Doctoral Degrees (Environmental Hydrology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6588

Browse

Now showing 1 - 20 of 30

An assessment of the potential impacts of climate variability on sugarcane production across Southern Africa.
(2023) Ngcobo, Simphiwe Innocent.; Jewitt, Graham Paul Wyndham.; Hill, Trevor Raymond.; Archer, Emma.
The scale and extent of changes to demographic, economic and environmental systems exacerbated by human activities have been rapid and pervasive enough that it has been established that a new geologic era termed the Anthropocene has already begun. One of the most critical and challenging consequences of the Anthropocene has been the accelerated release of greenhouse gases leading to global warming and, consequently, climate change (CC), which has impacted hydrological responses and available water resources by increasing surface temperatures and altering precipitation patterns across spatio-temporal scales. These changes have exacerbated the vulnerability of various systems that sustain livelihoods, placing them at high risk of collapse. One of these systems is sugarcane production, which is a crucially important agricultural activity in many parts of the world, including southern Africa. There is a consensus that as a region, southern Africa will be subjected to amplified hydrological impacts which will affect the sugarcane production landscape. Further the expansion and intensification of sugarcane production across southern Africa is highly likely due, in part, to the recognition of the economic and social importance of this activity for supporting livelihoods. Sugarcane yields have been declining over the past 25 years in the region because of the increased frequency of climatic extremes. Literature reviews showed that by amplifying precipitation variability, climate change will increase the exposure and vulnerability of sugarcane to water stress and will have a devastating impact on yields. However, knowledge gaps remain regarding climate change impacts on water resources and sugarcane yields. Further, few studies have addressed the vulnerability and adaptation potential of sugarcane production at sufficient spatio-temporal scales. To address these knowledge gaps, an initial review was conducted to understand the dynamics between global change and water resources across southern Africa. The review showed that although global drivers are intricately related, their water resources impacts are highly complex, indirectly coupled and spatially and temporally sensitive. Having established a general perspective of the impacts of global change in southern Africa, the multi-scale drivers of sugarcane production were analysed using of a frequency analysis. This approach allowed the determination of proximate and ultimate drivers in the uMngeni, uMlaas, and Umvoti catchments in South Africa, the Ubombo catchment in eSwatini, the Shire catchment in Malawi and the Kilombero catchment in Tanzania. The frequency analysis provided quantitative descriptions of the water resource impacts of sugarcane production across southern Africa. Applying a relationship between observed sugarcane yields and future low, medium, and high production scenarios, this study developed water use estimates for sugarcane over multiple growing cycles. Results indicated that ultimate drivers play the most dominant role in the expansion of sugarcane production within each catchment. Drawing from this analysis, a methodology of assessing yield declines was developed based on a yield gap analysis using the AquaCrop crop growth model. The results were used to develop recommendations to mitigate yield declines by offering safeguards for the sugarcane industry against climatic extremes. Modelling results suggested that yield trends can be attributed to existing crop management approaches instead of prevailing hydroclimatic regimes. The importance of recognising the vulnerability and adaptation potential in sugarcane production was highlighted in this study. It was concluded that if sugarcane growers are to adapt to the effects of extreme climatic events, they must consider shifting crop management approaches and be proactively included in related research. This research highlighted the importance of addressing the interactions between activities that drive land use change, such as sugarcane production, and the current impacts of climatic extremes on water resources. This is important in rapidly developing regions and climate change hotspots such as southern Africa. The development of innovative adaptation policies that will safeguard the already-pressured water resources and secure the sustainability of sugarcane production will become increasingly important under an altered climate.
Development and assessment of an integrated largescale hydrological modelling tool for water resources management in the Cauvery Catchment, India.
(2022) Horan, Robyn.; Smithers, Jeffrey Colin.; Kjeldsen, Thomas Rodding.; Clark, David John.; Toucher, Michele Lynn.
Economic development and population growth in southern India have resulted in rapid changes to land use, land management and water demand, significantly impacting and degrading water resources. The significant anthropogenic influences across the catchment have contributed to changes in hydrological functioning. Focussing on the highly contentious inter-state Cauvery River Catchment, this study aims to address the key scientific challenges faced within this catchment. The study was designed to develop an integrated large-scale hydrological model to improve water resource assessments in a highly heterogeneous and data-scarce region whilst considering the primary water resource challenges facing the Cauvery Catchment. The Upper Cauvery region, located in the Western Ghats, acts as the water tower of the catchment. The rainfall in the region is monsoonal, the topography is complex, and the rain gauge network is sparse, resulting in the estimation of rainfall being particularly challenging. The scarce rainfall data available in the Western Ghats region is hindering the understanding of the regional weather system, and the accepted rainfall dataset for India, Indian Meteorological Department rainfall grids, are known to have inaccurate estimations within the Western Ghats. The current knowledge of the meteorology and hydrology of the Upper Cauvery is limited. Additionally, the anthropogenic impact on local hydrological processes, such as streamflow, groundwater recharge and evapotranspiration, is poorly constrained. The current understanding of how these diverse local changes cumulatively impact water availability at the broader catchment scale is minimal. Small-scale rural water management and urban heterogeneity may strongly affect water resource availability across southern India. However, how such fine-scale factors propagate to the river catchment is largely unclear. The Global Water Availability Assessment (GWAVA) model was applied initially to the Upper Cauvery region to determine the suitability and compare model results from other modelling tools applied in the region. Two new versions of the GWAVA model were then developed. The first aimed to include small-scale runoff harvesting interventions (SSRHIs) into the model and quantify their impact on catchment water resources to address a renewed scientific interest in assessing their effectiveness in improving local water resources and the effects at a catchment scale. The second aimed to enhance the representation of groundwater and large operational dams whilst maintaining the model’s applicability to regions with low-data availability. The Indian Meteorological Department (IMD) gridded rainfall was compared to available gauges and selected remotely sensed datasets within the Upper Cauvery region. GWAVA will be utilised to assess the applicability of the remotely sensed data for a catchment rainfall estimation. GWAVA was determined to be a suitable tool to represent the Cauvery Catchment; however, the importance of an accurate spatial representation of rainfall for input into hydrological models and that comprehensive dam functionality is paramount to obtaining good results in this region was highlighted. Furthermore, the average GWAVA, VIC and SWAT ensemble provided a better predictive ability in catchments with dams than the individual models. The average ensemble offset uncertainty in input data and poor dam operation functionality within individual models. The inclusion of SSRHIs demonstrated that farm bunds appear to have a negligible effect on the average annual simulated streamflow. In contrast, tanks and check dams have a more significant and time-varying impact. The open water surface of the SSRHIs contributed to an increase in evaporation losses across the sub-catchment. The change in simulated groundwater storage with the inclusion of SSRHIs was not as significant as sub-catchmentscale literature, and field studies suggest. Including groundwater processes into GWAVA improved streamflow simulation in the headwater sub-catchments and the representation of the baseflow component such that low-flow model skill increased approximately 33-67% in the Cauvery and 66-100% in the Narmada. The existing dam routine was extended to account for large, regulated dams with two calibratable parameters. The routine improved streamflow simulation in sub-catchments downstream of major dams, where the streamflow was largely reflective of dam releases. The model performance was improved between 15 and 30% in the Cauvery and 7-30% in the Narmada when the regulated dams were considered. The model provides a more robust representation of the annual outflow volume from major dams, reducing the average bias from -17% to -1% in the Cauvery and from 14% to 3% in the Narmada. The daily dam releases were significantly improved in the Cauvery, approximately 26-164%. The improvement of the groundwater and dam routines in GWAVA proved successful in improving the overall model performance, the low-flow model