Tropical woodlands and forests had all but disappeared, existing only in mountain refuges (Nicholson & Flohn, 1980). Communicating climate change forecasts in clinical numbers is one of the reasons people may not fully appreciate the threat to our collective wellbeing as increasing temperatures and extreme weather events become more likely with the worlds climate continuing to shift away from historic trends. Figure 4. Links between the climate crisis and migration are intensifying in West Africa, where many people work in sectors vulnerable to climate-related extremes of weather and sea level rise. What to Pack: If you're going on safari, your packing list should include T-shirts, trousers, cotton underwear, sports bras, sunglasses, and a wide-brimmed hat. These are often sandy on the surface with clay layers below, so drainage can be poor. This effectively decouples the ITCZ from the region of significant rainfall. rain Weather West Africa, Satellite Weather West Africa, Weather Forecast, Rainfall, Clouds, Sun in West Africa - Source: SAT24.com This facilitates the development of precipitation within the deep meridional cell and near the coast, but little rainfall is associated with the convergence within the shallow meridional cell. In such cases, westerlies can prevail up to the mid-troposphere, in which case they display the AEJ poleward. Found inside Page 1991 Africa and the south west Indian Ocean . Climate Dyn . , 15 , 937-951 . Tyson , P. D. , and R. A. Preston - Whyte , 2000 : The Weather and Climate of During the transition season months of April and October, high pressure prevails over the Sahara and the northeast Harmattan is the dominant flow, as it is in January. Oxford Research Encyclopedia of Climate Science, Climate Impact: Managed Ecosystems and Agriculture, Climate Systems and Climate Dynamics: Biogeochemistry, Climate Systems and Climate Dynamics: Theoretical Foundations, Rainfall Conditions from Historical to Modern Times, A Conceptual Model of Rainfall Variability Over the Sahel, Large-Scale Forcing of Rainfall Variability in the Sahel, https://doi.org/10.1093/acrefore/9780190228620.013.510, Conceptual Model of Rainfall Variability over the Sahel, The impact of decadal-scale Indian Ocean sea surface temperature anomalies on Sahelian rainfall and the North Atlantic Oscillation, Seasonal cycle and interannual variability of the Sahelian rainfall at hydrological scales, Tropical SST and Sahel rainfall: A non-stationary relationship, Changes in the interannual SST-forced signals on West African rainfall: AGCM intercomparison, The West African Sahel: A review of recent studies on the rainfall regime and its interannual variability, Monsoon onset over Sudan-Sahel: Simulation by a regional scale model MM5, Robust features of Atlantic multi-decadal variability and its climate impacts, Climate of Western and Central Equatorial Africa. The desert surface is composed primarily of regs, which are stone pavements covering about 68% of the Sahara (LeHouerou, 1986). The southwest stays cold and wet well into spring, typical of its Mediterranean climate. A widespread example of this is the so-called brousse tigre (tiger bush, Figure 6), a notable Sahelian feature (Nicholson, 1995). During the transitional phase, which occurs in early July, a decrease in rainfall is observed and the peak rainfall occurs around 6 N. Lebel et al. Starting in September, temperatures usually climb above 60 degrees Fahrenheit (16 degrees Celsius) in Cape Town and to almost 80 degrees Fahrenheit (27 degrees Celsius) in Pretoria. Those along the northerly track (1820 N) are seldom associated with precipitation. Light/dark shading indicates below/above normal rainfall. After all, if todays maximum temperature is 25C, and tomorrows is 27C, thats pretty manageable, right? This dramatically reduces visibility and poses a health hazard. Daily high temperatures rarely exceed 84 degrees Fahrenheit (29 degrees Celsius), and rainy seasons span March to May and October through November. This volume provides an up to date overview of climate variability during the 20th century in the context of natural and anthropogenic variability. These are evident on both modern and historical time scales (Nicholson, 2014). The remote factors regulating the regional circulation are less well understood. An overall more humid climate probably persisted well into the 1700s, but commencing in the mid-1600s a series of disastrous droughts occurred. In unimodal regions maximum rainfall occurs on average in August. Climate is a long-term weather pattern, the sum of features such as temperature, rainfall, and wind. Today the region is home to major cities such as Dakar (Senegal), Niamey (Niger), Bamako (Mali), and Khartoum (Sudan), but most of the inhabitants live in rural areas and practice agriculture. In addition to such transient storms, a dust haze often persists near the surface for weeks at a time, especially during the boreal winter. Figure 17. On a mission: Evangelicals flock to the Amazon home of isolated tribes, Conservation summit opens amid debate over role of indigenous people, Waiting for Cop26 vaccines Climate Weekly, New York floods show subway systems must be prepared for climate change, Frustration mounts as Cop26 delegates wait for the UKs promised Covid vaccines. Over the Sahel the contribution to total rainfall ranges from less than 20% in the south to more than 80% in the north (Jackson, Nicholson, & Klotter, 2009). In Liberia, the climate is tropical, hot and humid all year round, with a rainy season from May to October due to the African monsoon, and pretty frequent rains in the other months, except in the short dry season that runs from December to February, which is more marked in the north. Equatorial West and Central Africa havea monsoon climate defined by high temperatures, soaring humidity, and heavy seasonal rains. In the case of the dipole, Nicholson and Webster (2007) demonstrated that the wet Sahel/dry Guinea coast pattern is linked to inertial instability. The bottom diagram gives mean August rainfall (mm mo1, averaged for 10 W to 10 E) as a function of latitude, with the location of the Sahel indicated on the latitudinal axis. Along the coast, the rainfall exceeds 3,000 millimeters (118 inches) per year. Strictly speaking, there are no 'seasons' as such, as temperatures don't vary a great deal throughout the year. A unique feature of Sahel climate is that is rainfall regime is perhaps the most sensitive in the world and this sensitivity is apparent on all of these time scales. Cloud cover in the humid zone tends to range from 50% in the driest months to 