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In this paper, 245 studies were reviewed to understand approaches used for estimating river channel transmission losses. Findings indicate that regression equations, differential equations, flow ro...

Non-perennial rivers (NPRs) account for more than 50% of the world’s river network and their occurrence is expanding. Some rivers that were previously classified as perennial have evolved to be NPR...

An understanding of processes and factors accounting for spatiotemporal variations of baseflows is necessary for sustainable water resources management, particularly in semi-arid regions. Most of the southern part of the Western Cape Province of South Africa experiences a Mediterranean climate typified by long dry summers. Thus, baseflows of rivers draining areas with Table Mountain sandstones sustain water for humans and ecosystems. Processes and factors accounting for spatiotemporal variability of baseflows in these rivers are not adequately understood. This study aimed to determine the spatial and temporal variations of baseflows across streams in a mountainous region with Table Mountain Group. The study was done on three sub-catchments (1.0 to 2.5 km2) within the Jonkershoek Valley that drains the Hottentots Holland Mountains. A two-parameter recursive digital filtering method (RDF) was combined with the conductivity mass balance method (CMB) to separate baseflow from daily streamflows during the 1946-2019 period. The results of baseflow separation using the CMB method were used to calibrate the RDF parameter (BFImax). The results showed that annual baseflow contributions varied spatially and the temporal variations were minor. Baseflows contributed 38 to 86 % of the annual streamflows. This wide range was unexpected considering that the sub-catchments were adjacent to each other and with similar geology. The variations could be explained by rugged topography and spatial irregularity of fracturing. The results also showed seasonality in baseflow contributions. All three sub-catchments had as expected higher contributions from baseflow in the dry summer compared to wet winter. For Bosboukloof baseflows contribute 89% of summer flows and 82 % in winter, Tierkloof 73 % and 60 %, while these were 50% and 34 % for the Langrivier. Differences in topography and vegetation were considered to account for the spatial variations of baseflow contributions. For instance, Bosboukloof has the lowest slopes and most scree material and had the highest proportion of baseflow. The decreasing trend in monthly baseflow was noted during the driest months (Oct-Dec). This indicates the vulnerability of baseflow. Again, this was particularly the case for Bosboukloof, the site most fully afforested with pines that may tap into the deeper water sources.

The study sought to assess the impacts of land use and land cover (LULC) changes on two wetland systems (Makuleke and Nylsvley Nature Reserve) in the Limpopo Transfrontier River Basin (LTRB) in Sou...

The utilisation of drinking water supply systems for productive uses is not a new practice in Zimbabwe and the world over. This study sought to explore how multiple uses of water, in this case community gardening as a productive use combined with domestic uses influence sustainability of communally-managed rural water supply systems. Using the independent samples t-test, it was noted that community gardening positively influences sustainability. The test was done on institutional, technical, social and financial factors of sustainability. Results showed that there were statistically significant differences in sustainability performance between water points used for multiple uses and those used for domestic uses only. However, it was also noted that using drinking water sources for multiple uses increases the frequency of water use conflicts and water point breakdowns, which negatively impact on sustainability. This means that where water sources are used for multiple uses additional management skills and resources may be required for the water points to be sustained. The study concluded that using domestic water sources for productive purposes enhances sustainability of water supply facilities; however, consideration has to be given about the relative importance and scale of the type of productive activity to be implemented.

Hydrological monitoring networks do not adequately cover non-perennial rivers in most parts of Africa partly because river flows do not frequently occur on these rivers. However, in the arid and semi-arid regions flows occurring on these rivers are an important resource that have to be managed judiciously. The lack of data on magnitudes, timing and frequency of non-perennial river flows constrain sustainable management of their water resources. The availability of moderate resolution satellite data (e.g. Sentinel-2 Multispectral Instrument and Landsat 8 Operational Land Imager) offers an opportunity to monitor the surface water availability specifically changes in surface areas covered with water in pools along these rivers. In this study, we investigated the use of remote sensing data to detect and monitor changes of water surface areas of pools along three non-perennial rivers and one perennial river in the Western Cape, South Africa, from 2016 to 2017, using Landsat 8 and Sentinel-2 datasets. We assessed a range of image pre-processing and image classification techniques to determine the most suitable method for surface water identification and pool area estimation along the selected rivers. The following indices were used; Normalised Difference Water Index (NDWI), Modified NDWI (MNDWI), Normalised Difference Vegetation Index (NDVI), Automated Water Extraction Index for shadowed (AWEIsh), non-shadowed regions (AWEInsh), and the Multi-Band Water Index (MBWI). The NDWI computed from Sentinel-2 TOA reflectance datasets was found to be the most suitable index for mapping pools, with an overall accuracy ranging between 60 and 86%. This index was used successfully to establish the variations of surface areas of pools covered with water along the Breede, Nuwejaars, Tankwa and Touws Rivers during the 2016–2017 period. The temporal variations of pool areas could be explained as expected by changes of rainfall and potential evapotranspiration. Overall, the study demonstrated the feasibility of using moderate resolution datasets to monitor pool changes of areas covered with water in non-perennial rivers, which contributes to improved management of water resources particularly in arid and semi-arid environments.