skill and bias, and the inclusions allowed for improved traceability of simulated water balance components. It was found that the IMD rainfall within the high-altitude regions of the Western Ghats is underestimated, resulting in the under-simulation of streamflow in the Upper Cauvery. CHIRPS 0.25- and 0.05- degree, MSWEP and PERSIANN remotely sensed rainfall datasets were applied within this region. None of the individual rainfall datasets provided a more accurate representation of the rainfall than the commonly utilised IMD grids. However, using an ensemble of remotely sensed rainfall datasets, primarily the average ensemble, improved the accuracy of rainfall estimation in the catchment. The ‘off-the-shelf’ remotely sensed rainfall products provided a high variation in performance against the in-situ rain gauge data. The IMD grids provided the most accurate representation of rainfall compared to the individual remotely sensed rainfall datasets, despite underestimating the rainfall depths at high altitudes. In the case of the Upper Cauvery, the average ensemble provided a more accurate representation of the rainfall. An integrated large-scale hydrological model was developed to improve water resources assessments in a highly heterogeneous and data-scarce region whilst considering the major water resource challenges facing the Cauvery Catchment. The effects of runoff harvesting interventions, accounting for hard-rock aquifer groundwater processes and the impact of major dams were represented. The inclusion of these features improved the model performance throughout the Cauvery Catchment.
Influence of land cover degradation on the water balance of the Northern Drakensberg high altitude mesic grasslands, South Africa.
(2022) Gray, Byron Andrew.; Toucher, Michele Lynn.; Clulow, Alistair David.; Savage, Michael John.
Mountainous regions provide vital ecosystem services, such as water provisions to low land areas. However, these regions are also considered sensitive to the effects of environmental change, due to their high levels of endemism and biodiversity. Thus, environmental change within these regions could have significant consequences beyond the extent of the region itself. An important implication of environmental change is the impact a change in land cover could have on the water balance of a catchment, especially within the headwater catchments. The Drakensberg mountains in South Africa, is such a mountain region, which is vital for its provision of ecosystem services and generation of water resources. This mountainous region is under threat from anthropogenic environmental change. The Drakensberg mountain range has been identified within South Africa as a strategic water source area (SWSA) and within the Northern-Drakensberg SWSA exists the Maloti-Drakensberg Park, which is a protected area managed by Ezemvelo KZN Wildlife and a World Heritage site. The Northern-Drakensberg mountain range natural grasslands are under threat from two forms of land cover change degradation, that of woody encroachment and following disturbance, invasion of bracken fern. Woody encroachment occurs within the natural grasslands following the removal of fire, which is of concern within the protected areas, where fire is a current management tool to maintain the natural grassland cover. Outside the protected area, disturbances due to human activities such as overgrazing and poor land management have led to a substantial level of degradation occurring, providing ideal conditions for the invasion of bracken fern. To safeguard and maintain the assurance of supply from an important SWSA of South Africa, there is the need for improved understanding on the impacts of land cover change and degradation within the Northern-Drakensberg mountain range on the water balance of the region. Thus, the overall aim of this thesis is to understand the influence of land cover change related degradation on the water balance of the Northern-Drakensberg high-altitude mesic grasslands and what this in turn means for the water supply generated from this SWSA of South Africa. To achieve the main aim, the research was scaled from a point measurement to a basin scale where management decisions are made. To improve our understanding of the impact of degradation related land cover change on the water balance an observational approach is required. Located within the Maloti-Drakensberg Park is the long-term Cathedral Peak research catchments which provided the platform for the observation component of this research. Of interest in the Cathedral Peak research catchments were three hydrologically individual catchments. Catchment III which consists of a degraded bracken fern land cover following the historical research experiments within the catchment on the impacts of commercial Pinus patula plantation on streamflow. Despite rehabilitation efforts following the removal of the plantation, the catchment transitioned to a degraded state and is currently near-completely invaded with bracken fern. Catchment VI which is under natural grassland condition, is managed with a bi-annual spring burn as proven best practice within the Drakensberg region. This catchment formed the baseline catchment for this research. Catchment IX is a woody encroached land cover following the protection of fire since the 1950s as part of research into the implications of removing fire from the natural grasslands. These three catchments provided the ideal platform from which the change in water balance components under each land cover could be monitored and investigated. The process of evapotranspiration (ET), which forms the connection between the energy and water balances, is well understood to be one of the most affected components of the water balance following a change of land cover. Therefore, ET was the focus of the initial point observation research. Due to the cost and stringency of the prominent method for ET measurement of eddy covariance (EC), an alternative more financially feasible method of surface renewal (SR) was tested over both Leucosidea sericea (woody) and Pteridium aquilinum (bracken) vegetation in comparison to EC. It was determined that the SR method, and in particular the SR dissipation theory (SRDT) method, which is independent of EC, was the best alternative and cheapest method to EC. The SR method is now used within the Cathedral Peak research catchments for long-term estimations of ET over both vegetation canopies. During this research, calibration factors (α) for the surface renewal 1 (SR1) method were determined for both the Leucosidea sericea (woody) and Pteridium aquilinum (bracken) vegetation types for winter and summer. Having confirmed the SRDT ability as an alternative to EC, the seasonal ET of Leucosidea sericea (woody) and Pteridium aquilinum (bracken) was determined. Providing first insight into the seasonality of ET over these vegetation types. Both vegetations followed a similar seasonal ET cycle to the natural grasslands, with the largest difference occurring in winter when the grasslands become dormant. It was also found that the energy balance was altered under the degraded land covers, with both forms increasing available energy and latent heat flux. Following the understanding of the seasonal change in ET through point measurements, the research focus was scaled up to the research catchment. A comparison of catchment VI and IX was conducted to identify changes in the headwater catchment water balance between the natural grassland and woody encroachment land covers. Long-term data sets of precipitation and streamflow from the Cathedral Peak research catchments, in combination with the seasonal ET observations showed that over time, as woody encroachment increased, the catchment rainfall:runoff response ratio decreased, as did streamflow under woody encroachment compared to natural grassland. Having gained an understanding of the impacts on a water balance of a headwater catchment, hydrological modelling in combination with scenario analysis was used to understand the impacts on water supply from the upper-uThukela catchment were both land cover degradation threats left unmanaged. Land cover parameters were unavailable for Leucosidea sericea (woody) and Pteridium aquilinum (bracken), and therefore were derived from understanding gained during observation. The ACRU agrohydrological model was utilised and confirmed to simulate current land cover conditions within the upper-uThukela satisfactorily at both the headwater and catchment levels. It was identified that both forms of land cover change resulted in a reduction in streamflow. This was largest for woody encroachment. The most affected flows were the low flows and winter dry period flows. Headwater catchments were also identified as the most impacted by land cover change. The key conclusions of the research were: • that the surface renewal methodology is a viable alternative for obtaining estimates of evapotranspiration over indigenous vegetation types; • that the energy balance and ET of woody vegetation in comparison to the natural grassland was significantly altered; • the importance of fire, as not only a management tool for the maintenance of the natural grasslands, but also to ensure the sustainability of the vital water resources and ensuring water security; • that there is an evident lag between the onset of degradation in the form of woody encroachment and the resultant impacts on streamflow; • the disproportionally large impact degradation related land cover change within these headwater catchments has on the downstream water balance relative to low land catchments. Following the analysis and with the understanding gained, it is recommended that the natural grasslands continue to be managed using fire, and continued protection of the natural grasslands needs to be maintained. Observation within these headwaters is key to improving the understanding of change and to drive decision making, allowing for the optimal management of the important SWSA.
