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The 2014-2018 drought over South Africa's winter rainfall zone (WRZ) created a critical water crisis which highlighted the region's drought and climate change vulnerability. Consequently, it is imperative to better understand the climatic characteristics of the drought in order to inform regional adaptation to projected climate change. In this paper we investigate the spatio-temporal patterns of drought intensity and the recent rainfall trends, focusing on assessing the consistency of the prevailing conceptual model of drought drivers with observed patterns. For this we use the new spatial subdivision for the region encompassing the WRZ introduced in our companion paper (Conradie et al., 2022). Compared to previous droughts since 1979, the 2014-2018 drought in the WRZ core was characterised by a markedly lower frequency of very wet days (exceeding the climatological 99.5th percentile daily rainfall -- including dry days) and of wet months (SPI1 > 0:5), a sub-seasonal attribute not previously reported. There was considerable variability in the spatial footprint of the drought. Short-term drought began in the south-western core WRZ in spring 2014. The peak intensity gradually spread north-eastward, although a spatially near-uniform peak is seen during mid-2017. The overall drought intensity for the 2015--2017 period transitions radially from most severe in the WRZ core to least severe in the surroundings. During 2014 and 2015, the drought was most severe at those stations receiving the largest proportion of their rainfall from westerly and north-westerly winds; by 2018, those stations receiving the most rain from the south and south-east were most severely impacted. This indicates an evolving set of dynamic drivers associated with distinct rain-bearing synoptic flows. No evidence is found to support the suggestion that the drought was more severe in the mountain catchments of Cape Town's major supply reservoirs than elsewhere in the core nor that rain day frequency trends since 1979 are more negative in this subdomain. Rainfall and rain day trend rates also exhibit some connections to the spatial seasonality structure of the WRZ, although this is weaker than for drought intensity. Caution should be applied in assessing South African rain day trends given their high sensitivity to observed data shortcomings. Our findings suggest an important role for zonally asymmetric dynamics in the region's drought evolution. This analysis demonstrates the utility of the spatial subdivisions proposed in the companion paper by highlighting spatial structure in drought intensity evolution linked to rainfall dynamics. [ABSTRACT FROM AUTHOR]

A renewed focus on southern Africa's winter rainfall zone (WRZ) following the Day Zero drought and water crisis has not shed much light on the spatial patterns of its rainfall variability and climatological seasonality. However, such understanding remains essential in studying past and potential future climate changes. Using a dense station network covering the region encompassing the WRZ, we study spatial heterogeneity in rainfall seasonality and temporal variability. These spatial patterns are compared to those of rainfall occurring under each ERA5 synoptic-scale wind direction sector. A well-defined "true" WRZ is identified with strong spatial coherence between temporal variability and seasonality not previously reported. The true WRZ is composed of a core and periphery beyond which lies a transition zone to the surrounding year-round rainfall zone (YRZ) and late summer rainfall zone. In places, this transition is highly complex, including where the YRZ extends much further westward along the southern mountains than has previously been reported. The core receives around 80% of its rainfall with westerly or north-westerly flow compared to only 30% in the south-western YRZ incursion, where below-average rainfall occurs on days with (usually pre-frontal) north-westerly winds. This spatial pattern corresponds closely to those of rainfall seasonality and temporal variability. Rainfall time series of the core and surroundings are very weakly correlated (R² < 0:1), also in the winter half-year, implying that the YRZ is not simply the superposition of summer and winter rainfall zones. In addition to rain-bearing winds, latitude and annual rain day climatology appear to influence the spatial structure of rainfall variability but have little effect on seasonality. Mean annual rainfall in the true WRZ exhibits little association with the identified patterns of seasonality and rainfall variability despite the driest core WRZ stations being an order of magnitude drier than the wettest stations. This is consistent with the general pattern of near homogeneity within the true WRZ, in contrast to steep and complex spatial change outside it. [ABSTRACT FROM AUTHOR]

