scholarly journals Changes in Rainfall in Sierra Leone: 1981–2018

Climate ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 144 ◽  
Author(s):  
Richard Wadsworth ◽  
Amie Jalloh ◽  
Aiah Lebbie
Keyword(s):  
Sierra Leone ◽  
Extreme Events ◽  
Rainy Season ◽  
West African Monsoon ◽  
Agricultural Practices ◽  
West African ◽  
Annual Rainfall ◽  
The West ◽  
Daily Data ◽  
Objective Evidence

Sierra Leone on the west coast of Africa has a monsoon-type climate. Reports by politically influential donors regularly state that Sierra Leone is extremely vulnerable to climate change, but the objective evidence backing these statements is often unreported. Predicting the future climate depends on modelling the West African monsoon; unfortunately, current models give conflicting results. Instead, changes in rainfall over the last four decades are examined to see if there are already significant changes. Rainfall records are extremely limited, so the Climate Hazards Group InfraRed Precipitation with Station daily data at a spatial resolution of 0.05 degrees was used. In addition to total annual rainfall, the characteristics of the early rainy season (critical for farmers), the length of the rainy season and growing season, and the frequency of extreme events were calculated. There is evidence for a significant reduction in annual rainfall in the northwest. There is only limited support for the widely held belief that the start of the rainy season is becoming more erratic and that extreme events are becoming more common. El-Niño was significant in the southeast. If these trends continue, they will exacerbate the consequences of temperature increases (predicted to be between 1 and 2.6 °C by 2060) and negatively affect the livelihoods and agricultural practices of the rural poor.

scholarly journals Integration of Weather System Variability to Multidecadal Regional Climate Change: The West African Sudan–Sahel Zone, 1951–98

2006 ◽  
Vol 19 (20) ◽  
pp. 5343-5365 ◽  
Author(s):  
Michael A. Bell ◽  
Peter J. Lamb
Keyword(s):  
Rainy Season ◽  
Regional Climate ◽  
West African ◽  
Seasonal Rainfall ◽  
Annual Rainfall ◽  
Large Set ◽  
The West ◽  
Weather System ◽  
Linear Type ◽  
System Variability

Abstract Since the late 1960s, the West African Sudan–Sahel zone (10°–18°N) has experienced persistent and often severe drought, which is among the most undisputed and largest regional climate changes in the last half-century. Previous documentation of the drought generally has used monthly, seasonal, and annual rainfall totals and departures, in a standard “climate” approach that overlooks the underlying weather system variability. Most Sudan–Sahel rainfall occurs during June–September and is delivered by westward-propagating, linear-type, mesoscale convective systems [disturbance lines (DLs)] that typically have much longer north–south (102–103 km) than east–west (10–102 km) dimensions. Here, a large set of daily rainfall data is analyzed to relate DL and regional climate variability on intraseasonal-to-multidecadal time scales for 1951–98. Rain gauge–based indices of DL frequency, size, and intensity are evaluated on a daily basis for four 440-km square “catchments” that extend across most of the West African Sudan–Sahel (18°W–4°E) and are then distilled into 1951–98 time series of 10-day and seasonal frequency/magnitude summary statistics. This approach is validated using Tropical Applications of Meteorology Using Satellite Data (TAMSAT) satellite IR cold cloud duration statistics for the same 1995–98 DLs. Results obtained for all four catchments are remarkably similar on each time scale. Long-term (1951–98) average DL size/organization increases monotonically from early June to late August and then decreases strongly during September. In contrast, average DL intensity maximizes 10–30 days earlier than DL size/organization and is distributed more symmetrically within the rainy season for all catchments except the westernmost, where DL intensity tracks DL size/organization very closely. Intraseasonal and interannual DL variability is documented using sets of very deficient (8) and much more abundant (7) rainy seasons during 1951–98. The predominant mode of rainfall extremes involves near-season-long suppression or enhancement of the seasonal cycles of DL size/organization and intensity, especially during the late July–late August rainy season peak. Other extreme seasons result solely from peak season anomalies. On the multidecadal scale, the dramatic decline in seasonal rainfall totals from the early 1950s to the mid-1980s is shown to result from pronounced downtrends in DL size/organization and intensity. Surprisingly, this DL shrinking–fragmentation–weakening is not accompanied by increases in catchment rainless days (i.e., total DL absence). Like the seasonal rainfall totals, DL size/organization and intensity increase slightly after the mid-1980s.

scholarly journals The effect of explicit convection on climate change in the West African monsoon and central West African Sahel rainfall

2021 ◽  
pp. 1-42
Keyword(s):  
Climate Change ◽  
West African Monsoon ◽  
West African ◽  
Annual Rainfall ◽  
Moist Convection ◽  
The West ◽  
African Monsoon ◽  
Dominant Feature ◽  
West African Sahel ◽  
African Sahel