Detection and early warning of lightning and extreme storm events in KwaZulu-Natal, South Africa.
(2020) Mahomed, Maqsooda.; Clulow, Alistair David.; Mabhaudhi, Tafadzwanashe.; Savage, Michael John.; Chetty, Kershani Tinisha.; Strydom, Sheldon.
Abstract available in pdf.
Effects of soil carbon and ambient carbon dioxide concentrations on hydrological processes: a modelling study.
(2020) Schütte, Stefanie.; Schulze, Roland Edgar.; Scholes, Mary.
Abstract available in PDF.
Development and assessment of an improved continuous simulation modelling system for design flood estimation in South Africa using the ACRU model.
(2019) Rowe, Thomas James.; Smithers, Jeffrey Colin.; Clark, David John.
An estimate of the risk associated with flood events is required to adequately design hydraulic structures and limit negative socio-economic impacts as a result of floods. The methods used to estimate design floods in South Africa are outdated and are in need of revision. A National Flood Studies Programme (NFSP) has recently been initiated by Smithers et al. (2016) to overhaul Design Flood Estimation (DFE) procedures in South Africa. One of the recommendations of the NFSP is development and assessment of a Continuous Simulation Modelling (CSM) approach to DFE. Consequently, the aim of this study is to further develop and assess the performance of an improved comprehensive CSM system, to consistently and reliably estimate design flood discharges in small catchments (0 - 100 km2) in South Africa using the ACRU model. In the development of the approach a strong emphasis has been placed on ease of use from a practitioner’s point of view. The aim is achieved through several specific objectives as summarised below. The first objective was to review CSM approaches applied locally and internationally for DFE, in order to identify research gaps and guide the development of an improved national CSM system for DFE in South Africa. The review culminates with a list of recommendations and steps required to develop and adopt a CSM approach for DFE in practice. The first critical step identified and required was the development of a comprehensive CSM system using the ACRU model (Schulze, 1995). This included: the structure of the system and how to implement the system, an enhanced land cover and soils classification to apply with the system and default input information and databases to use with the system. The second objective addresses the recommendations made from the literature review, where a comprehensive CSM system for DFE using the ACRU model is developed and described in detail. Based on similarities identified between the ACRU (Schulze, 1995) and SCS-SA models (Schmidt and Schulze, 1987a), as well as the fact that the SCS-SA model is relatively simple and widely applied in practice, the CSM system was adapted to be consistent with the land cover classification used in the SCS-SA model. This included the incorporation of a methodology and rules, developed by Rowe (2015), to represent land management practices and hydrological conditions within the ACRU model. The development of this comprehensive CSM system with default national scale inputs and land cover classifications contributes to new knowledge on how to package a CSM system for DFE in South Africa. The third objective focuses on the assessment and verification of the CSM system developed, using observed data. Through the verifications and assessments performed an inconsistency between daily simulated stormflow volumes and the volume of stormflow used in the daily stormflow peak discharge equation was identified. Therefore, a revision, which is more conceptually correct than the current assumption that all stormflow generated from an event contributes to the peak discharge on the day, was applied to the fraction of the simulated daily stormflow used in the peak discharge equation. This corrected the inconsistency and significantly improved the results, thereby providing an improved methodology to more accurately estimate peak discharges in the ACRU model than had hitherto been the case. Despite the improvement in the results, a general over-simulation of peak discharges was still evident. Consequently, further investigation of the ACRU stormflow peak discharge computations was performed in order to identify which approach provides the most satisfactory results (Objective 4). This included a performance assessment of both the SCS single Unit Hydrograph (UH) approach and the incremental UH approach. The performance of each approach was assessed using both estimated parameters and parameters derived from observed data. These parameters include stormflow volumes, catchment lag times, and the distribution of daily rainfall, where applicable, to each approach. Comparison of the results from the two approaches indicated that more accurate results are obtained when applying the incremental UH approach, when using both estimated or observed parameter inputs. In terms of the incremental UH approach, it was identified that the approach is more sensitive to the use of synthetic daily rainfall distributions compared to estimated lag times. Based on the results obtained new knowledge and additional research gaps related to: (i) improved estimation of the distribution of daily rainfall within the ACRU model, (ii) links between the distribution of daily rainfall and catchment lag time, and (iii) the need to further verify and possibly recalibrate CNs for South Africa were identified. The fifth objective addressed is an assessment of the impact of model configuration on the performance of the ACRU CSM system developed, in order to propose a final CSM system for DFE in South Africa. Results when using site-specific land cover and soils information are compared to those obtained when different sources of input information are used, such as the national land cover and soils maps developed for the entire country. The results when using these default national datasets were not particularly good, however recommendations are made to improve on the results. In addition, the most appropriate current databases to use with the CSM system are defined, providing users with the most appropriate default information currently available to use in the absence of site-specific information. The last objective addressed was a comparison of the performance of the final ACRU CSM system proposed in this study to that of the widely applied SCS-SA model and associated approaches, when using the same input information. Ultimately, the final ACRU CSM system proposed provides results that are superior to those from the SCS-SA model and associated approaches. In addition, several advantages of the ACRU CSM system over the traditional SCS-SA approaches were identified. Recommendations were, however, made to improve on the CSM system developed in this study and to use the results to update the SCS-SA model. New knowledge on the performance of the SCS-SA model and its associated approaches compared to that of the comprehensive CSM system developed for South Africa is therefore provided in this study.