The multi‐year (2015–2017) drought in the South West of the Western Cape (SWC) caused a severe water shortage in the summer of 2017–2018, with damaging impacts on the local and regional economy, and Cape Town being in the news one of the first major cities to potentially run out of water. Here, we assess the links between the rainfall deficits during the drought and (a) large scale circulation patterns, (b) moisture transport, and (c) convective available potential energy (CAPE). We used self‐organising maps (SOM) analysis to classify daily ERA‐interim 850 hPa geopotential height for the period 1979–2017 (March–October) into synoptic types. This allowed us to identify the dominant synoptic states over Southern Africa that influence the local climate in the area affected by the drought. The results show that (a) the frequency of nodes with rain‐bearing circulation types decreased during the drought; (b) the amount of rain falling on days that did have rain‐bearing circulation types was reduced, especially in the shoulder seasons (March–May and August–October); (c) the rainfall reduction was also associated with anomalously low moisture transport, and convective energy (CAPE), over SWC. These results add to the existing knowledge of drivers of the Cape Town drought, providing an understanding of underlying synoptic processes. [ABSTRACT FROM AUTHOR]

We analyse long‐term (1900–2017) rainfall data in the southern part of the winter rainfall region of southern Africa to understand the spatial patterns of recent and long‐term trends and contextualize the 2015–2017 rainfall anomalies which led to the so‐called "Day Zero" drought in Cape Town. Our analyses reveal cohesive spatial patterns and seasonal differences in rainfall trends across a range of timescales. These suggest that rainfall is subject to regional driving mechanisms, predominantly manifested at the 20–50 year timescale, but the influence of these mechanisms is modified by subregional and seasonally specific processes, frequently resulting in trends of different magnitudes and even sign. Trend patterns are consistent with multidecadal‐scale quasi‐periodicity, with only the most recent phase (post‐1981 drying) corresponding to the expected regional response to hemispheric processes linked to anthropogenic climate change. The spatial and seasonal patterns of drying observed since 1981 alone do not explain the pattern of 2015–2017 drought anomalies, although they share a strong autumn and weak mid‐winter signal. These results have implications to the interpretation of drought in the context of observed rainfall trends. Furthermore, we identify directions for improvement of the conceptual understanding of drivers of rainfall variability and the role of anthropogenic climate change in the winter rainfall region of South Africa. [ABSTRACT FROM AUTHOR]

Spatial ecological models of wetland systems are important tools for evaluating system response to changes in hydrological inputs, arising from anthropogenic manipulation or climate change. We present an approach using multiple species distribution models (SDMs) for floodplain macrophytes, based on empirical relationships with flood duration. 27 indicator species were identified for four floodplain classes in a seasonally pulsed distributary of the Okavango Delta, based on data from a field survey of 30 floodplain sites. Spatial hydrological history was constructed using a combination of Landsat and MODIS imagery, and ground-truthing. Relationships between duration and occurrence were used to construct general linear probability models (GLMs) of species along the hydroperiod gradient. The GLM parameters were then used to construct SDMs driven by a spatial hydrological model, which generates annual assessments of inundation duration in months in each 1km2 cell across the Delta. The modelled distribution fits were mostly robust (18 GLMs had p < 0.05). Tests of model performance against a validation set of five floodplain sites showed an average of 87% correct predictions of presence. The strong performance of the models and the ability to produce map-based and quantitative output indicate good potential for use in assessment of basin development scenarios. [ABSTRACT FROM AUTHOR]

A simple reaction time (SRT) difference between responses to visual stimuli presented ipsilaterally and contralaterally to the responding hand, known as the Poffenberger effect or the crossed–uncrossed difference (CUD), has been commonly interpreted as a measure of interhemispheric transfer time (IHTT). However, the validity of this interpretation and the measure's reliability have been debated. The present study aimed at obtaining reliable evidence of the influence of spatial attention on the CUD, which would provide an argument against the classical interpretation of CUD. To meet the high statistical power requirements, over 100 thousand SRTs in total were collected from 12 participants. The task had three stimulus presentation conditions differing in the degree of stimulus location uncertainty: blocked (no uncertainty), randomized (full uncertainty), and mixed (25% uncertainty). The results showed robust effects of location uncertainty, proving spatial attention's contribution to the CUD. Further, we observed a strong visual-field asymmetry reflecting the right hemisphere specialization in target detection and spatial reorienting. Lastly, despite exceptional reliability of the component SRT measures, the CUD reliability was still too low to justify using this measure as an index of individual differences. • Very large CUD study, over 100 thousand RTs in total, collected from 12 participants. • Spatial attention modulates CUD. • The notion of CUD as rigid interhemispheric transmission time is an oversimplification. • Behavioral CUD is not reliable enough to measure individual differences. [ABSTRACT FROM AUTHOR]