Abstract The West African monsoon (WAM) is the dominant feature of West African climate providing the majority of annual rainfall. Projections of future rainfall over the West African Sahel are deeply uncertain with a key reason likely to be moist convection, which is typically parameterized in global climate models. Here, we use a pan-Africa convection permitting simulation (CP4), alongside a parameterized convection simulation (P25), to determine the key processes that underpin the effect of explicit convection on the climate change of the central West African Sahel (8°W-2°E, 12-17°N). In current climate, CP4 affects WAM processes on multiple scales compared to P25. There are differences in the diurnal cycles of rainfall, moisture convergence, and atmospheric humidity. There are upscale impacts: the WAM penetrates farther north, there is greater humidity over the north Sahel and the Saharan heat low regions, the sub-tropical subsidence rate over the Sahara is weaker, and ascent within the tropical rain belt is deeper. Under climate change, the WAM shifts northwards and Hadley circulation weakens in P25 and CP4. The differences between P25 and CP4 persist, however, underpinned by process differences at the diurnal and large-scales. Mean rainfall increases 17.1% in CP4 compared to 6.7% in P25 and there is greater weakening in tropical ascent and sub-tropical subsidence in CP4. These findings show the limitations of parameterized convection and demonstrate the value that explicit convection simulations can provide to climate modellers and climate policy decision makers.

Development and Operation of Ebola Diagnostic Laboratories Led By Public Health England in Sierra Leone during the West African Ebola Outbreak 2013-2015

2016 ◽  
Vol 1 (4) ◽  
Author(s):  
Daniel Bailey ◽  
Jane Shallcross ◽  
Christopher H. Logue ◽  
Simon A. Weller ◽  
Liz Evans ◽  
...  
Keyword(s):  
Public Health ◽  
Sierra Leone ◽  
West African ◽  
The West

scholarly journals On What Scale Can We Predict the Agronomic Onset of the West African Monsoon?

2016 ◽  
Vol 144 (4) ◽  
pp. 1571-1589 ◽  
Author(s):  
Rory G. J. Fitzpatrick ◽  
Caroline L. Bain ◽  
Peter Knippertz ◽  
John H. Marsham ◽  
Douglas J. Parker
Keyword(s):  
West Africa ◽  
Noise Analysis ◽  
West African Monsoon ◽  
West African ◽  
New Method ◽  
The West ◽  
African Monsoon ◽  
Spatial Consistency ◽  
Local Stakeholders ◽  
Local Rainfall

Abstract Accurate prediction of the commencement of local rainfall over West Africa can provide vital information for local stakeholders and regional planners. However, in comparison with analysis of the regional onset of the West African monsoon, the spatial variability of the local monsoon onset has not been extensively explored. One of the main reasons behind the lack of local onset forecast analysis is the spatial noisiness of local rainfall. A new method that evaluates the spatial scale at which local onsets are coherent across West Africa is presented. This new method can be thought of as analogous to a regional signal against local noise analysis of onset. This method highlights regions where local onsets exhibit a quantifiable degree of spatial consistency (denoted local onset regions or LORs). It is found that local onsets exhibit a useful amount of spatial agreement, with LORs apparent across the entire studied domain; this is in contrast to previously found results. Identifying local onset regions and understanding their variability can provide important insight into the spatial limit of monsoon predictability. While local onset regions can be found over West Africa, their size is much smaller than the scale found for seasonal rainfall homogeneity. A potential use of local onset regions is presented that shows the link between the annual intertropical front progression and local agronomic onset.

scholarly journals A Lagrangian perspective on stable water isotopes during the West African Monsoon

2021 ◽  
Author(s):  
Christopher Johannes Diekmann ◽  
Matthias Schneider ◽  
Peter Knippertz ◽  
Andries Jan de Vries ◽  
Stephan Pfahl ◽  
...  
Keyword(s):  
West African Monsoon ◽  
West African ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
The West ◽  
African Monsoon

A hydrological onset and withdrawal index for the West African monsoon

2008 ◽  
Vol 96 (1-2) ◽  
pp. 179-189 ◽  
Author(s):  
G. A. Dalu ◽  
M. Gaetani ◽  
M. Baldi
Keyword(s):  
West African Monsoon ◽  
West African ◽  
The West ◽  
African Monsoon

English in West Africa

2015 ◽  
Author(s):  
Ulrike Gut
Keyword(s):  
West Africa ◽  
Sierra Leone ◽  
Structural Properties ◽  
West African ◽  
The Other ◽  
African Countries ◽  
The West ◽  
Current Role ◽  
British Colonization

This chapter describes the history, role, and structural properties of English in the West African countries the Gambia, Sierra Leone, Liberia, Ghana, Nigeria, the anglophone part of Cameroon, and the island of Saint Helena. It provides an overview of the historical phases of trading contact, British colonization and missionary activities and describes the current role of English in these multilingual countries. Further, it outlines the commonalities and differences in the vocabulary, phonology, morphology, and syntax of the varieties of English spoken in anglophone West Africa. It shows that Liberian Settler English and Saint Helenian English have distinct phonological and morphosyntactic features compared to the other West African Englishes. While some phonological areal features shared by several West African Englishes can be identified, an areal profile does not seem to exist on the level of morphosyntax.

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