Desmond Manatsa

Impact of Mascarene High variability on the East African ‘short rains’

The interannual variability of East African ‘short rains’ (EASR) and its link with the Mascarene High (MH) variation are explored, using observations and reanalysis data. Correlation and composite analyses for flood and drought events reveal that the EASR variability is strongly linked to the MH zonal displacement, in particular, the zonal movement of the MH eastern ridge. When the MH eastern ridge is anomalously displaced to the west (east) of its normal position, the south east (SE) trade winds over the South Indian Ocean (SIO) anomalously strengthen (weaken). This enhances (reduces) the relatively cool and dry SE trade winds and induces cold (warm) sea surface temperature anomaly in the SIO. As a result, convection over the western equatorial SIO is suppressed (enhanced) and leads to rainfall deficits (excess) over East Africa. Droughts in East Africa are associated with a westward migration of the MH eastern ridge, while the relationship is less clear for flood events and their link to an eastward migration of the MH. Therefore, the zonal migration of the MH eastern ridge provides a novel indicator for the EASR extremes especially droughts. This revelation has immense social application for rainfall forecast over East Africa where rainfall deficits have become more prevalent against the background of deteriorating conventional forecasts for EASR droughts.

On the Epochal Strengthening in the Relationship between Rainfall of East Africa and IOD

AbstractVariability of the equatorial East Africa “short rains” (EASR) has intensified significantly since the turn of the twentieth century. This increase toward more extreme rainfall events has not been gradual but is strongly characterized by epochs. The rain gauge–based Global Precipitation Climatology Centre (GPCC) monthly precipitation dataset for the period 1901–2009 is used to demonstrate that the epochal changes were dictated by shifts in the Indian Ocean dipole (IOD) mode. These shifts occurred during 1961 and 1997. In the pre-1961 period, there was virtually no significant linear link between the IOD and the EASR. But a relatively strong coupling between the two occurred abruptly in 1961 and was generally maintained at that level until 1997, when another sudden shift to even a greater level occurred. The first principal component (PC1) extracted from the EASR spatial domain initially merely explained about 50% of the rainfall variability before 1961, and then catapulted to about 73% for the per...

Shifts in IOD and their impacts on association with East Africa rainfall

The decadal shift in the relationship between the Indian Ocean Dipole (IOD) and the East African rainfall is investigated using historical observational data. The climate system for equatorial East Africa (EEA) during the October to December (OND) ‘short rains’ season is characterised by spatiotemporal variations of the equatorial East African rainfall (EEAR). Therefore, the EEAR index is derived from the first principal component of the empirical orthogonal function analysis (EOF) of the EEA’s rainfall domain. The IOD, which has been linked with the EEAR in the previous studies, is the main climate mode controlling the tropical Indian Ocean during the OND period. It is usually represented by a dipole mode index based on the zonal gradient of SST anomalies in the tropical Indian Ocean. Therefore the climate modes, IOD and EEAR, are assumed to form a two-node network of subsystems which primarily control the climate of equatorial East Africa during the OND period. The collective behaviour of these climate modes is investigated through the examination of their representative indices for the period 1901 to 2009 using simple statistical techniques. The results suggest that the interaction between these two climate modes, which comprise the network, is not predominantly linear as previously assumed, but is characterised by shifts which are determined by the coupling and synchronisation processes of the tropical systems. In cases where synchronisation is preceded by an abrupt increase in coupling strength between the two subsystems, the established synchronous state is destroyed and a new climate state emerges such as in the years 1961 and 1997. This alteration in the regional climate is accompanied by notable changes in the regional rainfall and IOD variations. But in those events where synchronisation is followed by a sudden loss in coupling strength, the climate state is not disturbed and no shift in the climate of equatorial East Africa is noticed as in 1918. This climate shift mechanism appears to be consistent with the theory of synchronised chaos and is useful for long range predictions of the East African short rains.

Rainfall Mechanisms for the Dominant Rainfall Mode over Zimbabwe Relative to ENSO and/or IODZM

Zimbabwes homogeneous precipitation regions are investigated by means of principal component analysis (PCA) with regard to the underlying processes related to ENSO and/or Indian Ocean Dipole zonal mode (IODZM). Station standardized precipitation index rather than direct rainfall values represent the data matrix used in the PCA. The results indicate that the countrys rainfall is highly homogeneous and is dominantly described by the first principal mode (PC1). This leading PC can be used to represent the major rainfall patterns affecting the country, both spatially and temporarily. The current practice of subdividing the country into the two seasonal rainfall forecast zones becomes irrelevant. Partial correlation analysis shows that PC1 is linked more to the IODZM than to the traditional ENSO which predominantly demonstrates insignificant association with PC1. The pure IODZM composite is linked to the most intense rainfall suppression mechanisms, while the pure El Niño composite is linked to rainfall enhancing mechanisms.

Improved predictability of droughts over southern Africa using the standardized precipitation evapotranspiration index and ENSO

The provision of timely and reliable climate information on which to base management decisions remains a critical component in drought planning for southern Africa. In this observational study, we have not only proposed a forecasting scheme which caters for timeliness and reliability but improved relevance of the climate information by using a novel drought index called the standardised precipitation evapotranspiration index (SPEI), instead of the traditional precipitation only based index, the standardised precipitation index (SPI). The SPEI which includes temperature and other climatic factors in its construction has a more robust connection to ENSO than the SPI. Consequently, the developed ENSO-SPEI prediction scheme can provide quantitative information about the spatial extent and severity of predicted drought conditions in a way that reflects more closely the level of risk in the global warming context of the sub region. However, it is established that the ENSO significant regional impact is restricted only to the period December–March, implying a revisit to the traditional ENSO-based forecast scheme which essentially divides the rainfall season into the two periods, October to December and January to March. Although the prediction of ENSO events has increased with the refinement of numerical models, this work has demonstrated that the prediction of drought impacts related to ENSO is also a reality based only on observations. A large temporal lag is observed between the development of ENSO phenomena (typically in May of the previous year) and the identification of regional SPEI defined drought conditions. It has been shown that using the Southern Africa Regional Climate Outlook Forum’s (SARCOF) traditional 3-month averaged Nino 3.4 SST index (June to August) as a predictor does not have an added advantage over using only the May SST index values. In this regard, the extended lead time and improved skill demonstrated in this study could immensely benefit regional decision makers.