Self-Organizing Maps (SOM) based classifications of synoptic circulation patterns are increasingly being used to interpret large-scale drivers of local climate variability, and as part of statistical downscaling methodologies. These applications rely on a basic premise of synoptic climatology, i.e. that local weather is conditioned by the large-scale circulation. While it is clear that this relationship holds in principle, the implications of its implementation through SOM-based classification, particularly at interannual and longer time scales, are not well recognized. Here we use a SOM to understand the interannual synoptic drivers of climate variability at two locations in the winter and summer rainfall regimes of South Africa. We quantify the portion of variance in seasonal rainfall totals that is explained by year to year differences in the synoptic circulation, as schematized by a SOM. We furthermore test how different spatial domain sizes and synoptic variables affect the ability of the SOM to capture the dominant synoptic drivers of interannual rainfall variability. Additionally, we identify systematic synoptic forcing that is not captured by the SOM classification. The results indicate that the frequency of synoptic states, as schematized by a relatively disaggregated SOM (7 × 9) of prognostic atmospheric variables, including specific humidity, air temperature and geostrophic winds, captures only 20-45% of interannual local rainfall variability, and that the residual variance contains a strong systematic component. Utilising a multivariate linear regression framework demonstrates that this residual variance can largely be explained using synoptic variables over a particular location; even though they are used in the development of the SOM their influence, however, diminishes with the size of the SOM spatial domain. The influence of the SOM domain size, the choice of SOM atmospheric variables and grid-point explanatory variables on the levels of explained variance, is consistent with the general understanding of the dominant processes and atmospheric variables that affect rainfall variability at a particular location. [ABSTRACT FROM AUTHOR]

Characterising inundation conditions for flood-pulsed wetlands is a critical first step towards assessment of flood risk as well as towards understanding hydrological dynamics that underlay their ecology and functioning. In this paper, we develop a series of inundation maps for the Okavango Delta, Botswana, based on the thresholding of the SWIR band (b7) MODIS MCD43A4 product. We show that in the Okavango Delta, SWIR is superior to other spectral bands or derived indices, and illustrate an innovative way of defining the spectral threshold used to separate inundated from dry land. The threshold is determined dynamically for each scene based on reflectances of training areas capturing end-members of the inundation spectrum. The method provides a very good accuracy and is suitable for automated processing. [ABSTRACT FROM AUTHOR]

In the present essay, the first in a short cycle, the author reviews and comments on the problems students and researchers have with proper understanding of the basics of statistical inference. Those difficulties seem to be in part due to mixing of the opposing theoretical stances of Fisher and Neyman, reviewed shortly. The author believes that the inconsistent standards of statistical inference afflict the teaching of methodology particularly. [ABSTRACT FROM AUTHOR]

One of the more prominent problems of significance testing is ritualisation of their practical use and interpretation. In the present, third part of the series, reasons and manifestations of that rigidity have been discussed, and an alternative, sometimes labeled "statistical thinking", presented. Matching a statistical significance testing scenario to the needs of the specific research program constitutes a part of statistical thinking. Some typical scenarios have been described, with the intent of showing how the same statistical tool, depending on it's assumptions, can have differing use in research. [ABSTRACT FROM AUTHOR]

The second of the series of essays on the problems of significance testing in psychological research focuses on inconsistencies of the logic of these tests and resulting problems with interpretation. The limits of their practical usability have been discussed, and reasons of their failure with a priori unlikely null-hypotheses explained. Misleading connotations of the term "statistical significance" have been stressed, that obscure the true meaning of statistical significance and promote bad practices, including overestimation of significance, and neglecting the problem of effect size. [ABSTRACT FROM AUTHOR]

Summary The Okavango Delta of Botswana is a large arid-zone wetland comprising 20,000 km 2 of permanent and seasonal floodplains and over 100,000 islands. It has been shown that island groundwater can have very high dissolved arsenic (As) concentration, but the abiotic and biotic controls on As mobility are not well understood in this setting. At New Island, an island located in the seasonal swamp, dissolved As concentration increased from below detection limits in the surface water to 180 μg/L in groundwater, present as As(III) species. We investigated the relative importance of hydrologic, geochemical, and geomicrobial processes, as well as influences of recent extreme flooding events, in mobilizing and sequestering As in the shallow groundwater system under this island. Our results suggest that evapotranspiration and through-flow conditions control the location of the high arsenic zone. A combination of processes is hypothesized to control elevated As in the concentration zone of New Island: high evapotranspiration rates concentrate As and other solutes, more alkaline pH leads to desorption of arsenic or dissolution of arsenic sulfides, and formation of thioarsenic complexes acts to keep arsenic in solution. Evidence from X-ray absorption near-edge structure spectroscopy (XANES) and sulfate reducing bacteria (SRB) measurements further suggests that SRBs influence arsenic sequestration as orpiment (As 2 S 3 ). Although dissolved organic matter (DOM) was not significantly correlated to dissolved As in the groundwater, our results suggest that DOM may serve as an electron donor for sulfate reduction or other microbial reactions that influence redox state and As mobility. These results have important implications for water management in the region and in other large wetland environments. The processes evaluated in this study are also relevant for arsenic removal in subsurface constructed wetland systems that may exhibit rapidly changing processes over small spatial scales. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assess role of anthropogenic climate change in recent floods in the Okavango basin. [•] Hydrological model is forced with simulated current and pre-industrial climates. [•] Anthropogenic climate change has reduced probability of high floods in the Okavango. [•] Reduction is due to increased evaporation; rainfall changes are minor. [Copyright &y& Elsevier]