Degradation of ecological infrastructure and its rehabilitation for improved water security.
(2018) Hughes, Catherine Jane.; Jewitt, Graham Paul Wyndham.
Abstract available in PDF file.
Water-use dynamics of alien plant invaded riparian forests in South Africa.
(2018) Scott-Shaw, Bruce Charles.; Everson, Colin Stuart.
In South Africa the invasion of riparian forests by alien trees has the potential to affect the country’s limited water resources. It is difficult for government initiatives, such as the Working for Water (WfW) alien clearing programmes, to justify alien tree removal and implement rehabilitation unless a known hydrological benefit can be seen. Consequently water-use within riparian forests at three climate diverse research catchments within South Africa were monitored using the heat ratio method. The use of the Soil Water Assessment Tool (SWAT) and a Sequential Uncertainty Fitting (SUFI-2) algorithm allowed for the auto-calibration of the SWAT model at each research site using measured water-use data. Within the winter rainfall region of the Western Cape the alien stand used nearly six times more water per unit area than the indigenous stand annually. The combined accumulated daily sap flow over a two year period for three Vepris lanceolata and three Acacia mearnsii trees was 36 000 L and 55 700 L respectively, clearly demonstrating the higher water-use of the alien A. mearnsii trees. In contrast, the water-use of alien species within the summer rainfall region of KwaZulu-Natal was double that of the indigenous species. The accumulated seasonal water-use was the least in the indigenous Searsia (~2 100 L), moderate in the indigenous Maytenus (~7 100 L) and high in the alien A. mearnsii (~15 900 L) trees. The spatial distribution of water-use within northern Zululand showed that the commercial forestry areas were the dominant water-users in the catchment. These findings indicate that there would be a hydrological gain if the alien species are removed from riparian forests and rehabilitated back to their natural state. The use of the SWAT model provided substantial insights into the spatial distribution of total evaporation (ET) throughout the selected catchment areas and is a suitable hydrological model for examining the impacts of different land-uses in catchments in South Africa. Given the quantified hydrological benefit, indigenous trees should be promoted for use in rehabilitation programmes where the natural vegetation is or was forests. This is especially relevant in light of South Africa’s limited water resources.
Development of a small-scale in-field integrated postharvest citrus treatment unit.
(2016) Kassim, Alaika.; Workneh, Tilahun Seyoum.; Laing, Mark Delmege.
Abstract available in PDF file.
Estimation of catchment response time in medium to large catchment in South Africa.
Gericke, Ockert Jacobus.; Smithers, Jeffrey Colin.
Abstract and extended abstract available in the print copy.
Quantification of the water-use dynamics of the dominant plant communities of the Eastern Shores in the iSimangaliso Wetland Park for improved water resource management.
(2015) Clulow, Alistair David.; Everson, Colin Stuart.; Price, Jonathan.; Jewitt, Graham Paul Wyndham.
No abstract available.
Mainstreaming adaptation to climate change into decision making in the water sector : concepts and case studies from South Africa.
(2015) Stuart-Hill, Sabine Ingrid.; Pahl-Wostl, Claudia.; Schulze, Roland Edgar.
Abstract available in Pdf file.
Ground and satellite-based assessment of hydrological responses to land cover change in the Kilombero River Basin, Tanzania.
(2013) Munishi-Kongo, Subira.; Jewitt, Graham Paul Wyndham.
Changes in land use and land cover are a global issue of concern, especially with regard to possible impacts on biophysical processes which affect the hydrological functioning of a system. Tanzania is no exception to this concern. This study, therefore, addresses the implications of land use alterations on the hydrodynamics of the Kilombero River Basin, specifically with regard to the Kilombero Valley’s wetlands and water resources, which have been altered and exploited to a great extent. As its starting point, the study embarked on mapping the current land cover in the Kilombero Basin and the quantification of the historical changes. The study revealed significant changes and, in recent years, increased rates of clearing natural vegetation cover and conversion to agricultural land. The most affected area of the Basin was the Kilombero Valley, a Ramsar Site and formerly extensively inhabited by wildlife, but which now has 62% of its area converted into agricultural and/or human settlements. In line with this observation, the study used two approaches for the impact analysis, a regional scale and a local scale approach. Plant physiology, soil moisture and micro-meteorological measurements were undertaken to quantify the impact of land cover change at local scale. Sensing techniques were then applied to assess the spatial extent of the changes and the basin scale (regional) impact thereof. Investigation of hydrological processes at a local scale placed emphasis on the implications of forest conversion from indigenous Miombo woodland to exotic Teak (Tectona grandis) forests. Field measurements showed the distinctive nature of Teak trees consumptive water use, both in quantity as well as in regard to the seasonal variation as compared to the native Miombo woodland forests. Teak was found to have higher transpiration rates, both during the rainy season (where the rates were approximately 10-fold higher than that of Miombo) and the period immediately after the cessation of rainfall, with consumptive water use rates being four-fold higher than that of Miombo. This contrast in water use was further observed in the measured soil water fluxes which evidenced a large difference in the components of the soil water balance. Less recharge was observed in the Teak forests suggesting significant impacts on the replenishment of groundwater resources in the study area. Assessment of the basin scale impacts of the land cover changes on the evapotranspiration (ET) regime was undertaken using the Surface Energy Balance System (SEBS) remote sensing model. Validation was provided by the Teak field sites and through the monitoring of ET from sugar cane using a Large Aperture Scintillometer (LAS). Results suggest a decrease in ET during the dry season. There is a clear transition of ET that follows the land cover transition from the natural and more adaptable vegetation, to rain-fed dependent crops and bare lands, where minimal ET is observed during the dry season. Similar seasonal leafing, and therefore a similar ET pattern, is observed with the conversion of natural forests to deciduous plantation forests. Irrigated crops, on the other hand, were found to have persistently higher ET throughout the year regardless of rainfall variability. This implies that land cover change in the Kilombera Valley is resulting in higher water use and less recharge in the wet season and a correspondingly lower ET (and possibly lower river flow) in the dry season than would occur under natural conditions. This research provides valuable information relevant to all stakeholders in the Kilombero River Basin (i.e. both smallholders and commercial sugarcane farmers, the forestry industry, Basin Water Authorities etc.). This information will help to inform decision-making around the sustainable management of the water resources in the Kilombero Valley for food security as well as for sustaining livelihoods and ecosystems.
Transient pressure waves in hillslopes.
(2013) Waswa, George W.; Lorentz, Simon Antony.; Le Roux, Pieter A. L.