Adaptation to drought in arid and semi-arid environments: Case of the Zambezi Valley, Zimbabwe

Small-scale rain-fed agriculture is the main livelihood in arid to semi-arid regions of sub-Saharan Africa. The area is characterised by erratic rainfall and frequent droughts, making the capacity for coping with temporal water shortages essential for smallholder farmers. Focusing on the Zambezi Valley, Zimbabwe, this study investigates the impact of drought on food security and the strategies used by smallholder farmers to cope with drought. We used meteorological data and interviews to examine the rainfall variability in the study area and the drought-coping mechanisms employed by smallholder famers respectively. The results show that there are various strategies used by smallholder farmers to cope with the impact of drought. These strategies include drought-tolerant crop production, crop variety diversification, purchasing cereals through asset sales, non-governmental organisations’ food aid and gathering wild fruit. However, consecutive droughts have resulted in high food insecurity and depletion of household assets during droughts. Smallholder farmers in the valley have also resorted to a number of measures taken before, during and after the drought. Still, these strategies are not robust enough to cope with this uncertainty.

Taking Children’s Voices in Disaster Risk Reduction a Step Forward

Disaster risk reduction (DRR) continues to gain momentum globally and locally, but there is a notable void in the DRR literature on the role of children in community-level disaster risk management in Zimbabwe. Children are among the most vulnerable groups when disasters occur, yet their voices in disaster risk reduction are rarely heard. Using a qualitative methodology, this article examines the extent to which children are involved in disaster risk reduction in Muzarabani District, Zimbabwe. Despite evidence of the potential positive impact that children can have on DRR, their involvement in risk reduction planning in Zimbabwe is negligible. To achieve greater resilience to disasters requires that children’s voices are heard and recognized as central to improved disaster risk reduction.

A participatory approach in GIS data collection for flood risk management, Muzarabani district, Zimbabwe

Recent attempts to integrate geographic information systems (GIS) and participatory techniques have given rise to terminologies such as participatory GIS and community-integrated GIS. Little has been published about the usefulness of participatory GIS, especially for purposes of flood risk assessment in Zimbabwe. This paper attempts to address this research gap and demonstrates that when combined with participatory methodologies, GIS can provide a mechanism for assessing flood extend in flood-prone communities of Chadereka in Muzarabani communal lands. Flood risk is increasing in the flood-prone areas in Zimbabwe, especially in remote areas where gauging stations are non-existent because of lack of hydrometeorological and climate data for these areas, historical and projected flood events cannot be assessed through modelling. The spatial extent of the flood zone of the December 2007 flash flood event that took place in Chadereka area was mapped using participatory geographic information systems (PGIS), as well as the data collected through interviews that were held with key informants and focus group discussions. Using this approach, a flood extend assessment map was drawn by triangulating the resultant 12 PGIS maps produced by the local community. The results of the study suggest that if conventional GIS and flood modelling is cross checked with PGIS and fieldwork results, the spatial characteristics of floods in ungauged flood-prone areas can be improved and enable the profiling of floods in Chadereka ward.

Southern Africa winter temperature shifts and their link to the Southern Annular Mode

Abstract The main characteristics of spatial and temporal variability of the winter (June–August) observed surface air minimum temperature (SAMT) of southern Africa (Africa south of the equator) were examined from 1960 to 2011. The empirical orthogonal function (EOF) analysis was used to extract the dominant mode of SAMT variability. Statistically significant shifts were detected in both the index derived from the spatially averaged regional SAMT and its EOF1 time coefficients. These discontinuities displayed a sharp rise followed by an abrupt drop during the periods around 1988 and 2007 respectively. The years corresponded to change points in the Southern Annular Mode index where the 1988 significant alteration to a relatively more positive index polarity was followed by a sudden weakening during the latter shift. The development of the warm phase coincided with the decoupling of SAM from SAMT. This occurred when the strengthening of the western ridge of the Mascarene High appeared to be coupled to the creation of anomalously low pressure systems over Angola and the region pole-ward of South Africa. In this epoch, the meridional wind over southern Africa reversed to become predominantly northerly and hence was symptomatic of warm temperature advection from the lower latitudes. However the post 2007 era, though still of indeterminate length, is characterized by a partial return to the pre-1988 circulation conditions. This implies that the impacts of SAM’s epochal alterations have implications not only for the current climate, but also for the interpretation of climate change over southern Africa.

Socio-economic impacts of climate change on subsistence communities

Purpose – This study was conducted to assess the socio-economic implications of climate change on the three ecological regions of Lesotho. In the view that climate change is affecting agriculture, subsistence communities are at risk. The paper aims to discuss these issues. Design/methodology/approach – Two villages were randomly selected from three regions of Lesotho and at least 40 households in each region. The full range of economic activities undertaken was covered to understand how climate affects the communities, and how they are. A livelihood sensitivity matrix was used to determine which resources and livelihoods are most vulnerable to different types of climatic hazards and how the different livelihood activities are impacted by different climate hazards. Findings – A large percentage of the community (>95 percent) was aware of the changing climate and the effects on land productivity. Food crops are the most vulnerable to weather, followed by soil and livestock. Climate variables of major concer...