Abstract: The annual flood cycle in the Okavango Delta is the basis of subsistence of the local population, providing water, arable land and wetland resources. Additionally, it forms the basis of a large tourism industry. Flooding in the Okavango Delta is, however, very variable both at short and long term time scales. Past research suggested the influence of factors such as tectonic activity, sedimentation, vegetation change or human influence on the spatial distribution of floodwaters. Change in the flooding regime at any given site is thus often perceived as an effect of permanent change in the system, and this perception results in unnecessary demands for engineering interventions in the system. However, it is possible that some of the perceived changes in flood regime are apparent transient effects of non-linearity of the system and variation in hydrological inputs. Hydrometric data and satellite-derived flood maps are analysed here using statistical methods (covariance analysis and double mass analysis) to distinguish between temporal and permanent changes in various parts of the Okavango Delta. The analyses reveal that system non-linearity causes the hydrological responses of the Okavango Delta to be non-proportional to the inputs. Periods of one to several consecutive years are present when flood extents and outflows are either considerably higher or lower (flow or flood regimes) than what would be expected considering the magnitude of inflow. Such effects are visible throughout the entire system, or only in some distributaries, and do not, as previously thought, represent permanent change in flood distribution. However, flood regime change that appears to result from a physical change in the system has been detected. This change has a nature of shift in flood distribution between the Thaoge and the Xudum, with the latter receiving more water after 1997 at the expense of the former and causing 2004 re-flooding of Lake Ngami. [Copyright &y& Elsevier]

Anthropogenic climate change likely influences the beginning of 2020 growing season's water deficit in parts of southern Africa, with severe consequences to food security. GLO:EVN/01may20:gcb15047-toc-0001.jpg PHOTO (COLOR): . gl The failure of early (October-December) rains, amidst a multiyear drought, has raised concerns of a potential emerging food security crisis in parts of southern Africa, with an estimated 45 million people at risk of severe food insecurity (WFP (World Food Programme), [12]). 2 a Indices calculated from region-average rainfall and mean temperature-derived Thorthwaite PET, with 1948-1980 normalization period, by fitting Gamma distribution for rainfall, and log-logistic distribution for PET. [Extracted from the article]

Summary: Changes in hydrological inputs to the flood-pulsed Okavango Delta result in changes in such flooding characteristics as floodplain water depth, inundation duration and frequency. A mathematical model is used to assess impacts of changing hydrological inputs on flooding in the Okavango Delta. Future conditions are simulated by superimposing simulated abstractions, upstream developments and climate change effects on the observed time series of hydrological inputs. The effects of change in inputs are then determined by comparing hydrological characteristics such as inundation duration and frequency derived from the original and modified time series of model outputs. Simulations show that upstream abstractions are likely to have small short-term effects on the flooding pattern in the Delta, while other upstream developments such as damming or deforestation have more pronounced effects. All of these effects are relatively small, however, when compared to changes resulting from existing climatic variability, and those from the possible effects of future climate change. The combined effects of human abstraction and climate change, manifested as increased temperatures, decreased rainfall, and reduction in river flows, may result in significant Delta drying. The simulated hydrological changes affect the Delta floodplain ecosystems, with anticipated changes in the area and proportions of permanent swamp, areas covered by sedge and grass vegetation (seasonal floodplains) and floodplain grasslands (intermittently flooded areas). These will have varied effects on ecological processes in the Delta, in particular vegetative succession, primary production, and relationships of floodplains with the surrounding woodland and savannah. Additional ripple effects up trophic levels can also be expected. There may also be downstream impacts on tourist facilities presently on the fringes of the seasonal swamps as a result of reduced or increased flooding. As a result of altered flood regime, some effects are also anticipated with respect to the recharge of aquifers, which are currently used for drinking water supply around the Delta. [Copyright &y& Elsevier]