Previous studies found that during a rainfall event, pre-event water, which exists in the catchment before the event, may appear in significant amounts in the stream stormflow hydrograph. Pre-event water is predominantly groundwater. Among the mechanisms that have been proposed to explain the rapid mobilization of pre-event water from hillslopes are: (1) groundwater ridging (GWR) i.e. the rapid rise of a water table in environments, where the capillary fringe, or the zone of tension saturation, is very close to the ground surface and (2) the Lisse Effect (LE) i.e. the rapid response of a groundwater level to pressurized pore air in the unsaturated zone. Published literature explains that GWR is caused by the application of a small amount of water on the ground surface. On the LE, it is explained that pressurized pore air acts at the water table, resulting in a rapid rise of the water level in a well, screened below the water table. These explanations are insufficient on the physical processes involved in GWR and the LE. The objectives of this study were: (1) to use the commonly observed catchment hydrological processes i.e. tensiometric pore water pressure, shallow groundwater levels, rainfall data and the hydraulic properties of soils, to quantify and describe the physical processes involved in GWR and the LE mechanisms; (2) to perform laboratory experiments, in order to understand the physical processes involved in the LE; and (3) to develop a mathematical theory that can describe the physical processes in the LE. Results indicated that GWR and the LE are caused by the addition (elevation) of potential energy in water within the capillary fringe. In GWR, the additional energy is from the intense rainfall. In the LE, the additional energy is from compressed pore air in the unsaturated zone. In both mechanisms, the added energy diffuses through the capillary fringe, as a downward pressure wave, releasing the tension forces in water. As soon as the downward pressure wave-front arrives at the water table, the water table begins to ascend, as an upward pressure wave. The ascending water table steepens the hydraulic gradient, which results in the rapid groundwater fluxes, without the recharge of the water table by the infiltration profile.
Challenges in modelling hydrological responses to impacts and interactions of land use and climate change.
(2012) Warburton, Michele Lynn.; Schulze, Roland Edgar.; Jewitt, Graham Paul Wyndham.
To meet society’s needs for water, food, fuel and fibre the natural land cover throughout the world has been extensively altered. These alterations have impacted on hydrological responses and thus on available water resources, as the hydrological responses of a catchment are dependent upon, and sensitive to, changes in the land use. Similarly, changes in the climate through enhanced carbon dioxide (CO2) levels in the atmosphere have resulted in increased temperature and altered precipitation patterns that alter hydrological responses. In combination, land use change and global climate change form a complex and interactive system, whereby both human influences and climate change manipulate land use patterns, and changes in land uses feed back to influence the climate system, with both impacting on hydrological responses. Relatively few studies have been undertaken examining the combined impacts of climate change and land use change on water resources, with no consensus emerging as yet as to combined influence of land use change and climate change on hydrological responses and the role of geographical characteristics in determining the overriding influence. There is, however, agreement that the effect on hydrological responses will be amplified. Given that South Africa is currently water stressed and considered to be highly exposed to climate change impacts, an understanding of hydrological responses to the complex interactions between land use and climate change is crucial to allow for improved integration of land use planning in conjunction with climate change adaptation into water resources management. To determine the sensitivity of land use to changing climate, a sensitivity study assessing the potential impacts of climate change on the areas climatically suitable for key plantation forestry species was undertaken. Under sensitivity scenarios of climate change the climatically optimum areas for specific forest species were shown to shift, with optimum areas changing in extent and location between and within South Africa’s provinces. With potential for shifts in land use due to climate change shown, the imperative to improve understanding of the dynamics between land use and climate change as well as the subsequent impacts on hydrological responses was further established. For the assessment of climate-land use-water interactions, a process-based hydrological model, sensitive to land use and climate, and changes thereof, viz. the daily time step ACRU model was selected. In order to increase the confidence in results from the model in a study such as this, its representation of reality was confirmed by comparing simulated streamflow output against observations across a range of climatic conditions and land uses. This comparison was undertaken in the three diverse South African catchments chosen for the study, viz. the semi-arid, sub-tropical Luvuvhu catchment in the north of the country, which has a large proportion of subsistence agriculture and informal residential areas, the Upper Breede catchment in the winter rainfall regions of the south, where the primary land uses are commercial orchards and vineyards, and the sub-humid Mgeni catchment along the eastern seaboard, where plantation forestry is dominant in the upper reaches, commercial plantation sugarcane and urban areas in the middle reaches, and urban areas dominate the lower reaches. Thus, in effect a space for time study was undertaken, thereby reducing the uncertainty of the model’s ability to cope with the projected future climate scenarios. Overall the ACRU model was able to represent the high, low and total flows, and thus it was concluded that the model could be used with confidence to simulate the streamflows of the three selected catchments and was able to represent the hydrological responses from the range of climates and diversity of land uses present within the catchments. With the suitability of the model established for the theme of this research, the understanding of the complex interactions between hydrological responses and land use could be improved. The hydrological responses of the three selected catchments to land use change were varied. Results showed that the location of specific land uses within a catchment plays an important role in the response of the streamflow of the catchment to that land use change. Furthermore, it was shown that the contributions of different land uses to the streamflow generated from a catchment are not proportional to the relative area of those land uses, and the relative contribution of the land use to the catchment streamflow varies with the annual rainfall of the catchment. With an improved understanding of the dynamics between land uses and hydrological responses, the impacts of climate change on hydrological responses were assessed prior to analysing the combined impacts on land use and climate change. Five plausible climate projections from three coupled atmosphere-ocean global climate models covering three SRES emissions scenarios which were downscaled with the RCA3 regional climate model and adjusted using the distribution-based scaling (DBS) approach for bias correction were used as climate input to the ACRU model, with future projections applied to a baseline land cover scenario compared to historical climate applied to the same baseline land cover scenario. No consistent direction of change in the streamflow responses was evident in the Mgeni and Luvuvhu catchments. However, decreases in streamflow responses were evident for all five scenarios for the Upper Breede. With an understanding of the separate impacts of land use and climate change on hydrological responses, an analysis of the combined impacts was undertaken to determine which changes were projected to be of greater importance in different geographical locations. Results indicated that the drier the climate becomes, the relatively more significant the role of land use becomes, as its impact becomes relatively greater. The impacts of combined land use and climate change on the catchments’ streamflow responses varied across both the temporal and spatial scales, with the nature of the land use and the magnitude of the projected climate change having significant impacts on the streamflow responses. From the research undertaken, the key results were • that the climatic variable to which plantation forestry species are most sensitive is rainfall; • that optimum growth areas for plantation forestry are projected to shift under changing climates, having a potentially significant impact on the landscape and thus on the hydrological responses from the landscape; • that the daily time-step, physical-conceptual and process-based ACRU model is appropriate for use in land use change and climatic change impact studies as shown through a space for time study; • that the contributions of different land uses to the streamflow generated from a catchment is not proportional to the relative area of that land use and that, as the mean annual precipitation of a subcatchment decreases, so the disparities between the relative areas a land use occupies and its contribution to catchment streamflow increases; • that specific land use changes have a greater impact on different components of the hydrological response of a catchment; • that land uses which currently have significant impacts on catchment water resources will place proportionally greater impacts on the catchment’s water resources if the climate were to become drier; thus the drier the climate becomes, the more relatively significant the role of land use becomes; • that when considering any hydrological impacts of land use change, climate change or combined land use and climate change, assessments need to consider the scale where the localized impacts may be evident, the progression of the impacts as the streamflow cascades through the catchment, as well as the impacts at the whole catchment scale where the accumulation of the effects through the catchment are evident; and lastly • that each catchment is unique with its own complexities, feed forwards and feedbacks, thus each catchment will have a unique threshold as to where land use change or climate change begins to have a significant influence of the hydrological response. Given these complex interactions between land use, climate and water, there is a growing imperative to improve the understanding of the movement of water within catchments, to be receptive and adaptive to new concepts and information, and to developing resilient and adaptive water management strategies for the future in a way that minimises the risks and maximises the benefits to potential impacts of climate change.
