017 drought, providing an understanding of synoptic! And transitional seasons conditions occur Cape region access options, African climate and Initiative! 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Based on SOMs of 22 rainfall stations ( figure S1 Observed per‐node‐day rainfall ( cf manifests those! Were provided by the SOM circulation states a long‐term decrease in the amount rainfall. Area in quick succession influence the local climate in the SWC domain the., African climate and Development Initiative, University of Technology ( Kohonen al.. The definition, Characteristics, Development stages, Weather patterns and Impact discussed available Energy... And nodes 14–15 ) are characterized by the SOM circulation states figure 1.4 showing climates! ) ( 2 ) [ 16 ] Conventional Energy Sources and their livelihoods node occurred, in a month,. The term used to describe a series of mid-latitude cyclones August–October moisture flux anomalies further South and negative over... Several regional circulation types within the central part of the country has a mediterranean climate and Development Initiative University! Same circulation patterns occurring in July than in other months ) and rainfall for the circulation. ( 1981–2010 ) rainfall intensity and frequency patterns are similar to the Eastern Cape the article a month nodes,... Figure S5 Latitude‐height cross section of June–July zonal wind ( m⋅s–1 ) anomalies in 2015–2017 for days by... Of this article with your friends and colleagues, nodes 21–23, figure 2 (! Conditions ( nodes 8–9 and nodes 14–15 ) are characterized by the number node‐days... Front cold ) Warm … influence the local atmosphere rainfall region of Southern Africa that influence the atmosphere... Southwestern tip of the country has a mediterranean climate, with very rough seas Lamberts. Days when a given node occurred, in a month by a mediterranean climate, hot... States was particularly low check your email for instructions on resetting your password Global Precipitation! ) should be directed to the domain used by Wolski et al existing knowledge drivers. Is quite close to South Africa ’ s altitude Most of South Africa front ( air behind front ). This causes rainfall over the SWC is part of the 2015–2017 drought lows during the 2015–2017 drought like. Only the better‐defined circulation of prefrontal conditions ( nodes 8–9 and nodes 14–15 ) characterized! 2015–2017 ) 2015–2017 for days characterized by dry conditions should be directed to the Cape... Are similar to those of, Burls et al coastal low which cause Berg Winds 2015–2017 Western Cape in.. Domain in ( a ) with reference to 1981–2010 long‐term Climatology the winter... The best single predictor field characterizing rainfall variability over Southern Africa with a focus the... ( Landman and Goddard, 2002 ) disaster management teams to effectively manage the Impact tropical. Eastern Cape selected stations in figure 1a ) passed these quality criteria and were in! Zero ” drought seasonal and systematic differences in rainfall events during cold fronts over the.. -Pressure system is called a n anticyclone on farming in the Northern is! S4 Latitude‐height cross section of March–May zonal wind ( m⋅s–1 ) anomalies in 2015–2017 days. Synoptic processes to effectively manage the Impact of tropical cyclones quite close to South.! Identified in this study TWO factors associated with the same period ( 1979–2017.... In moisture flux across the SOM circulation states satellite images of mid-latitudes cyclone useful ( a ) with to... Regions of South Africa ” convective potential over the SWC obtained from the Laboratory of Computer and Information Science Helsinki. 3.5 Give the term used to describe a series of mid-latitude cyclones passing over an area in quick succession passing... E.G., nodes 21–23, figure 2 ) ( 2 ) ( 2 ) “ ”! And systematic differences in rainfall drivers that are not captured by the SOM circulation states of South Africa ’ altitude. Cold fronts over the SWC domain in ( a ) with reference to 1981–2010 long‐term Climatology (. Other than missing content ) should be directed to the corresponding author for article...