Small seasonal wetlands are a distinctive feature of the semi-arid environments. Although these systems are small and ephemeral in nature, they provide habitats to aquatic flora and fauna, and play a critical role in sustaining livelihoods through the provision of ecological services. There is a great concern that these wetlands are not routinely monitored, which has contributed to their poor management. So far, scientific research strides have been noted in mapping and understanding the spatial coverage and ecohydrological dynamics of wetlands in semi-arid areas using broadband multispectral data. However, because of the sensing characteristics of these platforms, mapping and monitoring of small wetlands remains a challenge., 26 pages research paper

The detrimental impacts of invasive alien plants on ecosystems and water resources have raised concerns in arid and semi-arid countries like South Africa where the average precipitation is approximately 500 mm/yr, which is below the world average of around 860 mm/yr. Several studies have examined the effects of invasive alien plants such as the Australian Acacias on the water resources. However, few studies have quantified the differences in water use between hillslope and riparian Acacia longifolia invasions. A. longifolia is one of the aggressive invader species in South Africa even on hillslopes that contribute substantially to runoff generation. Therefore, the encroachment of invasive alien plants has the potential to reduce runoff, thereby adversely affecting the available water downstream. This paper aims to; 1) compare transpiration rates of A. longifolia growing on hillslopes and along riparian areas, 2) establish the key drivers for water use by this species, and 3) estimate the hydrological impacts of the invasions at the catchment scale in the Heuningnes catchment, in the Western Cape Province of South Africa. Transpiration by the trees was measured using the heat pulse velocity sap flow method. Automatic weather stations and soil moisture sensors were used to monitor weather and soil water content variations at each site. The results showed that, at the stand level the riparian A. longifolia transpired two times more water (∼596 mm/yr) than on the hillslope (∼242 mm/yr). During years with above average rainfall, the water use rates by the invasions was estimated to be ∼579 mm/yr on the hillslope and could be as much as ∼1348 mm/yr at the riparian site. Thus, the hypothesis that riparian trees use more water than invasions on non-riparian areas was accepted in this study. At the catchment scale (740 km2), the estimated water use by the invasions was 20.5 Mm3. Clearing of all the invasions in the study catchment is likely to make 17 Mm3/yr of water available. Hence the clearing of A. longifolia along the riparian corridors should be prioritised as this will lead to water savings at the catchment scale.

Climate change is expected to exacerbate current stresses on water resources resulting from population growth, economic factors and land use changes, impacting on the availability of water resources and the sustainability of local ecosystems. In southern Africa, changes in the intensity, frequency and duration of weather extremes have resulted in recurrent droughts, floods, tropical cyclones among other phenomena. For example, the El Nino-Southern Oscillation effect has intensified in the past four decades (1900–2010) resulting in increased frequency of floods and droughts in Southern Africa. Furthermore, the projected increase in the frequency of droughts is likely to reduce flows and water storage. On the other hand, some regions may experience an increase in the frequency and magnitude of extreme precipitation events associated with flooding (and extreme high flows). Countries like Mozambique, South Africa, Malawi and Zimbabwe are already experiencing recurrent floods and droughts. Projected increases in the frequencies and magnitudes of such events through to 2050, coupled with rising populations in the region, suggests that the vulnerability of weather-sensitive sectors, particularly water resources and agricultural production will increase. This will affect aquatic ecosystems, water supply, irrigation, leisure, and hydropower generation. The implications of these findings are as follows: (1) Water availability is likely to be compromised, (2) Water management measures are likely to be tightened. (3) Dependence on rain-fed agriculture is likely to increase food insecurity for most southern African countries as a result of reduced agricultural production. (4) Similarly, electricity generation is likely to be reduced due to increased droughts and enhanced evapotranspiration as a result of the high temperatures. It is thus concluded that southern Africa is deemed to be a particularly vulnerable region on the African continent, as multiple biophysical, political and socioeconomic stresses interact to heighten the region’s susceptibility to climate change and variability and constrain its adaptive capacity. Thus, there is need to increase resilience of ecosystems and communities in light of the anticipated changes in hydrological regimes and extreme events.

