Parameter and input data uncertainty estimation for the assessment of water resources in two sub-basins of the Limpopo River Basin

The demand for water resources is rapidly growing, placing more strain on access to water and its management. In order to appropriately manage water resources, there is a need to accurately quantify available water resources. Unfortunately, the data required for such assessment are frequently far from sufficient in terms of availability and quality, especially in southern Africa. In this study, the uncertainty related to the estimation of water resources of two sub-basins of the Limpopo River Basin – the Mogalakwena in South Africa and the Shashe shared between Botswana and Zimbabwe – is assessed. Input data (and model parameters) are significant sources of uncertainty that should be quantified. In southern Africa water use data are among the most unreliable sources of model input data because available databases generally consist of only licensed information and actual use is generally unknown. The study assesses how these uncertainties impact the estimation of surface water resources of the sub-basins. Data on farm reservoirs and irrigated areas from various sources were collected and used to run the model. Many farm dams and large irrigation areas are located in the upper parts of the Mogalakwena sub-basin. Results indicate that water use uncertainty is small. Nevertheless, the medium to low flows are clearly impacted. The simulated mean monthly flows at the outlet of the Mogalakwena sub-basin were between 22.62 and 24.68 Mm3 per month when incorporating only the uncertainty related to the main physical runoff generating parameters. The range of total predictive uncertainty of the model increased to between 22.15 and 24.99 Mm3 when water use data such as small farm and large reservoirs and irrigation were included. For the Shashe sub-basin incorporating only uncertainty related to the main runoff parameters resulted in mean monthly flows between 11.66 and 14.54 Mm3. The range of predictive uncertainty changed to between 11.66 and 17.72 Mm3 after the uncertainty in water use information was added

Modelling of channel transmission loss processes in semi-arid catchments of southern Africa using the Pitman Model

Water availability is one of the major societal issues facing the world. The ability to understand and quantify the impact of key hydrological processes, on the availability of water resources, is therefore integral to ensuring equitable and sustainable resource management. Channel transmission losses are an under-researched hydrological process that affects resource availability in many semi-arid regions such as the Limpopo River Basin in southern Africa, where the loss processes amount to approximately 30 % of the water balance. To improve the understanding of these loss processes and test the capability of modelling routines, three approaches using the Pitman model are applied to selected alluvial aquifer environments. The three approaches are an explicit transmission loss function, the use of a wetland function to represent channel-floodplain storage exchanges and the use of a dummy reservoir to represent floodplain storage and evapotranspiration losses. Results indicate that all three approaches are able to simulate channel transmission losses with differing impacts on the regional flows. A determination of which method best represents the channel transmission losses process requires further testing in a study area that has reliable observed historical records

Learning from South Africa's recent summer rainfall droughts: How might we think differently about response?

The 2015/2016 and 2016/2017 summer rainfall seasons in South Africa, as well as in the Southern African Development Community region more widely, are generally agreed to be the most severe droughts on record since those of the early 1980s and 1990s. Shortcomings of a more reactive approach to dealing with drought have been well covered in the literature, yet evolution in this regard remains slow. South Africa is currently in the midst of significant change at the local governmental level, as well as likely ongoing change at the national scale. As a result, this provides a potential opportunity to think differently about drought response, taking a longer term and more proactive view, also informed by longer term climate change projections. This commentary provides selected examples of where such an approach might be taken, concluding with hope for an expanded role for scientists in better informing response.Natural Environment Research Council (NE/M02007X/1)http://wileyonlinelibrary.com/journal/area2021-09-01hj2019Geography, Geoinformatics and Meteorolog

Natural Hazards in a Changing World: A Case for Ecosystem-Based Management

<div><p>Communities worldwide are increasingly affected by natural hazards such as floods, droughts, wildfires and storm-waves. However, the causes of these increases remain underexplored, often attributed to climate changes or changes in the patterns of human exposure. This paper aims to quantify the effect of climate change, as well as land cover change, on a suite of natural hazards. Changes to four natural hazards (floods, droughts, wildfires and storm-waves) were investigated through scenario-based models using land cover and climate change drivers as inputs. Findings showed that human-induced land cover changes are likely to increase natural hazards, in some cases quite substantially. Of the drivers explored, the uncontrolled spread of invasive alien trees was estimated to halve the monthly flows experienced during extremely dry periods, and also to double fire intensities. Changes to plantation forestry management shifted the 1∶100 year flood event to a 1∶80 year return period in the most extreme scenario. Severe 1∶100 year storm-waves were estimated to occur on an annual basis with only modest human-induced coastal hardening, predominantly from removal of coastal foredunes and infrastructure development. This study suggests that through appropriate land use management (e.g. clearing invasive alien trees, re-vegetating clear-felled forests, and restoring coastal foredunes), it would be possible to reduce the impacts of natural hazards to a large degree. It also highlights the value of intact and well-managed landscapes and their role in reducing the probabilities and impacts of extreme climate events.</p></div

Flow duration curve for different scenarios of land cover and climate change.

<p>This shows the cumulative proportion of the months where a flow exceeded a given discharge for the different scenarios. The numbers prefixing the annotated description of each scenario provides a reference to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095942#pone-0095942-t001" target="_blank">Table 1</a>, which describes each scenario in more detail. Extreme low flows were defined as those with >90% exceedance, which were used in this study to represent severe drought conditions. A log-normal probability curve was used to allow the low and high flow ends of the plot to be more clearly displayed.</p

The location of the hazard model study areas within Eden.

<p>The inset showing the location of Eden in South Africa.</p

Wave run-up elevations for various storm-wave return intervals for different scenarios of beach slope and climate change.

<p>Simulations used here are for a typical sandy beach location in Eden (Tergniet, near Mossel Bay), which is prone to storm-wave damage. Return periods were based on the simulated wave run-up elevations for a south-south westerly swell, and spring high tide levels. The numbers prefixing the annotated description of each scenario provides a reference to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095942#pone-0095942-t001" target="_blank">Table 1</a>, which describes each scenario in more detail.</p

Flood return intervals for different scenarios of land cover and climate change.

<p>The numbers prefixing the annotated description of each scenario provides a reference to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095942#pone-0095942-t001" target="_blank">Table 1</a>, which describes each scenario in more detail. The changes in the values for each return interval illustrate the potential changes in the likelihood of extreme flow events under the different scenarios. For example, the return period of a flood with a daily flow of 150 mm (similar to the May 1981 flood in this area) would decrease from a baseline of more than 100 years to 70 years under future climate (scenario 5).</p