Integrating hydro-climatic hazards and climate changes as a tool for adaptive water resources management in the Orange River Catchment.
(2012) Knoesen, Darryn Marc.; Schulze, Roland Edgar.; Smithers, Jeffrey Colin.
The world’s freshwater resources are being placed under increasing pressure owing to growth in population, economic development, improved standards of living, agricultural intensification (linked mainly to irrigation), pollution and mismanagement of available freshwater resources. Already, in many parts of the Orange River Catchment, water availability has reached a critical stage. It has become increasingly evident that water related problems can no longer be resolved by water managers alone, owing to the problems becoming more interconnected with other development related issues, as well as with social, economic, environmental, legal and political factors. With the advent of climate change and the likelihood of increases in extreme events, water managers’ awareness of uncertainties and critical reflections on the adequacy of current management approaches is increasing. In order to manage water resources effectively a more holistic approach is required than has hitherto been the case, in which technological, social and economic development are linked with the protection of natural ecosystems and with dependable projections of future climatic conditions. To assess the climate risk connected with rural and urban water management, and to develop adaptive strategies that can respond to an increasingly variable climate that is projected into the future and help to reduce adverse impacts, it is necessary to make connections between climate related hazards, climate forecasts as well as climate change, and the planning, design, operation, maintenance, and rehabilitation of water related infrastructure. Therefore, adaptive water resources management (AWRM), which in essence is “learning by doing”, is believed to be a timely extension of the integrated water resources management (IWRM) approach as it acknowledges uncertainty and is flexible in that it allows for the adjustment of actions based on information learned about the system. Furthermore, it is suggested that climate risk management be imbedded within the AWRM framework. The objective of the research presented in this thesis is to develop techniques to integrate state-of-the-art climate projection scenarios – which forms part of the first step of the adaptive management cycle – downscaled to the regional/local scale, with hydro-climatic hazard determination – which forms part of the first step in the risk management process – in order to simulate projected impacts of climate change on hydro-climatic hazards in the Orange River Catchment (defined in this study as those areas of the catchment that exist within South Africa and Lesotho). The techniques developed and the results presented in this study can be used by decision-makers in the water sector in order to make informed proactive decisions as a response to projected future impacts of hydro-climatic hazards – all within a framework of AWRM. Steps towards fulfilling the above-mentioned objective begins by way of a comprehensive literature review; firstly of the study area, where it is identified that the Orange River Catchment is, in hydro-climatic terms, already a high risk environment; and secondly, of the relevant concepts involved which are, for this specific study, those pertaining to climate change, and the associated potential hydro-climatic impacts. These include risk management and its components, in order identify how hazard identification fits into the broader concept of risk management; and water resources management practices, in order to place the issues identified above within the context of AWRM. This study uses future projections of climate from five General Circulation Models, all using the SRES A2 emission scenario. By and large, however, where techniques developed in this study are demonstrated, this is done using the projections from the ECHAM5/MPI-OM GCM which, relative to the other four available GCMs, is considered to provide “middle of the road” projections of future climates over southern Africa. These climate projections are used in conjunction with the locally developed and widely verified ACRU hydrological model, as well as a newly developed hydro-climatic database at a finer spatial resolution than was available before, to make projections regarding the likelihood and severity of hydro-climatic hazards that may occur in the Orange River Catchment. The impacts of climate change on hydro-climatic hazards, viz. design rainfalls, design floods, droughts and sediment yields are investigated, with the results including a quantitative uncertainty analysis, by way of an index of concurrence from multiple GCM projections, for each of the respective analyses. A new methodology for the calculation of short duration (< 24 hour) design rainfalls from daily GCM rainfall projections is developed in this study. The methodology utilises an index storm approach and is based on L-moments, allowing for short duration design rainfalls to be estimated at any location in South Africa for which daily GCM rainfall projections exist. The results from the five GCMs used in this study indicate the following possible impacts of climate change on hydro-climatic hazards in the Orange River Catchment: · Design rainfalls of both short and long duration are, by and large, projected to increase by the intermediate future period represented by 2046 - 2065, and even more so by the more distant future period 2081 - 2100. · Design floods are, by and large, projected to increase into the intermediate future, and even more into the more distant future; with these increases being larger than those projected for design rainfalls. · Both meteorological and hydrological droughts are projected to decrease, both in terms of magnitude and frequency, by the period 2046 - 2065, with further decreases projected for the period 2081 - 2100. Where increases in meteorological and hydrological droughts are projected to occur, these are most likely to be in the western, drier regions of the catchment. · Annual sediment yields, as well as their year-to-year variability, are projected to increase by the period 2046 - 2065, and even more so by the period 2081 - 2100. These increases are most likely to occur in the higher rainfall, and especially in the steeper, regions in the east of the catchment. Additionally, with respect to the above-mentioned hydro-climatic hazards, it was found that: · The statistic chosen to describe inter-annual variability of hydro-climatic variables may create different perceptions of the projected future hydroclimatic environment and, hence, whether or not the water manager would decide whether adaptive action is necessary to manage future variability. · There is greater uncertainty amongst the GCMs used in this study when estimating design events (rainfall and streamflow) for shorter durations and longer return periods, indicating that GCMs may still be failing to simulate individual extreme events. · The spatial distribution of projected changes in meteorological and hydrological droughts are different, owing to the complexities introduced by the hydrological system · Many areas may be exposed to increases in hydrological hazards (i.e. hydrological drought, floods and/or sediment yields) because, where one extreme is projected to decrease, one of the others is often projected to increase. The thesis is concluded with recommendations for future research in the climate change and hydrological fields, based on the experiences gained in undertaking this study.