Ecosystem destruction has been given as the primary reason for implementing Sustainable Development Goal 15 (SDG 15). This chapter investigates the role of springs in securing rural livelihoods in the Save Catchment of Zimbabwe. It invokes SDG 15 in the debate on springs by examining rural community vulnerabilities regarding the management of spring water and other ecosystem services. Purposive sampling was utilised to select participants for the questionnaire survey and key informant interviews. In the study, springs were shown to be an important component of rural livelihoods. Access to spring waterscapes in the Save Catchment has led to an improved food security and income to rural households. However, climatic variability, weak institutional control and overutilisation have reduced the capacity for springs and their waterscapes to support sustainable livelihoods. The findings reveal that degradation of spring waterscapes is occurring and the productive capacity of springs is being diminished. In view of the multiple uses of the springs in the study area, appropriate management strategies need to be instituted if the goals of SDG 15 are to be achieved.

In the quest to address sustainability challenges in the rural water sector the Community Based Management (CBM) approach was adopted by many developing countries including Zimbabwe as the model for managing rural water facilities. CBM having principles embedded on equity, empowerment and effectiveness was expected to promote sustainability, however field evidence has shown that the variance between theory and practice in its implementation has contributed to its failure to deliver expected results. This study was done to investigate how CBM is being implemented in Zimbabwe. The specific objectives were to analyze how practices of different stakeholders in the rural water sector differ from their roles as stipulated in the CBM framework and to analyze how discrepancies between theory and practice in CBM implementation are influencing sustainability of water supply systems. The study also sought to investigate how trainings which are stipulated in the CBM framework are being done. Data was collected using Focus Group Discussions (FGDs), Key Informant Interviews (KIIs) and a Water Point Committee questionnaire. Pearson Chi square test was used to analyze quantitative data while the thematic approach was used to analyze qualitative data. Results showed that most WPCs were not performing their roles as outlined in the CBM framework. Since most rural water projects were funded by Non Governmental Organizations (NGOs) their strategies and objectives were taking precedence over CBM guidelines which negatively impacted on technical, social and institutional factors of sustainability. The project nature of NGO programmes which are budget and time bound also resulted in CBM principles not being applied as outlined. Rural District Councils (RDCs) were depending on NGOs to fund water supply activities. WPCs were diverging from their stipulated roles due to incapacitation in technical and managerial skills which negatively impacted on financial and technical sustainability factors. Chi square test results show that there is a significant association between capacity building and sustainability ((χ2 = 3.20, df = 2, p

Apple orchards have previously been bearing 60–80 t ha−1 at most. However in recent years yield has increased to more than 100 t ha−1. There is need to understand the water requirements of the high yielding orchards, given that high crop loads are associated with high water use rates. The aim of this study was to quantify the water requirements of young and mature unstressed apple orchards. We also assess the impact of climate variables on transpiration rates. Data was collected in 4 orchards in the Western Cape Province. The orchards comprised young non-bearing (p>0.05) in the sapflux density of the Golden Delicious and Cripp's Pink cultivars. This suggests that these two cultivars have similar water use characteristics. Mature orchards transpired between 6000 to 8000 m3 ha−1 season−1 while non-bearing orchards used between 2000 to 3000 m3 ha−1 season−1.

Cover crops are widely planted in orchards for a variety of reasons. These include suppressing soil erosion, nutrient cycling, phytosanitary purposes, general orchard aesthetics etc. However, there is need to balance these benefits against use of scarce resources such as water and nutrients. Currently no information exists on how different cover crop species use water in orchards and how they cope with drought stress. The aim of this study was therefore to compare the transpiration dynamics of various cover crop types in order to identify species with conservative water use rates. Studied species included: 1) two exotic legumes i.e. Lupine (Lupinus albus L.), and Common vetch (Vicia sativa), 2) three exotic grasses i.e. Tall fescue (Festuca arundinacea), Rye grass (Lolium perenne), and Kikuyu grass (Pennisetum clandestium) and; 3) grasses that are indigenous to sub-Saharan Africa i.e. African Lovegrass (Eragrostis capensis) and Rhodes grass (Chloris gayana). The crops were planted in pots under controlled greenhouse conditions. Transpiration rates were quantified using miniature stem heat balance sap flow gauges and by manual weighing. Drought stress was imposed by withholding irrigation at selected intervals and the responses were quantified through changes in the water relations of the plants. The study showed that exotic legumes had the highest daily water use which peaked at about 2.4 L per square metre of leaf area per day, followed by exotic grasses at 1.5–2.0 L/m2/d. The indigenous grasses used the least water ranging from 0.8 to 1.2 L/m2/d. The indigenous grasses largely displayed an isohydric response to drought stress by maintaining their leaf water status with increasing soil water deficit. The exotic species, on the other hand, showed risk taking behaviour (anisohydry) wherein both the transpiration and leaf water status decreased sharply as drought stress increased. Consequently, some exotic species failed to recover when stress was relieved. From a water use perspective, this study demonstrates that indigenous grass species are more appropriate as cover crops in South African orchards because of their low transpiration rates and the ability to cope with extended periods of water deficit.

