An analysis of recent rainfall conditions in eastern Africa

Nicholson, Sharon E.

doi:10.1002/joc.4358

Cited by 85 publications

(79 citation statements)

References 20 publications

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“…Black et al, 2003;Nicholson, 2016). To cover the interannual variability, three further scenarios were constructed to explore the impact of potentially varying amplitudes of seasonal cycles: a warm amplification (AMPW) in which the wet seasons from WW and the dry seasons from CD are merged, a cold amplification (AMPC) in which the wet seasons from WET and the dry seasons from CD are merged, and an attenuated scenario (ATT) in which the wet seasons from CD are combined with the dry seasons from WW.…”

Section: Sampling Synthetic Climate Scenariosmentioning

confidence: 99%

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

et al. 2016

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Abstract. The Lewis Glacier on Mt. Kenya is one of the best studied tropical glaciers and has experienced considerable retreat since a maximum extent in the late 19th century (L19). From distributed mass and energy balance modelling, this study evaluates the current sensitivity of the surface mass and energy balance to climatic drivers, explores climate conditions under which the L19 maximum extent might have been sustained, and discusses the potential for using the glacier retreat to quantify climate change. Multi-year meteorological measurements at 4828 m provide data for input, optimization, and evaluation of a spatially distributed glacier mass balance model to quantify the exchanges of energy and mass at the glacier-atmosphere interface. Currently the glacier loses mass due to the imbalance between insufficient accumulation and enhanced melt, because radiative energy gains cannot be compensated by turbulent energy sinks. Exchanging model input data with synthetic climate scenarios, which were sampled from the meteorological measurements and account for coupled climatic variable perturbations, reveals that the current mass balance is most sensitive to changes in atmospheric moisture (via its impact on solid precipitation, cloudiness, and surface albedo). Positive mass balances result from scenarios with an increase of annual (seasonal) accumulation of 30 % (100 %), compared to values observed today, without significant changes in air temperature required. Scenarios with lower air temperatures are drier and associated with lower accumulation and increased net radiation due to reduced cloudiness and albedo. If the scenarios currently producing positive mass balances are applied to the L19 extent, negative mass balances are the result, meaning that the conditions required to sustain the glacier in its L19 extent are not reflected in today's meteorological observations using model parameters optimized for the present-day glacier. Alternatively, a balanced mass budget for the L19 extent can be achieved by changing both climate and optimized gradients (used to extrapolate the meteorological measurements over the glacier) in a manner that implies a distinctly different coupling between the glacier's local surface-air layer and its surrounding boundary layer. This result underlines the difficulty of deriving palaeoclimates for larger glacier extents on the basis of modern measurements of small glaciers.

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Section: Sampling Synthetic Climate Scenariosmentioning

confidence: 99%

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

et al. 2016

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“…These studies showed that land surface processes and sea surface temperatures (SST) are the main drivers of droughts over West Africa. The land surface processes include surface albedo (Charney 1975;Charney et al 1977;Abiodun et al 2008), radiative effects of desert dust (Yoshioka et al 2007;Solmon et al 2012;Klüser and HolzerPopp 2010), and changes in surface hydrology (Nicholson et al 2000). Nevertheless, some studies argue that SST forcing plays the major role in West African drought (Hagos and Cook 2008), while land surface forcing only amplifies (or dampens) the changes owing to the SST forcing (Rowell 2001;Hoerling et al 2006;Cook 2008;Fontaine et al 1998;Taylor et al 2002;Giannini et al 2003).…”

Section: Introductionmentioning

confidence: 97%

Drought modes in West Africa and how well CORDEX RCMs simulate them

Diasso

Abiodun

2015

Theor Appl Climatol

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This study presents the spatial-temporal structure of droughts in West Africa and evaluates the capability of CORDEX regional climate models in simulating the droughts. The study characterize droughts with the standardized evapotranspiration index (SPEI) computed using the monthly rainfall and temperature data from the Climatic Research Unit (CRU) and CORDEX models simulation datasets. To obtain the spatial-temporal structure of the droughts, we applied the principal component analysis on the observed and simulated SPEIs and retained the first four principal factors as the leading drought modes over West Africa. The relationship between the drought modes and atmospheric teleconnections was studied using wavelet coherence analysis, while the ability of the CORDEX models to simulate the drought modes was quantified with correlation analysis. The analysis of the relationship between drought modes and atmospheric teleconnections is based on SPEI from observation dataset (CRU). The study shows that about 60 % of spatial-temporal variability in SPEI over West Africa can be grouped into four drought modes. The first drought mode features drought over east Sahel, the second over west Sahel, the third over the Savanna, and the fourth over the Guinea coast. Each drought mode is linked to sea surface temperature anomalies (SSTAs) over tropical areas of Pacific, Atlantic, and Indian Oceans.Most CORDEX models reproduce at least two of the drought modes, but only two models (REMO and CNRM) reproduce all the four drought modes. REMO and WRF give the best simulation of the seasonal variation of the drought mode over the Sahel in March-May and June-August seasons, while CNRM gives the best simulation of seasonal variation in the drought pattern over the Savanna. Results of this study may guide in selecting appropriate CORDEX models for seasonal prediction of droughts and for downscaling projected impacts of global warming on droughts in West Africa.

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“…Also, drought in the region used to be attributed to a simple southward displacement of the Inter-Tropical Convergence Zone (ITCZ) [10]. This rather simplistic explanation has been rejected because it failed to explain many important characteristics of rainfall such as late onset or early cessation [11] [12].…”

Section: Introductionmentioning

confidence: 99%

Trend Analysis of Drought in the Guinea and Sudano-Sahelian Climatic Zones of Northern Nigeria (1907-2006)

Omonijo¹,

Okogbue²

2014

ACS

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A quantitative assessment of drought characteristics and their associated variability in the Northern Nigeria was carried out. Monthly rainfall data for all the selected locations which span a period of 100 years collected from the Climate Research Unit (CRU) database were used. The resolution of the data is 0.5 × 0.5 degrees in longitude and latitude. The long-term rainfall records were analyzed for drought using standardized precipitation index (SPI). The 100 years of Study was subdivided into 10 decades. Using Ilwis GIS software, the SPI results were presented on a spatial digitized map of northern Nigeria. This was done using the coordinates got from the Nigerian Meteorological Agency, Lagos Nigeria. The results of SPI analysis revealed that there were several drought years in the study period. Analysis further revealed that decade 7 to decade 9 (i.e. 1967-1976, 1977-1986, 1987-1996) witnessed persistent drought in the northern Nigeria. These were classified into mild, moderate, severe and extreme drought conditions. Near normal dry or mild drought was predominant in the 100 years of study. Mild drought has the highest number of occurrence in the northern Nigeria. A closer examination shows that north eastern part of Nigeria is susceptible to moderate drought. SPI analysis for 1, 3, 6 and 12 months was carried out. According to the Nigerian Meteorological Agency Classification, 1 month represents meteorological drought, 3 months represents agricultural drought, 6 months represents hydrological drought and 12 months represents socio-economic drought. The SPI analysis revealed distinct period of negative and positive values in which negative values indicate occurrence of drought and positive values imply there is no drought. This study has provided useful information and pro-active intervention to reduce the impact of drought which will be helpful to effectively plan rain-fed agriculture in northern Nigeria.

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An analysis of recent rainfall conditions in eastern Africa

Cited by 85 publications

References 20 publications

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

Drought modes in West Africa and how well CORDEX RCMs simulate them

Trend Analysis of Drought in the Guinea and Sudano-Sahelian Climatic Zones of Northern Nigeria (1907-2006)

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