Abstract: Annual inflows and outflows from the Okavango Delta are analysed for possible changes over time. The magnitude of inflows determines the area inundated annually over the delta, and therefore the delta ecosystem on which the thriving tourism depends. Inhabitants of the delta area greatly depend on harvesting aquatic and terrestrial resources, and the abundance of these resources is affected by flooding. Annual flows, annual maximum flows, and annual minimum flows of the Okavango River are analysed for the presence of abrupt or gradual changes and cycles in order to establish the nature of these perceived changes. Change points have been identified in annual flows of the Okavango River and Zambezi River. Other time series except the annual minimum flows are free of trends. Significant cycles were identified on annual flows, annual maximum flows, and annual minimum flows of both the Okavango and Zambezi Rivers. Residuals obtained after removing the cyclic component from each of these time series are trend free. The apparent decline of inflows into the Okavango Delta is explained by the existence of this cyclic component, rather than gradual or abrupt decline in flows over time. The cyclic component identified on the Okavango River has a regional scale as flows on the neighbouring Zambezi River have similar features. Possible causes of the cyclic behaviour are not known. [Copyright &y& Elsevier]

Climate-induced food production shocks, like droughts, can cause food shortages and price spikes, leading to food insecurity. In 2007, a synchronous crop failure in Lesotho and South Africa—Lesotho's sole trading partner—led to a period of severe food insecurity in Lesotho. Here, we use extreme event attribution to assess the role of climate change in exacerbating this drought, going on to evaluate sensitivity of synchronous crop failures to climate change and its implications for food security in Lesotho. Climate change was found to be a critical driver that led to the 2007 crisis in Lesotho, aggravating an ongoing decline in food production in the country. We show how a fragile agricultural system in combination with a large trade-dependency on a climatically connected trading partner can lead to a nonlinear response to climate change, which is essential information for building a climate-resilient food-supply system now and in the future. [ABSTRACT FROM AUTHOR]

1. Flood-pulsed wetlands make vital contributions to local and global biodiversity. However, the patterns and controls of spatial and temporal variation in aquatic biodiversity in flood-pulsed wetlands are not well understood. We analysed the relationship between variation in hydrological regime and the patterns of aquatic biodiversity in a large pristine flood-pulsed wetland, the Okavango Delta, Botswana. 2. Surveys of water chemistry, diatoms and macroinvertebrates were conducted over the seasonal phases of the flood pulse. Hydrological variables of flood frequency and hydroperiod class were collated from 16 years of satellite images. Multivariate regression trees and generalised least squares regression were used to determine the chief controls of community composition and taxon richness. 3. Hydroperiod class, phase of the flood and conductivity explained 32% and 43% of the variation in diatom and invertebrate taxon richness, respectively. There was a negative relationship between hydroperiod class and invertebrate taxon richness on the rising, peak and receding flood, whereas at low flood there was no significant relationship. Multivariate regression tree analysis revealed hydroperiod class, phase of the flood and conductivity as the dominant forces shaping invertebrate and diatom community composition. 4. Seasonal and spatial variation in hydrological conditions are the principal drivers of variation in aquatic biodiversity in flood-pulsed wetlands. In pristine flood-pulsed wetlands, increased productivity caused by the arrival of the flood waters appears to override disturbance and connectivity in shaping taxon richness and community composition. Thus, these data suggest that the maintenance of a rich mosaic of habitats covering a broad range of hydroperiod is the key to preserving aquatic biodiversity and natural ecosystem function in flood-pulsed wetlands. [ABSTRACT FROM AUTHOR]