Accurate and timely information on surface water quality and quantity is critical for various applications, including irrigation agriculture. In-field water quality and quantity data from unmanned aerial vehicle systems (UAVs) could be useful in closing spatial data gaps through the generation of near-real-time, fine resolution, spatially explicit information required for water resources accounting. This study assessed the progress, opportunities, and challenges in mapping and modelling water quality and quantity using data from UAVs. To achieve this research objective, a systematic review was adopted. The results show modest progress in the utility of UAVs, especially in the global south. This could be attributed, in part, to high costs, a lack of relevant skills, and the regulations associated with drone procurement and operational costs. The progress is further compounded by a general lack of research focusing on UAV application in water resources monitoring and assessment. More importantly, the lack of robust and reliable water quantity and quality data needed to parameterise models remains challenging. However, there are opportunities to advance scientific inquiry for water quality and quantity accounting by integrating UAV data and machine learning.

Accurate estimates of orchard evapotranspiration (ET) and its components are important for precise irrigation scheduling, irrigation system designs, and optimal on-farm water allocation particularly in water-limited environments. Direct measurements of ET remain costly, laborious and sometimes difficult to apply over heterogeneous surfaces such as crop fields. Therefore, accurate crop water-use models are required for on-farm precise water resources management. In this study, we adopted and improved the Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model developed by Fisher et al 2008 to estimate crop water use across different apple plants. Specifically, the model was developed to quantify the partitioning of apple orchard water use into beneficial (tree transpiration) and non-beneficial water use (orchard floor evaporation) as influenced by tree canopy cover. Data were collected in twelve orchards spread across key apple producing regions in the Western Cape Province of South Africa over three growing seasons (2014/15, 2015/16, 2016/17). Model ET estimates were tested against ET data measured; using the eddy covariance method and transpiration measured based on sap flow monitoring techniques. The results showed that the original Fisher PT-JPL model performed poorly in ET estimation across all the orchards under study. The model yielded lower R2, ranging from 0.02 to 0.64 and Nash-Sutcliffe Efficiency (NSE) from -10.93 to 0.20. Thus, we subsequently improved the model by incorporating soil moisture and vapour pressure deficit stress factors and by introducing a variable Priestley and Taylor coefficient ( α ). The modified PT-JPL model demonstrated an improvement in ET estimates. The root mean square of error (RMSE) of the estimated daily ET varied from ±0.60 mm/d to ±1.99 mm/d whereas the mean absolute error (MAE) varied from ±0.49 mm/d to ±1.91 mm/d, while the R2 varied from 0.54 to 0.75 in orchards with varying canopy cover. The findings of this work underscore the utility of the modified PT-JPL model for estimating ET and its components in apple orchards from planting until the trees reach full-bearing age.

Satellite-based remote sensing of soil water content (SWC) is a promising technology for hydrological applications to overcome large spatiotemporal variabilities of SWC. This study investigated the performance of the Advanced Scatterometer (ASCAT) soil moisture product on METOP satellite (~12.5 km and downscaled to ~1 km resolution), against ground measurements of SWC taken with a Hydrosense II probe along transects of 360?820 m on agricultural and natural land at locations in the Western Cape. The ASCAT products estimated fairly accurately seasonal trends of SWC; performance was better on lower slopes (R 2 = 0.66) and uniform vegetation. ASCAT 12.5 km performed better in estimating SWC than the downscaled product (average concordance coefficient = 0.60 and 0.39, and R 2 = 0.84 and 0.74, respectively). ASCAT 12.5 km was more responsive to rainfall events, whilst the downscaled product was more sensitive to vegetation characteristics (normalised difference vegetation index and land surface temperature). In situations with ground measurement networks and data availability constraints, remote sensing could be a feasible alternative to monitor SWC for hydrological applications at the meso-scale (regional scale). Fil: Moller, Jason. University of the Western Cape; Sudáfrica Fil: Jovanovic, Nebo. CSIR Natural Resources and the Environment; Sudáfrica. University of the Western Cape; Sudáfrica Fil: García, César Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Católica de Córdoba; Argentina Fil: Bugan, Richard D. H.. CSIR Natural Resources and the Environment; Sudáfrica Fil: Mazvimavi, Dominic. University of the Western Cape; Sudáfrica