An assessment of canopy and litter interception in commercial and indigenous forests in the KwaZulu-Natal Midlands, South Africa.
(2011) Bulcock, Hartley Hugh.; Jewitt, Graham Paul Wyndham.
Understanding of the hydrological cycle and processes such as interception span as far back as the times of the Renaissance, when Leonardo da Vinci (1452-1519) first described it. However, there remains a gap in the knowledge of both canopy and litter interception in South African forest hydrology. Interception is typically considered to constitute only a small portion of total evaporation and in some models is disregarded or merely lumped with total evaporation, and not considered as a separate process. Interception is a threshold process, as a certain amount of water is required before successive processes such as infiltration and runoff can take place. Therefore an error introduced in modelling interception, especially disregarding it, will automatically introduce errors in the calibration of subsequent models/processes. In this study, field experiments to assess these two poorly understood hydrological processes, viz. canopy and litter interception were established for the three main commercial forestry genera in South Africa, namely, Pinus, Acacia and Eucalyptus as well as an indigenous Podocarpus henkelii stand, thus, accounting for interception of “broad leaf”, “compound leaf” and “needle leaf” trees in order to provide further insight into these processes. The study took place at two locations in the KwaZulu-Natal Midlands over a period of three years. The first site is the Two Streams catchment, located in the Seven Oaks area, about 70km north-east of Pietermaritzburg where the study on the commercial plantation species took place. The second site was the Podocarpus henkelii stand in Karkloof near Howick, 40km north of Pietermaritzburg. From the field data collected (cf. Chapter 2) it was observed that canopy storage capacity, an important parameter governing interception, was not constant and changed with rainfall intensity, with lower intensity events resulting in a higher storage capacity. Building on these findings, a physically based canopy interception model that is based on the well known Gash model was developed, and is referred to herein as the “variable storage Gash model”. While canopy interception is dependent on many factors including the storage capacity, potential evaporation, rainfall intensity and rainfall duration, the litter interception is largely dependent on the storage capacity due to the evaporative drivers under the canopy such as radiation, temperature and wind speed being moderated by the above canopy. From these finding, a litter interception model based on idealised drying curves from litter samples collected at the study sites was also developed (cf. Chapter 3). From the field data, it was found that the canopy interception for Eucalyptus grandis, Acacia mearnsii and Pinus patula was 14.9, 27.7 and 21.4% of mean annual precipitation (MAP) respectively. The simulated canopy interception using the “variable storage Gash model” was 16.9%, 26.6% and 23.3% for E. grandis, A. mearnsii and P. patula respectively. The litter interception measured for E. grandis, A. mearnsii and P. patula was found to be 8.5, 6.6 and 12.1% of MAP respectively, while the simulated litter interception using the idealised drying curve model corresponded well with the measured results and were 10.1%, 5.4% and 13.4% for E. grandis, A. mearnsii and P. patula respectively. The idealised drying curve model is site and species specific and is therefore not transferable to other locations. Conversely, the “variable storage Gash model” is transferable as it is not site and species specific, and relies on readily measureable and available information. Building on field studies, this was then used to simulate the canopy interception for Eucalyptus, Acacia mearnsii and Pinus in South Africa (including Lesotho and Swaziland) for all quinary catchments in which commercial forestry could be grown, i.e. a mean annual precipitation of greater than 600 mm.year-1 (cf. Chapter 4). It was found that, depending on the location and genus, canopy interception loss can be as high as 100 to 300 mm per year or approximately 10% to 40% of MAP. This relates to a mean interception loss of between 1.0 and 3.0 mm per rainday, highlighting the spatial variability of canopy interception. To further investigate the spatial variability of canopy interception, at various spatial scales, remote sensing technology was applied to estimate leaf area index (LAI) for use in modelling/estimating canopy storage capacity and canopy interception (cf. Chapter 6). The NDVI, SAVI and Vogelmann 1 vegetation indices were used in the estimation of the LAI. It was found the Vogelmann 1 index produced the best results. As models to estimate canopy interception typically require LAI and storage capacity, it was calculated that the ability to estimate these parameters over large areas is valuable for water resources managers and planners. An often neglected consideration of canopy and litter interception is its role in determining the water use efficiency (WUE) of a forest stand (cf. Chapter 5). This component of the study was undertaken in an indigenous Podocarpus henkelii stand as well as a commercial Pinus patula stand in Karkloof in the KwaZulu-Natal Midlands. The sap flow (transpiration) was measured in both the P. henkelii and P. patula stands using the using the Heat Pulse Velocity (HPV) technique in order to determine the productive green water use. The canopy and litter interception was measured in the P. henkelii site, but was modelled in the P. patula site using the “variable storage Gash” and idealised drying curve models, in order to estimate the non-productive green water use. It was found that the canopy and litter interception for P. henkelii was 29.8% and 6.2% respectively, while the modelled canopy and litter interception for P. patula was 22.1% and 10.7% respectively. If only the productive green water use (transpiration) is considered, then the water use efficiency of P. henkelii and P. patula was found to be 7.14 g.mm-1 and 25.21 g.mm-1 respectively. However, from a water management perspective it is important to consider the total green water use efficiency (transpiration + interception), which reveals a significantly lower water use efficiency of 3.8 g.mm-1 and 18.8 g.mm-1 for P. henkelii and P. patula respectively. To extend the study to a globally relavent issue, the possible impact of climate change on canopy interception was investigated, as forests growth is critically linked to climate (cf. Chapter 7). To achieve this, the CABALA model was used to model LAI and transpiration of Eucalyptus grandis and Pinus patula under 9 different climate change scenarios, including changes in temperature, rainfall and atmospheric CO2. The simulated LAI values from the CABALA model for all 9 climate scenarios were then used to simulate canopy interception using the “variable storage Gash model”. Results show that LAI may increase by as much as 24% and transpiration may decrease by as much as 13%, depending on the scenario, location and tree species. However, it was found that canopy interception does not change greatly, leading to the conclusion that under climate change conditions, canopy interception may not become a more dominant component of the hydrological cycle than it currently is as the changes under climate change are likely to be less than the natural variability from year to year. However, canopy interception remains an important consideration for water resources management and planning both currently and in the future.
Development and evaluation of model-based operational yield forecasts in the South African sugar industry.
(2005) Bezuidenhout, Carel Nicolaas.; Schulze, Roland Edgar.