Vegetative response aspects of climate change studies include the determination of vegetation cover changes across climatic gradients. Vegetation characteristics and soil moisture measurements were obtained from four locations with decreasing rainfall along the Botswana Kalahari transect. These are referred to as Pandamatenga, (698 mm year−1), Maun (460 mm year−1), Okwa (407 mm year−1) and Tshane (365 mm year−1). Trends in major vegetative cover and soil components included species types and richness assessments which reflected certain changes southward but also showed interesting degrees of variability. This occurred despite the apparent homogeneity of the Kalahari sands and predominantly semi-arid savanna shrub–woodland vegetation cover. Despite linear decreases, both in rainfall and soil moisture content, results indicated high soil moisture variability at the Okwa location which relates to unique climatic and geological factors. Also many species are unique to specific locations for instance Pandametanga is characterized by Zambesian species while the Maun location is characterized by Colophosphermum mopane. This changes southwards as Acacias become more dominant and significantly co-occur with Grewia flava. While the average total numbers of plants decreased, total numbers of different species varied little from the wetter to the drier end of the moisture gradient. The association between rainfall and woody cover is negative implying that canopy cover extents (in terms of vegetation density) increase along the gradient due to increases in bush encroachment in drier areas. Therefore, while representing a continuum in terms of species numbers, in other respects (e.g. species types and ground cover components) vegetation zones in the Kalahari may be regarded as discontinuous units. Differences between mapped vegetation zones may be accounted for in terms of relatively unique ecosystem factors which function partly in response to geological conditions and partly in response to local (as opposed to regional) climatic factors. This appears to have led to ecosystem adaptive measures (in terms of species responses) rarely mirrored elsewhere along the gradient. Hence adaptability in terms of species migrations in response to relatively rapid climate changes may not readily take place over the Kalahari in Botswana. [Copyright &y& Elsevier]

The science of event attribution has emerged to routinely answer the question whether and to what extent human-induced climate change altered the likelihood and intensity of recently observed extreme weather events. In Europe a pilot program to operationalize the method started in November 2019, highlighting the demand for timely information on the role of climate change when it is needed most: in the direct aftermath of an extreme event. Independent of whether studies are provided operationally or as academic studies, the necessity of good observational data and well-verified climate models imply most attributions are currently made for highly developed countries only. Current attribution assessments therefore provide very little information about those events and regions where the largest damages and socio-economic losses are incurred. Arguably, these larger damages signify a much greater need for information on how the likelihood and intensity of such high-impact events have been changing and are likely to change in a warmer world. In short, why do we not focus event attribution research efforts on the whole world, and particularly events in the developing world? The reasons are not just societal and political but also scientific. We simply cannot attribute these events in the same probabilistic framework employed in most studies today. We outline six focus areas to lessen these barriers, but we will not overcome them in the near future. [ABSTRACT FROM AUTHOR]

As established in earlier research, analysis of the combined roles (co-behavior) of multiple climate processes provides useful insights into the drivers of regional climate variability, especially for regions with no singular large-scale circulation control. Here, we extend the previous study in order to examine the performance of eight models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) in representing co-behavior influence on surface expressions over southern Africa. We find that although models broadly simulate observed precipitation responses over southern Africa, they fail to produce statistically strong response signals for an important drought pattern (El Niño co-behaving with positive Antarctic Oscillation during summer) for the region. We also demonstrate that the models show statistically strong temperature response signals to co-behavior that agree well with observed responses over the region. The multimodel ensemble mean although consistent with observations shows a larger spread. By elucidating the performance of models in representing observed co-behavior of climate processes, we are able to evaluate models while establishing important information for understanding of climate variability. [ABSTRACT FROM AUTHOR]

In the context of ongoing climate change, extreme weather events are drawing increasing attention from the public and news media. A question often asked is how the likelihood of extremes might have changed by anthropogenic greenhouse-gas emissions. Answers to the question are strongly influenced by the model used, duration, spatial extent, and geographic location of the event—some of these factors often overlooked. Using output from four global climate models, we provide attribution statements characterised by a change in probability of occurrence due to anthropogenic greenhouse-gas emissions, for rainfall and temperature extremes occurring at seven discretised spatial scales and three temporal scales. An understanding of the sensitivity of attribution statements to a range of spatial and temporal scales of extremes allows for the scaling of attribution statements, rendering them relevant to other extremes having similar but non-identical characteristics. This is a procedure simple enough to approximate timely estimates of the anthropogenic contribution to the event probability. Furthermore, since real extremes do not have well-defined physical borders, scaling can help quantify uncertainty around attribution results due to uncertainty around the event definition. Results suggest that the sensitivity of attribution statements to spatial scale is similar across models and that the sensitivity of attribution statements to the model used is often greater than the sensitivity to a doubling or halving of the spatial scale of the event. The use of a range of spatial scales allows us to identify a nonlinear relationship between the spatial scale of the event studied and the attribution statement. [ABSTRACT FROM AUTHOR]