Sustainability of point water facilities is a major development challenge in many rural settings of developing countries not sparing those in the Sub-Saharan Africa region. This study was done in Zimbabwe to investigate the factors influencing sustainability of rural water supply systems. A total of 399 water points were studied in Nyanga, Chivi and Gwanda districts. Data was collected using a questionnaire, observation checklist and key informant interview guide. Multi-Criteria analysis was used to assess the sustainability of water points and inferential statistical analysis such as Chi square tests and Analysis of Variance (ANOVA) were used to determine if there were significant differences on selected variables across districts and types of lifting devices used in the study area. The thematic approach was used to analyze qualitative data. Results show that most water points were not functional and only 17% across the districts were found to be sustainable. A fusion of social, technical, financial, environmental and institutional factors was found to be influencing sustainability. On technical factors the ANOVA results show that the type of lifting device fitted at a water point significantly influences sustainability (F = 37.4, p

Prosopis spp., (or Mesquite), is a desert adapted woody weed which has invaded large parts of arid and semi-arid regions. It has a characteristic deep tap root, and forms dense impenetrable thickets along river banks, flood plains, and seasonal water courses. Several studies have quantified the water use by Prosopis , but there is limited information on how this compares with that of co-occurring groundwater dependent indigenous tree species in the arid and semi-arid tropics. Consequently the effects of removing Prosopis on groundwater, where they co-occur with indigenous trees, are not known. This study quantified the incremental water use by Prosopis invasions compared with the indigenous deep rooted Vachellia karroo ( V. karroo ) trees that normally replace Prosopis once it has been cleared. The study was done in an arid catchment in the Northern Cape Province of South Africa. Stem sap flow dynamics, groundwater levels, and weather data were collected hourly over 15 months in the invaded catchment. Data collection continued for a further 11 months after Prosopis had been cleared to monitor the recovery of the ecosystem from the invasions. There was no significant difference (P = 0.116) in the sap flux density of the two species although Prosopis had a much thinner sapwood depth than V. karroo due to its ring porous wood anatomy. However, at the stand scale Prosopis transpired more than five times more water (∼544 mm y −1 ) than V. karroo (∼91 mm y −1 ) since there were six times more Prosopis than the indigenous species. The removal of Prosopis slowed down the rate of decline of the water table from a pre-clearing peak of ∼8.9–5.0 mm d −1 after alien plant removal. Tree transpiration was accurately predicted by a simple model that used aquifer properties and hourly changes in water table depths with a RMSE of ±0.22 mm d −1 before and ±0.32 mm d −1 after clearing Prosopis .

Knowledge on rangeland condition, productivity patterns and possible thresholds of potential concern, as well as the escalation of risks in the face of climate change and variability over savanna grasslands is essential for wildlife/livestock management purposes. The estimation of leaf area index (LAI) in tropical savanna ecosystems is therefore fundamental for the proper planning and management of this natural capital. In this study, we assess the spatio-temporal seasonal LAI dynamics (dry and wet seasons) as a proxy for rangeland condition and productivity in the Kruger National Park (KNP), South Africa. The 30 m Landsat 8 Operational Land Imager (OLI) spectral bands, derived vegetation indices and a non-parametric approach (i.e., random forest, RF) were used to assess dry and wet season LAI condition and variability in the KNP. The results showed that RF optimization enhanced the model performance in estimating LAI. Moderately high accuracies were observed for the dry season (R2 of 0.63–0.72 and average RMSE of 0.60 m2/m2) and wet season (0.62–0.63 and 0.79 m2/m2). Derived thematic maps demonstrated that the park had high LAI estimates during the wet season when compared to the dry season. On average, LAI estimates ranged between 3 and 7 m2/m2 during the wet season, whereas for the dry season most parts of the park had LAI estimates ranging between 0.00 and 3.5 m2/m2. The findings indicate that Kruger National Park had high levels of productivity during the wet season monitoring period. Overall, this work shows the unique potential of Landsat 8-derived metrics in assessing LAI as a proxy for tropical savanna rangelands productivity. The result is relevant for wildlife management and habitat assessment and monitoring.

