A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree Of Master Of Science in Engineering. / The temporal distribution of rainfall can have a significant effect on peak runoff, especially so in the small catchments that are typical of the Witwatersrand. This report investigates the shape of the natural hyetoraph and its use in the analysis of peak runoff. It describes the climatology of the sub-continent and rain-producing systems. Then more specifically, aspects of rainfall over Johannesburg are discussed. Some Of the more commonly-used temporal distributions of rainfall are reviewed and the relationship between intensity-time distributions and mass curves is illustrated. Mass curves are derived using data from a rain gauge in Norwood, Johannesburg. The data is analysed with the assistance of a computer program and classified into quartiles. The quartiles are further analysed in an attempt to define their characteristics in greater detail. The mass curves are used wIth a hydrological model to generate hydrographs. The values of runoff peaks are found to be comparable with those obtained using currently accepted temporal rainfall distributions. / AC 2018

Water vapour content and transport over southern Africa and adjacent oceans are examined. Early summer rainfall over the northern and central interior of South Africa tends to be associated with baroclinic controls whereas late-summer rainfall is barotropic in origin. This is reflected in the northwesterly water vapour transport from an Atlantic Ocean source by middle and upper tropospheric westerly waves in early summer. A thermally indirect Ferrel cell, indicated-from energetics, COpIU1nSthe· temperate nature of the early-summer atmosphere over southern Africa. Late summer water vapour transport, in contrast, is strongly from the tropics, with' a reduced eddy component, indicating an important tropical control on late SUmmerrainfall especially in terms of fluctuations in the position of the ascending limb of .the Walker cell Over southern Africa. The Hadley cell is of importance to the late summer rainfall in that dry (wet) years are associated with an anomalous cell OVereastern (central) South Africa such that low level vapour transport is southerly (northerly). The anticyclone over the eastern parts of southern Africa, coupled with. a trough over the interior (especially at the 700 hPa pressure level), is important for the introduction of water vapour over the subcontinent in wet and dry years and for tropical-temperate trough case studies. Water vapour source regions differ from early summer (Atlantic Ocean) to late summer (Indian Ocean), which reflects the temperate. control on early and the tropical control on late summer circulation. The convergence of water vapour over southern Africa in wet years and during tropical-temperate troughs is not only important for cloud formation and precipitation, but also for latent heat release associated with convergent water vapour. Diabatic heating decreases the stability of the tropical atmosphere thereby resulting in increased vertical motion. It also forces an anomalous Badley circulation during wet late summers and tropical-temperate trough .cases as a result of complex energy transformations. Heating increases eddy available potential energy which is converted to zonal available potential energy by a thermally indirect circulation found in the tropics. The zonal potential energy is then converted to kinetic energy by the thermally direct Badley cell. Water vapour and its variations are thus important for the precipitation, heating and SUbsequent energy of the subtropical southern African atmosphere, / GR 2017

The concept of Intensity Duration Frequency (IDF) relationship curve presents crucial design contribution for several decades under the assumption of a stationary climate, the frequency and intensity of extreme rainfall nonetheless seemingly increase worldwide. Based on the research conducted in recent years, the greatest increases are likely to occur in short-duration storms lasting less than a day, potentially leading to an increase in the magnitude and frequency of flash floods. The trend analysis of the precipitation influencing the climate variability and extreme rainfall in the state of Florida is conducted in this study. Since these local changes are potentially or directly related to the surrounding oceanic-atmospheric oscillations, the following oscillations are analyzed or highlighted in this study: Atlantic Multi-Decadal Oscillation (AMO), El Niño Southern Oscillation (ENSO), and Pacific Decadal Oscillations (PDO). Collected throughout the state of Florida, the precipitation data from rainfall gages are grouped and analyzed based on type of duration such as short-term duration or minute, in hourly and in daily period. To assess statistical associations based on the ranks of the data, the non-parametric tests Kendall’s tau and Spearman’s rho correlation coefficient are used to determine the orientation of the trend and ultimately utilize the testing results to determine the statistical significance of the analyzed data. The outcome of the latter confirms with confidence whether there is an increasing or decreasing trend in precipitation depth in the State of Florida. The main emphasis is on the influence of rainfall extremes of short-term duration over a period of about 50 years. Results from both Spearman and Mann-Kendall tests show that the greatest percentage of increase occurs during the short rainfall duration period. The result highlights a tendency of increasing trends in three different regions, two of which are more into the central and peninsula region of Florida and one in the continental region. Given its topography and the nature of its water surface such as the everglades and the Lake Okeechobee, Florida experience a wide range of weather patterns resulting in frequent flooding during wet season and drought in the dry season. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / This project investigates the influence that rainfall and temperature patterns have on mammal drinking patterns at an artificial waterhole in KGNP at Nossob. On a regional scale, this project investigates long-term rainfall and temperature trends over three/four decades, and in some instances the past 100 years, respectively for KGNP using climate records from weather stations located within the park and adjacent areas. This project makes use of KGNP census data to observe spatio-temporal distributions of large mammals in relation to rainfall (and to a lesser extent temperature) variability. Investigations assess whether relationships exist between faunal movement and distribution and rainfall volume and frequency. On a local scale, this project makes use of webcam images measured at 15-second intervals to establish mammalian drinking patterns and waterhole use over a short time scale (October 2012 – December 2014). The climate data for Twee Rivieren, Mata-Mata, Nossob and Upington reveal statistically significant increases in Tmax (av. 0.04°C) over the study period, whilst in summary, mean regional temperatures have increased by almost 1.6°C over the past 40 years. Rainfall patterns have revealed a north to south gradient in KGNP, where the northern and central parts of the park are becoming drier and the southern parts are becoming wetter. This demonstrates rainfall variability throughout KGNP over the period 2004 - 2013. This study established a positive relationship between faunal distributions and rainfall patterns within the park, showing that certain species are highly reliant on rainfall as a source of drinking water. It has been established that herbivore species are more reliant on the water trough during the dry season, when surface water is not available. However, there is an even spread of carnivore species water trough usage during the wet and dry season throughout the year. It has been established that during rainfall events exceeding ca. 30mm, faunal species prefer to utilise the natural surface water rather than the artificial waterhole at Nossob. Water trough usage under different temperature thresholds has revealed that groups of species (carnivores and herbivores) drinking patterns shift to either earlier or later in the day when temperatures increase, in order to avoid heat stress. Changing rainfall patterns could drastically cause water shortages, which will negatively affect the amount of available drinking water for mammals within KGNP. This study is important in contributing to an improved management of KGNP through providing a quantitative description of the relationship of mammal visitation at water troughs to the ambient climate. This is particularly valuable as climate change projections for the region suggest progressive drying. Water troughs will become an important source of moisture. / LG2017