The effect of slower responses to validly than invalidly cued targets is known as inhibition of return (IOR). Opposing accounts of IOR have been proposed: one postulates a singular phenomenon explained by oculomotor mechanisms alone, while the other, more diverse account postulates both perceptual-cognitive and motor factors. In our research we considered the relation between motor programming and IOR. In an extended replication of an earlier study, using an eye abduction technique we restricted eye movement in the temporal half-space; this resulted in IOR attenuation in that area, compared to the unrestricted, nasal part of the visual field. Our results contradict the earlier result and demonstrate that IOR does depend on preparation of eye movement, as predicted by the oculomotor priming hypothesis. [ABSTRACT FROM AUTHOR]

The role of in-stream aquatic vegetation as ecosystem engineers in the distribution of organic matter was investigated in the Okavango Delta, one of the world's largest oligotrophic wetlands. The Okavango channel beds are covered up to 50% with submerged macrophyte patches. By accumulating and concentrating organic matter in the sediments below the patches, macrophytes are likely able to locally forestall a deficiency of nutrients. Up to 21 times more N, 18 times more C, 13 times more P and 6 times more Si can be found in vegetated sediments compared to non-vegetated sediments. Nutrient specific accumulation relates to its relative scarcity in the overlaying water. There is a depletion of dissolved N relative to P, whereas Si is relatively abundant. The Okavango Delta water can generally be characterised as oligotrophic based on plant species composition (e.g. presence of carnivorous plants and absence of floating plants), low plant N:P ratios, and low nutrient- and element-concentrations. Local mineralization and intensified nutrient cycling in the sediments is hypothesized to be crucial for the macrophytes' survival because it provides a key source of the essential nutrients which plants otherwise cannot obtain in sufficient quantities from the nutrient poor water. By engineering the ecosystem as such, channel vegetation also retards the loss of elements and nutrients to island groundwater flow, contributing to one of the key processes driving the high productivity of the Okavango Delta, making it unique among its kind. [ABSTRACT FROM AUTHOR]

Water chemistry is important for the maintenance of wetland structure and function. Interpreting ecological patterns in a wetland system therefore requires an in-depth understanding of the water chemistry of that system. We investigated the spatial distribution of chemical solutes both in soil pore water and surface water, along island-floodplain-channel hydrological gradients in seasonally and permanently inundated habitats between major regions in the Okavango Delta, Botswana. Our results show that major cations (Ca, Na, Mg, and K), dissolved silica (DSi), dissolved boron (B), dissolved organic matter (DOC) and electrical conductivity increased significantly, at p ≤ 0.05, from the inlet of the Delta (the Panhandle) to the distal downstream reaches, suggesting the influence of evapoconcentration. Concentrations of dissolved Fe, Al, Zn, Cu, and Mn significantly decreased, at p ≤ 0.05, from the inflow of the Delta to the distal reaches. Only Na, Mn, Fe, Al, and DOC showed significant differences, at p ≤ 0.05, along the local floodplain-channel hydrological gradients, with higher solute concentrations in the floodplains than the channels. Solute concentrations in soil water exhibited similar distribution patterns to those in surface water, but concentrations were higher in soil water. Based on the results, we hypothesise that floodplain emergent vegetation and the channel-fringing vegetation in the Panhandle (a faultbounded entry trough to the Delta) and the permanently inundated eco-region together influence the cycling of solutes that enter the Delta through uptake. [ABSTRACT FROM AUTHOR]

Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (δ 30 Si) may be a useful tool to investigate these processes. Here, we present 82 δ 30 Si measurements from surface waters, pore waters, biogenic silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland. Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. δ 30 Si in dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19‰), implying the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi δ 30 Si ( n = 30) ranges from −1.49‰ to +0.31‰ and during dissolution, residual BSi tends towards higher δ 30 Si. The data permit a field-based estimate of the fractionation associated with BSi dissolution, ε 30 BSi-DSi = −0.26‰, though it is unclear if this is an artefact of the process of dissolution. Clay δ 30 Si ranges from −0.97‰ to +0.10‰, ( n = 15, mean = −0.31‰) and include the highest values yet published, which we speculate may be due to an equilibrium isotope effect during diagenetic transformation of BSi. Two key trends in surface water DSi δ 30 Si merit further examination: declining δ 30 Si in an area roughly corresponding to the permanent floodplains despite net DSi removal, and increasing δ 30 Si in the area corresponding to the seasonal floodplains. We infer that evaporative enrichment of surface waters creates two contrasting regimes. Chemical weathering of low δ 30 Si phases releases low δ 30 Si DSi in the relatively dilute waters of the permanent floodplains, whereas silicon removal via clay formation or vegetation uptake is the dominant process in the more enriched, seasonal floodplains. [ABSTRACT FROM AUTHOR]