This chapter examines how the availability and non-availability of river flows has affected benefits realized by communities residing along the Boteti River in Botswana. The Boteti River, which is about 350 km long, derives all its flows from outflows of the Okavango Delta and then discharges into the Makgadikgadi Pans. Peak outflows from the delta occur during the dry season, June to October, and during wet years such as from 1974 to 1982, water flows along the whole river from the delta to the Makgadikgadi Pans. Since 1991, outflows from the delta have only covered about 50 km, with the rest of the river being dry. There has been lack of flows on the downstream section in some years (e.g., 1929-39, 1941-47). Communities residing along the 50 km stretch that is annually flooded benefit from the river through livestock watering, flood recession crop cultivation, fishing, and harvesting of aquatic plants for food and construction. These benefits were not realized by those residing along the rest of the 300 km stretch that was not receiving flows from the delta during the 1991-2008 period.

Orchard evapotranspiration (ET) is a complex flux which has been the subject of many studies. It often includes transpiration from the trees, cover crops and weeds, evaporation from the soil, mulches and other orchard artefacts. In this study we investigated the contribution of the orchard floor evaporative fluxes to whole orchard ET focusing on the transpiration dynamics of understorey vegetation which is currently not well known. Data on the partitioning of ET into its constituent components were collected in apple (Malus Domestica Bork) orchards with varying fractional canopy cover. The study orchards were in the prime apple growing regions in South Africa. The orchards were planted to the Golden Delicious/Reinders and the red cultivars (i.e. Cripps’ Pink/ Royal Gala/Fuji). Tree transpiration was quantified using the heat ratio method and the thermal dissipation sap flow techniques. Understorey transpiration was measured at selected intervals using micro stem heat balance sap flow gauges calibrated against infrared gas analyser readings. Orchard ET was measured using an open path eddy covariance system while the microclimate, radiation interception, and soil evaporation were also monitored. Orchard floor evaporative fluxes accounted for as much as 80% of the measured ET in young orchards with dense understorey vegetation that covered most of the orchard floor. In these orchards the understorey transpiration was of the same order of magnitude as the bare moist soil evaporation suggesting that water use by the understorey vegetation was substantial. However, in mature orchards with a high canopy cover (>55% fractional cover), orchard floor water losses were less than 30% of the measured ET. Understorey transpiration rates were much lower, contributing less than 10% of the whole orchard ET. Significant volumes of water can be saved, especially in young orchards, by keeping the orchard floor vegetation short, reducing the area occupied by understorey vegetation, and by reducing the wetted ground surface area.

Water is one of the most essential natural resource that sustains livelihoods. Freshwater consumption and demand have, spiralled over the years, due to population growth, agricultural and industrial intensification. Innovative water conservation techniques (greywater reuse, rainwater harvesting, seawater desalination and ground water extraction, etc.), especially in the face of climate change and climate variability are central in minimizing water shortages, hunger and poverty alleviation, as well as health challenges. Most of water conservation methods remain ineffective and have less adoption, due to associated costs, inaccessibility and technical expertise in addressing water challenges, particularly in developing countries. Greywater reuse, which approximately represents 43–70% of the total domestic wastewater volume remains as the alternative and effective source of water that can help reduce pressure on freshwater for food production and poverty alleviation in third-world countries. Great research strides have been demonstrated on greywater reuse for agricultural use, but much remains unknown with regard to adoption rates, especially in developing countries. This work provides a detailed review on greywater reuse in crop production with particular emphasis on community perceptions, challenges and opportunities, lessons from other countries and possible implications on food security. The study has demonstrated that greywater reuse is a common practice in both developed and developing nations as a coping strategy. However, it was observed that some communities remain cautious and sceptic on its use for home gardening purpose. This resource is regarded as unclean and unfit for food crop irrigation. Limited adoption rates seem to be due to limited information or awareness programs and platforms on the potential of greywater reuse as supplement for freshwater, especially in developing countries like South Africa. However, strategies i.e. installation of greywater systems, incentivising greywater use have seen a rise in the adoption greywater in developed world. There is a need to find possible ways on how strategies from developed countries can be adopted in developing countries to promote greywater reuse for home gardening purposes.

In this study, we assess the quality of greywater for reuse in home gardens through irrigation in water-limited environments of the rural Limpopo province, South Africa. To address this objective, pH, Electrical Conductivity (EC), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+) and Sodium (Na+) were tested from the household sampled greywater e.g. kitchens, bath and laundry sampled. Hazards in greywater were determined using water quality indices and the derived results were assessed for any differences using ANOVA and Tukey method. The average pH values of study area 1 (STA1), study area 2 (STA2) and study area 3 (STA3) were found to be slightly alkaline (pH 8–9). Generally, most of the Sodium Adsorption Ratio (SAR) values where within the low category (1–10) indicating its acceptability for reuse. Most water quality parameters had high Soluble Sodium Percentage (SSP), with an average of 68.09%, 79.42% and 92.30% in STA1, STA2 and STA3, respectively. Further, the Kelley's Ratio (KR) indicate elevated levels of salt concentrations in greywater, with exceptions from laundry water in STA1. In contrary, residual chloride levels in all samples were found to be within the acceptable range (0–30meq/L) with