South Africa is the largest producer of sugar in Africa and one of the ten largest sugarcane producers in the world. Sugarcane in South Africa is grown under a wide range of agro-climatic conditions. Climate has been identified as the single most important factor influencing sugarcane production in South Africa. Traditionally, sugarcane mill committees have issued forecasts of anticipated production for a region. However, owing to several limitations of such committee forecasts, more advanced technologies have had to be considered. The aim of this study has been to develop, evaluate and implement a pertinent and technologically advanced operational sugarcane yield forecasting system for South Africa. Specific objectives have included literature and technology reviews, surveys of stakeholder requirements, the development and evaluation of a forecasting system and the assessment of information transfer and user adoption. A crop yield model-based system has been developed to simulate representative crops for derived Homogeneous Climate Zones (HCZ). The system has integrated climate data and crop management, soil, irrigation and seasonal rainfall outlook information. Simulations of yields were aggregated from HCZs to mill supply area and industry scales and were compared with actual production. The value of climate information (including climate station networks) and seasonal rainfall outlook information were quantified independently. It was concluded that the system was capable of forecasting yields with acceptable accuracy over a wide range of agro-climatic conditions in South Africa. At an industry scale, the system captured up to 58% of the climatically driven variability in mean annual sugarcane yields. Forecast accuracies differed widely between different mill supply areas, and several factors were identified that may explain some inconsistencies. Seasonal rainfall outlook information generally enhanced forecasts of sugarcane production. Rainfall outlooks issued during the summer months seemed more valuable than those issued in early spring. Operationally, model-based forecasts can be expected to be valuable prior to the commencement of the milling season in April. Current limitations of forecasts include system calibration, the expression of production relative to that of the previous season and the omission of incorporating near real-time production and climate information. Several refinements to the forecast system are proposed and a strong collaborative approach between modellers, climatologists, mill committees and other decision makers is encouraged.
Refinement of modelling tools to assess potential agrohydrological impacts of climate change in southern Africa.
(2001) Perks, Lucille Annalise.; Schulze, Roland Edgar.
Changes in climate due to anthropogenic influences are expected to affect both hydrological and agricultural systems in southern Africa. Studies on the potential impacts of climate change on agrohydrological systems had been performed previously in the School of Bioresources Engineering and Environmental Hydrology (School of BEEH). However, refinement of these modelling tools and restructuring of the databases used was needed to enable more realistic and dynamic simulations of the impacts of changes in climate. Furthermore, it was realised that modifications and linkages of various routines would result in a faster processing time to perform climate impact assessments at the catchment scale. Baseline ("present") climatic information for this study was obtained from the School of BEEH's database. Scenarios of future climate were obtained from six General Circulation Models (GCMs). Output from the five GCMs which provided monthly climate output was used in the climate impact assessments carried out. Potential changes in variability of rainfall resulting from climate change was assessed using the daily climate output from the sixth GCM. As the spatial resolution of the climatic output from these GCMs was too coarse for use in climate impact studies the GCM output was interpolated to a finer spatial resolution. To assess the potential impact of climate change on water resources in southern Africa the ACRU hydrological modelling system was selected. The ACRU model was, however, initially modified and updated to enable more dynamic simulation of climate change. In previous hydrological studies of climate change in southern Africa Quaternary Catchments were modelled as individual, isolated catchments. To determine the potential impact of changes in climate on accumulated flows in large catchments the configuration of the Quaternary Catchments needed to be determined and this configuration used in ACRU. The changes in hydrological responses were calculated both as absolute differences between future and present values and the ratio offuture hydrological response to the present response. The large degree of uncertainty between the GCMs was reflected in the wide range of results obtained for the water resources component of this study. In addition to the climate impact studies, sensitivity and threshold studies were performed using ACRU to assess the vulnerability of regions to changes in climate. Potential change in the yields and distributions of parameters important to agriculture, such as heat units, crops, pastures and commercial tree species were assessed using simple crop models at a quarter ofdegree latitude / longitude scale. Most species were simulated to show decreases in yields and climatically suitable areas. There are many sources of uncertainties when performing climate impact assessments and the origins of these uncertainties were investigated. Lastly, potential adaptation strategies for southern Africa considering the results obtained are presented.
Assessment of agro-ecosystem sustainability across varying scales in South Africa.
(2005) Walker, Nicholas James.; Schulze, Roland Edgar.
Maize production plays an important socio-economic role in rural communities of the Highveld region of South Africa, yet it is becoming increasingly difficult to produce maize economically with current agricultural policy conditions and existing management systems. This has direct socio-economic impacts for both commercial farmer and small-scale farmer. Sustainable commercial maize production is not only a question of yields, but also of protection of the environmental resource base, social welfare, and the livelihoods of farmers per se as well as the surrounding rural and urban communities. Sustainability for the small-scale farmer, on the other hand raises questions of equity, economic viability and household food security. Therefore, information is required to ascertain whether an existing agro-ecosystem can be identified as sustainable, and what facets of that system make it sustainable or unsustainable. To begin to answer these key questions it is important to state, and to some extent attempt to standardise, the definitions of agricultural sustainability. Agro-ecosystem sustainability with regard to maize production was assessed at the regional scale of the Highveld of South Africa as well as at, the Quaternary Catchment scale and the smallholder farm scale. Von Wiren-Lehr's (2001) goal orientated system was considered an appropriate and practical system by which agro-ecosystem sustainability across a range of scales could be investigated. At the regional scale, optimum management strategies for each of the 497 Quaternary Catchments in the Highveld region were devised, based on present climatic conditions and using an index which was based on mean yields and yield variability. Economic returns and their impact on sustainability were then also assessed under plausible future climate scenarios. At the Quaternary Catchment scales optimum management strategies were ascertained by using a sustainability index. These strategies were then modelled under present and plausible future climate scenarios. The results from the sustainability modelling showed that a maize crop will benefit, especially with respect to mean grain yields, from an effective doubling of atmospheric CO2 concentrations. However, this benefit can be counteracted when there is a concurrent increase in temperature, particularly of 2°C or more. At the smallholder scale, a range of management options was assessed. These options included several types of tillage practices in combination with applications of either inorganic fertiliser or manure. The management strategies were modelled under present climate conditions and under plausible climate change scenarios for southern Africa. The conventional tillage type (disc) was ranked highest under most of the climatic conditions modelled, including present climate conditions. This was in contrast to actual yields from smallholder farmers (-1 ha field size) in the Potshini area, near Bergville in the KwaZuluNatal province of South Africa, who have experienced an increase in yield when conservation tillage practices have been used on their land (Smith et al., 2004). The sustainability of agro-ecosystems depends on the maintenance of the economic, biophysical and social components that make up the system (Belcher et al., 2004). The modelling performed for the Highveld region built on previous work and for the first time incorporated daily temperatures and ISCW soil information into CERES-Maize. The intention was to incorporate other agro-ecosystem functions, as well as yield, into the sustainability assessment. Only limited research has previously been carried out in South Africa with respect to modelling smallholder agro-ecosystems and sustainability. This research sought to model the smallholder system along with the impacts that climate change would have on sustainability and associated food security.

Browse

Recent Submissions