80100% during the wet season. This is as the region warms and the monsoon rains are disrupted in response to worsening global atmospheric carbon pollution. The current image of the monsoon contrasts with the classic picture of West African climate in the diminished importance of the ITCZ and the inclusion of several jet streams and the Saharan Heat Low. The diurnal and annual range of temperature (Figure 13) are also strongly influenced by latitude, but aridity and proximity to the ocean also play a role. Its direction is northeasterly when embedded within the Harmattan but southwesterly when embedded within the monsoon flow. Peoples sleep patterns are often disrupted during heatwaves, particularly for those who dont have air conditioning in their homes. This may be a result of the strong relationship between the cross-equatorial pressure gradient and Sahel rainfall, as described in section on a Conceptual Model of Rainfall Variability over the Sahel. The AMO and this pressure gradient over West Africa are closely linked (Nicholson & Webster, 2007). This publication, prepared jointly by the WHO, the World Meteorological Organization and the United Nations Environment Programme, considers the public health challenges arising from global climate change and options for policy responses, The monsoon also includes three areas of convergence and two meridionally (north-south) oriented vertical circulation cells. Figure 15 presents vertical cross-sections of the mean zonal wind over West Africa in these same four months. For one, these tend to roughly follow the rainfall seasonality. The spatial coherence is strong enough that two spatial modes of variability prevail. A shallow meridional cell is centered over and driven by the Saharan Heat Low and also corresponds to the surface position of the ITCZ. Within the semi-arid zones, rainfall systematically shifts from 50 mm/year with a rainy season lasting 12 months, to 1,000 mm/year with a rainy season lasting 35 months. Afternoon relative humidity is more typically on the order of 6070%. The climate is tropical and humid with a wet and a dry season. Exceptions are areas along the Atlantic coast, where it is as low as 912 C, and the highlands of the Sudan, where it exceeds 22 C. In July the diurnal range varies from 68 C in the lowest latitudes to 15 C in the northern Sahel. Within some 1,000 km, the environment transitions from the hyper-arid Sahara Desert to forests with over 1,200 mm of rainfall per year. He speculated that albedo changes linked to overgrazing modified the radiation balance in such a way that increased subsidence was required to produce a radiative equilibrium. These are the most widespread soils, covering some 50% of the northern Sahel and roughly a quarter of the Sahel overall (FAO, 1991). In 1919 Debundscha received nearly 15,000 mm of rainfall. Climate change is also accelerating migration and displacement in West Africa, especially in the Sahel. Figure 29. Zonation of vegetation and climate in West Africa. (2011) identify four key phases of the annual cycle of the monsoon, distinguished by the location of peak rainfall. The driest season is June through September, making this a prime time for gorilla trekking or other outdoor activities in the country. An MCS is essentially a large, continuous area of deep cloud (at least 2,000 km) in which one or more areas of convective precipitation are embedded. Both include a diagonal trough emanating from the midlatitude westerlies at upper levels toward the tropics (Figure 26). Figure 28. These are collectively termed Mesoscale Convective Systems (MCSs) by some authors, while others (e.g., Nesbitt & Zipser, 2003) reserve this label for cold systems, that is, those in which ice is present in the upper levels of cloud. Based on an International Workshop held in Geneva in 2005, this book reviews the advances made so far in seasonal climate predictions and their applications for management and decision-making in agriculture. Rainfall in the Guinea Coast has recovered to some extent in recent years, but the Sahel rainfall has exceeded the long-term mean in only a handful of years. What does pastoralism have to do with climate change? See oureditorial guidelinesfor what this means. Uganda has a warm tropical climate, with temperatures ranging from 25-29C (77- 84F), apart from in the mountainous areas, which are much cooler; the top of Mount Elgon is often covered with snow. The climate of South Africas west coast region is Easterly waves help to generate dust (Knippertz & Todd, 2010; Jones, Mahowald, & Luo, 2003). The SAL resides between roughly 900 mb/1,800 m and 500 mb/5,500m near the Atlantic coast (Carlson & Prospero, 1972), but it extends considerably higher over the continent (Parker, Thorncroft, Burton, & Diongue-Niang, 2005). One of the most significant aspects of West African, and particularly Sahelian, climate is its extreme variability on time scales ranging from years to millennia. The biggest source is from the Bodl Depression, the site of the expanded Lake Chad some 5,000 years ago. Early work on AEWs emphasized their development from the AEJ via combined barotropic-baroclinic instability and their role in organizing and promoting convection. More detail about the relationship to SSTs can be found in Biasutti, Held, Sobel, and Giannini (2008) and Rodriguez-Fonseca et al. The picture is very different in July when a thermal low exists over the northwestern Sahara, between the Hoggar and the Atlas Mountains. The rainfall associated with them can extend as far south as the Guinea Coast. Most of the rain is associated with a small number very intense storms. Several representations of the monsoon were developed independently by these authors, but they all are substantially similar in their most salient features. This era was actually part of a major, continent-wide period of anomalously dry conditions. A cold tongue develops just south of the equator in the Atlantic. These are the oceanic, coastal, transitional, and Sahelian phases. This article was written byLeonie Joubertas part of a series covering the science produced by various FCFA projects, and introduces some of the people behind it. The African Easterly Jet position is also indicated. These help to maintain the integrity of the layer and its thermal structure and its relatively uniform conditions of high heat content and low moisture content. Explores some of the United States most severe or unusual weather systems, including electrified dust storms, pink snowstorms, luminous tornadoes, ball lightning, and falls of fish and toads.

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