The FAO-56 crop coefficient (Kc) approach is widely used for making irrigation decisions. Allen and Pereira (2009) extended this approach by developing a method for estimating Kc using a density coefficient (Kd), which is estimated from the fraction of ground covered by vegetation and plant height. In this study we evaluated this method using detailed measurements of transpiration (T), evapotranspiration (ET), soil attributes, weather, and tree physiological variables in 12 apple (Malus domestica Borkh.) orchards in the Western Cape Province of South Africa. Mid-summer canopy cover of the orchards was less than 20 % in young non-bearing and exceeded 60 % in mature full-bearing orchards. Data were collected over three growing seasons (October 2014 to May 2017) in orchards planted to the Golden Delicious/Reinders®, Cripps Pink, Cripps Red, and Rosy Glow apple cultivars. The original Allen and Pereira (A&P) method significantly overestimated the basal crop coefficients (Kcb) by on average 47 % in mature and 103 % in young orchards, respectively. However, improved Kcb estimates were obtained by adjusting the ratio of the resistances (i.e. rl /100) in the A&P method, where rl is the mean leaf resistance and 100 s/m is the typical resistance for annual crops. We defined a resistance parameter “α” for apple orchards which is equivalent to the bulk canopy resistance of a well-watered tree. Replacing rl /100 with rl /α, and using the measured mean rl and other biophysical measurements to solve the A&P equation for α gave a value ∼ 37 s/m. The improved Kcb values were used to derive the orchard Kc taking into account the contribution of cover crops whose transpiration was measured using miniature stem heat balance sap flow gauges. The seasonal total transpiration (T) estimated as T = Kcb x ETo, where ETo is the reference ET closely matched the measured values with a RMSE (root of the mean square error) of ∼ ±16 mm. Therefore, using the mean canopy resistance which is representative of apple trees in the A&P method has the potential to accurately predict both the crop coefficients and water use of apple orchards from planting until full bearing age.

There is increasing concern in southern Africa about the possible decline of rainfall as a result of global warming. Some studies concluded that average rainfall in Zimbabwe had declined by 10% or 100 mm during the last 100 years. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for (a) the early part of the rainy season, October-November-December (OND), and (b) the mid to end of the rainy season, January-February-March (JFM) are analysed for the presence of trends using the Mann-Kendall test, and for the decline or increase during years with either high or low rainfall using quantile regression analysis. The Pettitt test has also been utilized to examine the possible existence of change or break-points in the rainfall time series. The analysis has been done for 40 rainfall stations with records starting during the 1892–1940 period and ending in 2000, and representative of all the rainfall regions. The Mann-Kendal test did not identify a significant trend at all the 40 stations, and therefore there is no proof that the average rainfall at each of these stations has changed. Quantile regression analysis revealed a decline in annual rainfall less than the tenth percentile at only one station, and increasing of rainfall greater than the ninetieth percentile at another station. All the other stations had no changes over time in both the low and high rainfall at the annual interval. Climate change effects are therefore not yet statistically significant within time series of total seasonal and annual rainfall in Zimbabwe. The general perception about declining rainfall is likely due to the presence of multidecadal variability characterized by bunching of years with above (e.g. 1951–1958, 1973–1980) and below (e.g. 1959–1972, 1982–1994 ) average rainfall.

Papyrus wetlands (dominated by the giant sedge Cyperus papyrus L.) occur throughout eastern, central and southern Africa and are important for biodiversity, for water quality and quantity regulation and for the livelihoods of millions of people. To draw attention to the importance of papyrus wetlands, a special session entitled “The ecology of livelihoods in papyrus wetlands” was organized at the 9th INTECOL Wetlands Conference in Orlando, Florida in June 2012. Papers from the session, combined with additional contributions, were collected in a special issue of Wetlands Ecology and Management. The current paper reviews ecological and hydrological characteristics of papyrus wetlands, summarizes their ecosystem services and sustainable use, provides an overview of papyrus research to date, and looks at policy development for papyrus wetlands. Based on this review, the paper provides a synthesis of research and policy priorities for papyrus wetlands and introduces the contributions in the special issue. Main conclusions are that (1) there is a need for better estimates of the area covered by papyrus wetlands. Limited evidence suggests that the loss of papyrus wetlands is rapid in some areas; (2) there is a need for a better understanding and modelling of the regulating services of papyrus wetlands to support trade-off analysis and improve economic valuation; (3) research on papyrus wetlands should include assessment of all ecosystem services (provisioning, regulating, habitat, cultural) so that trade-offs can be determined as the basis for sustainable management strategies (‘wise use’); (4) more research on the governance, institutional and socio-economic aspects of papyrus wetlands is needed to assist African governments in dealing with the challenges of conserving wetlands in the face of growing food security needs and climate change. The papers in the special issue address a number of these issues.