Highlights: [•] Water security problems are affecting households in different settlements of Botswana. [•] High evaporation rates and poor rainfall are negatively affecting water security. [•] Power cuts and lack of specialized equipment for water negatively affect water supply. [•] Water governance institutions in Ngamiland are not effective in the management of water. [•] Water supply providers lack financial resources to invest in the appropriate infrastructure. [Copyright &y& Elsevier]

Abstract: Despite the fact that hemispheric asymmetry of attention has been widely studied, a clear picture of this complex phenomenon is still lacking. The aim of the present study was to provide an efficient and reliable measurement of potential hemispheric asymmetries of three attentional networks, i.e. alerting, orienting and executive attention. Participants (N =125) were tested with the Lateralized Attention Network Test (LANT) that allowed us to investigate the efficiency of the networks in both visual fields (VF). We found a LVF advantage when a target occurred in an unattended location, which seems to reflect right hemisphere superiority in control of the reorienting of attention. Furthermore, a LVF advantage in conflict resolution was observed, which may indicate hemispheric asymmetry of the executive network. No VF effect for alerting was found. The results, consistent with the common notion of general right hemisphere dominance for attention, provide a more detailed account of hemispheric asymmetries of the attentional networks than previous studies using the LANT task. [Copyright &y& Elsevier]

Summary: This paper studies the interactions of density driven flow and geochemical reactions under evapo-concentration. A numerical model that couples the relevant flow, transport and chemical processes was used to analyze density-driven flow on islands in the Okavango Delta, Botswana. Evapo-concentration on the islands leads to steadily increasing solute concentrations until the onset of density-driven flow against the evaporation-induced upward flow. The modelling results suggest that lag times to the onset of density-driven flow are strongly influenced by geochemical reactions. Mineral precipitation and carbon dioxide de-gassing increase the lag time. Carbon dioxide de-gassing is enhanced if humic substances are present at elevated concentrations. Simulation results were shown to be most sensitive to the longitudinal dispersivity. Modelling results are compared to field observations from three islands in the Okavango Delta. A semi-quantitative correspondence between modelled and observed concentration patterns is established for the major chemical constituents. [Copyright &y& Elsevier]

• Drought had most extensive impacts in parts of South Africa, Namibia and Botswana. • The response of vegetation to drought is weaker in Angola, Malawi and Madagascar. • The Community Earth System Model underestimates the magnitudes of drought impacts. • The model ensemble show a spread in vegetation response across biomes and seasons. Drought is a frequent disturbance in many regions of the globe and can have a particularly severe impact on vegetation. Over southern Africa, where drought is a regular occurrence, relatively little is known about how quickly vegetation responds to droughts. We characterized the meteorological drought occurrence in southern Africa from 1981 to 2005 and examined the impacts on vegetation productivity, as derived from satellite data. The spatio-temporal extent and severity of droughts were assessed at different timescales (1- to 18-month timescales) using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI). Thereafter, we examined the impacts of droughts on southern African vegetation using the Normalized Difference Vegetation Index (NDVI). The results of this study show that southern African vegetation responds differently to drought over the different timescales. During the 1981–2005 period, droughts had extensive impacts over central parts of South Africa, Namibia and western areas of Botswana and the responses of vegetation varied according to season and biome, likely due to the differences in the levels of water needed by vegetation during various growth/phenological phases. In addition, the magnitude of the drought's impact on vegetation is sensitive to the type of drought index that is used to characterize its severity. We further investigated the response of vegetation as simulated by an Earth System Model (the Community Earth Systems Model, CESM) over the same period. The intensity of drought impacts on vegetation is underestimated by CESM, while the timescales at which vegetation responds to droughts are overestimated by it. Different model ensemble members show a substantial spread in the simulation of vegetation response across different biomes and seasons, which may be due to inherent errors and biases in the land component of the model (CLM4.5), or in the atmospheric model and/or the parameterizations. However, we demonstrate that the land component of the CESM (CLM4.5) does provide an adequate representation of the response of vegetation to drought and would provide useful information about the response of vegetation to future drought. If the uncertainties we identified could be reduced, a more realistic simulation of the vegetation response to drought could be realized. [ABSTRACT FROM AUTHOR]