Dry spell frequencies and their variability over southern Africa

Usman, Muhammad; Reason, C. J. C.

doi:10.3354/cr026199

Cited by 203 publications

(171 citation statements)

References 32 publications

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“…Future rainfall scenarios, however, are rather uncertain in this region due to the complexity of the physical mechanisms responsible for Sahelian rainfall patterns (Christensen et al, 2007;Giannini et al, 2008). Furthermore, Usman and Reason (2004) analysed a longer time-series and showed that the most significant increases in occurrences of heavy rainfall events were observed in central Namibia and Angola in the west. Our study indicates that this trend continued from 2001 until 2010.…”

Section: Rainfall Patternsmentioning

confidence: 99%

A conceptual model for assessing rainfall and vegetation trends in sub‐Saharan Africa from satellite data

Hościło

Balzter

Bartholomé³

et al. 2014

Int. J. Climatol

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Policymakers, governments and aid agencies require operational environmental monitoring in support of evidence-based policy-making and resource deployment in crisis situations. For Africa, this is only feasible at sub-continental scale with a large network of automated meteorological stations, a large number of highly coordinated field observers or with satellite remote sensing. The challenge with satellite data lies in the derivation of meaningful environmental indicators. This article describes a conceptual framework for understanding satellite-derived indicators of rainfall and vegetation greenness trends over Africa. It attributes observed vegetation changes to climatic (i.e. rainfall linked) and non-climatic drivers. A decade of annual rainfall and vegetation data over sub-Saharan Africa was analysed using satellite-based rainfall estimates [Famine Early Warning System Rainfall Estimation 2.0 (FEWSNET RFE 2.0)] from National Oceanic and Atmospheric Administration's (NOAA's) Climate Prediction Centre and the Normalized Difference Vegetation Index (NDVI) obtained from the Satellite Pour l'Observation de la Terre Vegetation (SPOT-VGT) sensor. Rainfall and vegetation greenness trends were analysed for 759 administrative regions of sub-Saharan Africa to identify those regions that have experienced a negative, positive or stable rainfall/vegetation trend over the period [2001][2002][2003][2004][2005][2006][2007][2008][2009][2010]. The character of the relationship between the annual rainfall and max NDVI trends were examined to identify areas where the changes in greenness could be attributed to climatic (rainfall) and non-climatic (human land use or ecological disturbance) changes. Regions where increasing rainfall was associated with vegetation greening were found in West Africa, Central African Republic, West Cameroon and northeastern part of South Africa, whereas areas with evidence of 'climatic vegetation degradation' were located in Southern Madagascar, Nigeria, Kenya and the Garden Route region of South Africa.

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Section: Rainfall Patternsmentioning

confidence: 99%

A conceptual model for assessing rainfall and vegetation trends in sub‐Saharan Africa from satellite data

Hościło

Balzter

Bartholomé³

et al. 2014

Int. J. Climatol

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“…For agricultural practices, the consistency with which the basic minimum of needed rainfall is received is more important than the total received over time. Crops are more likely to do well with uniformly spread 'light' rains than with a few 'heavy' rains interrupted by dry periods (Usman and Reason, 2004;Hachigonta and Reason, 2006). The timing of rainfall onset, duration, and cessation relative to the cropping calendar is more fundamental to crop viability than focusing on total seasonal rainfall alone.…”

Section: Introductionmentioning

confidence: 99%

Intra‐seasonal variability over the northeastern highlands of Tanzania

Kijazi

Reason

2011

Intl Journal of Climatology

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ABSTRACT:The intra-seasonal variability of rainfall over the northeastern Highlands (NEH) of Tanzania during the March, April, May (MAM) rainfall season and associated circulation anomalies have been studied for selected wet and dry years. Station rainfall data were used to extract the onset, peak, and cessation dates of the rainfall season and National Center for Atmospheric Research/National Center for Environmental Prediction (NCEP/NCAR) data were used to study the atmospheric circulation features associated with the intra-seasonal variability. It was found that the anomalously wet MAM seasons over the NEH of Tanzania tend to result from an earlier onset of the rains and a late cessation and thus, a longer-than-average rainfall season, whereas, dry years were characterized by a shorter-than-average duration of the rains. The moisture flux plots indicate that the composite wet MAM seasons were associated with advection of moisture from both the Indian Ocean and the Congo Basin. For the dry MAM seasons, a cyclonic anomaly off the Somali coast leads to southerly moisture flux anomalies over Kenya and westerly anomalies over the Indian Ocean which, together with easterly moisture flux anomalies over the Congo Basin, act to divert and transport low-level moisture away from Tanzania.Lag correlations between time series of moisture over the Congo (0-8°S; 20-29°E) and MAM rainfall over the NEH indicated a phase locking of the two variables that occurred during the years with larger rainfall anomalies. A significant correlation was observed two months before the onset of the rainfall season in January that indicates that some predictability of the MAM seasonal rainfall total based on the Congo Basin zonal wind may exist. However, given the constraints of the available data and the regional atmospheric circulation, it is possible that additional predictors may be required when developing forecast models of the MAM seasonal rainfall.

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“…Effects of CA on infiltration and soil water Rainfall distribution patterns during the growing season in Southern Africa are characterized by mid-season dry spells 63,64 . Thus, higher infiltration rates under CA and surface crop residue retention have the potential to buffer growing crops against intermittent periods of drought stress.…”

Section: Conservation Agriculture In Southern Africamentioning

confidence: 99%

Conservation agriculture in Southern Africa: Advances in knowledge

Thierfelder¹,

Rusinamhodzi²,

Ngwira

et al. 2014

Renew. Agric. Food Syst.

140

112

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The increasing demand for food from limited available land, in light of declining soil fertility and future threats of climate variability and change have increased the need for more sustainable crop management systems. Conservation agriculture (CA) is based on the three principles of minimum soil disturbance, surface crop residue retention and crop rotations, and is one of the available options. In Southern Africa, CA has been intensively promoted for more than a decade to combat declining soil fertility and to stabilize crop yields. The objective of this review is to summarize recent advances in knowledge about the benefits of CA and highlight constraints to its widespread adoption within Southern Africa. Research results from Southern Africa showed that CA generally increased water infiltration, reduced soil erosion and run-off, thereby increasing available soil moisture and deeper drainage. Physical, chemical and biological soil parameters were also improved under CA in the medium to long term. CA increased crop productivity and also reduced on-farm labor, especially when direct seeding techniques and herbicides were used. As with other cropping systems, CA has constraints at both the field and farm level. Challenges to adoption in Southern Africa include the retention of sufficient crop residues, crop rotations, weed control, pest and diseases, farmer perception and economic limitations, including poorly developed markets. It was concluded that CA is not a 'one-size-fits-all' solution and often needs significant adaptation and flexibility when implementing it across farming systems. However, CA may potentially reduce future soil fertility decline, the effects of seasonal dry-spells and may have a large impact on food security and farmers' livelihoods if the challenges can be overcome.

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Dry spell frequencies and their variability over southern Africa

Cited by 203 publications

References 32 publications

A conceptual model for assessing rainfall and vegetation trends in sub‐Saharan Africa from satellite data

A conceptual model for assessing rainfall and vegetation trends in sub‐Saharan Africa from satellite data

Intra‐seasonal variability over the northeastern highlands of Tanzania

Conservation agriculture in Southern Africa: Advances in knowledge

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