Using a political ecology framework, this article describes the main developmental challenges facing communities living within the Boteti River sub-basin of northwestern Botswana. The data derive primarily from household surveys conducted over several months in 2008. They show that residents within the study area face significant challenges from unstable supplies of potable water and a highly degraded physical landscape. The article suggests that new opportunities for improved livelihood security have arisen with the recent return of the river to a perennial condition. For more than two decades, only a small portion of the river has had significant surface flow, with the rest dry year round. Given the area's proximity to landscape-dependent, wildlife-based tourism activity, the article suggests that the shifting basin hydrology presents sport-for-development agents with numerous opportunities for meaningful development interventions. In elaborating on what Coalter calls ‘sport plus’ and’ plus spo...

Botswana is a semiarid country and yet has one of the world’s famous wetlands: the Okavango Delta. The Thamalakane-Boteti River is one of the Delta’s outlets. The water quality of the Thamalakane-Boteti River was determined and related to its utilisation. The major land uses along the Thamalakane River within Maun are residential areas, lodges, hotels, and grazing by cattle and donkeys. The water is used as a source of water for livestock, wildlife in a game park, horticulture and domestic applications including drinking. The river is also used for fishing. To check whether these activities negatively impact on the water quality, pH, electrical conductivity, dissolved oxygen, temperature, total dissolved nitrogen and phosphorus, Faecal coliforms and Faecal streptococci and selected metals were determined from July 2005 to January 2006. The pH was near neutral except for the southern most sampling sites where values of up to 10.3 were determined. Dissolved oxygen varied from 2 mg/l to 8 mg/l. Sodium (range 0.6–3.2 mg/l), K (0.3–3.6 mg/l), Fe (1.6–6.9 mg/l) conductivity (56–430 μS/cm) and Mg (0.2–6.7 mg/l) increased with increased distance from the Delta, whereas lead showed a slight decline. Total dissolved phosphorus was low (up to 0.02 mg/l) whereas total dissolved nitrogen was in the range 0.08–1.5 mg/l. Faecal coliform (range 0–48 CFU/100 ml) and Faecal streptococci (40–260 CFU/100 ml) were low for open waters with multiple uses. The results indicate that there is possibility of pollution with organic matter and nitrogen. It is recommended that more monitoring of water quality needs to be done and the sources of pollution identified.

There is a growing awareness and understanding of the need to allocate water along a river to maintain ecological processes that provide goods and services. Legislation in Zimbabwe requires water resources management plans to include the amount of water to be reserved for environmental purposes in each river basin. This paper aims to estimate the amount of water that should be reserved for environmental purposes in each of the 151 sub-basins or water management units of Zimbabwe. A desktop hydrological method is used to estimate the environmental flow requirement (EFR). The estimated EFRs decrease with increasing flow variability, and increase with the increasing contribution of base flows to total flows. The study has established that in order to maintain slightly modified to natural habitats along rivers, the EFR should be 30–60% of mean annual runoff (MAR) in regions with perennial rivers, while this is 20–30% in the dry parts of the country with rivers, which only flow during the wet season. The inclusion of EFRs in water resources management plans will not drastically change the proportion of the available water allocated to water permits, since the amount of water allocated to water permit holders is less than 50% of the MAR on 77% of the sub-basins in the country.

International audience; This review assesses the potential of the African continent to contribute to the three main targets of the new science decade of IAHS (Panta Rhei): understanding, estimation and prediction, and science in practice. The continent has an extremely diverse climate and physical environment, and is faced with many problems in the interaction between hydrology and society. While inadequate financial and institutional resources often constrain the pursuit of high-level scientific research, there is substantial hydrological research capacity within Africa. The topics covered over the past decade have partly anticipated some of the research themes adopted as part of the Panta Rhei initiative. African hydrological scientists should therefore be in a better position to make future contributions, largely because their research is already grounded in applications linked to societal needs. Some of the papers reviewed and included in the special issue of Hydrological Sciences Journal introduced in this paper reflect international partnerships, while others reflect emerging partnerships between institutions within Africa. Editor M Acreman

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.