"May 2002" Includes list of papers published during this study Errata slip inserted inside back cover of v. 1 Includes bibliographical references (leaves 331-357) V. 1. [Text} -- v. 2. Appendices Develops an alternative design flood estimation methodology. Establishing a relationship between catchment characteristics and the rainfall excess frequency duration proportions enables the definition of these proportions for generic catchment types, increasing the potential for translation to catchments with limited data but similar hydrographic properties, thereby improving design process.

This study aimed to determine whether rainfall regime has driven differentiation in the Australian perennial grass, Austrodanthonia caespitosa, resulting in local ecotypes possessing characters, such as deep rootedness or summer activity, that may be particularly useful in reducing deep drainage for salinity mitigation, or whether the species shows a plastic response in root growth to soil water distribution. Rainfall regime varies within a given annual rainfall because size and ditribution of rainfall event vary. This can have an important effect on soil water distribution, both spatially and temporally. This study investigates the relationship between rainfall regime and the structure of root systems in local populations of Austrodanthonia caespitosa (Gaudich.), Firstly, it examined a number of indices useful in quantifying variation in small-scale rainfall regime, including seasonal bias, event size, event frequency, and the clustering of events, as well as how rainfall event size may be changing over time across Australia. The variation in soil water distribution that results from different rainfall regimes is expected to interact with root distribution in plants, either acting as a selective force and driving genotypic differentiation in response to soil water availability, or through plasticity in root placement. The relationship between rainfall regime and root depth distribution was examined in Austrodanthonia caespitosa (Gaudich.), or white-top wallaby grass, a perennial grass common across southern Australia. Growth and reproductive traits of plants grown from seeds collected from across the range of this species under a single rainfall regime were compared and correlated with the rainfall indices and soil type in order to establish possible abiotic explanations for trait variability. Phenological characters were found to be particularly variable between ecotypes, but high local variation between ecotypes suggested factors operating on a spatial scale smaller than the rainfall gradients are responsible for population differentiation. In order to investigate the interaction between rainfall event size and root depth, an experiment was conducted to investigate plant response to watering pulse size and frequency, with plants grown under a range of controlled watering regimes, and root depth distribution compared. The primary response in root growth was plastic, with shallow roots being developed under small, frequent events, and deep roots developed under large, infrequent waterings. Differences between ecotypes were less important, and there was no interaction between ecotype and watering treatment, indicating the same degree of plasticity in all ecotypes. Plants from a range of populations were grown under a controlled climate, first under winter conditions, then under summer conditions, with summer water withheld from half the plants, in order to determine the response to summer watering and summer drought. Plants that were watered over summer showed a strong growth response, increasing shoot biomass significantly. This effect was particularly strong in South Australian populations, which was unexpected as they originate from a region with low, unpredictable summer rainfall. Root depth was not strongly influenced by summer watering treatment. Finally, an evolutionary algorithm model was constructed in order to examine optimal plant traits under a variety of rainfall regimes. The model highlighted the importance of the interaction between rainfall regime and soil type in determining optimal root placement. Variable root cost with depth was also found to be an important trade-off to be considered, with high root loss in the surface soil layers, due to high temperatures, making a shallow rooted strategy less efficient than if root costs were equal throughout the root system. Overall, no ecotypes of A.caespitosa could be identified that had characters particularly suited to deep drainage reduction, as the drought tolerant nature of the species, and the dormancy during times of drought, may lead to low overall water use. However, it may be a useful native component in pasture systems, due to its strong growth response to summer rainfall, a characteristic found to be particularly strong in a number of South Australian ecotypes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

"May 2002" / Includes list of papers published during this study / Errata slip inserted inside back cover of v. 1 / Includes bibliographical references (leaves 331-357) / 2 v. : ill. (some col.), col. maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Develops an alternative design flood estimation methodology. Establishing a relationship between catchment characteristics and the rainfall excess frequency duration proportions enables the definition of these proportions for generic catchment types, increasing the potential for translation to catchments with limited data but similar hydrographic properties, thereby improving design process. / Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 2002

No description available.

Policy makers, water managers, farmers and many other sectors of the society in southern Africa are confronting increasingly complex decisions as a result of the marked day-to-day, intra-seasonal and inter-annual variability of climate. Hence, forecasts of hydro-climatic variables with lead times of days to seasons ahead are becoming increasingly important to them in making more informed risk-based management decisions. With improved representations of atmospheric processes and advances in computer technology, a major improvement has been made by institutions such as the South African Weather Service, the University of Pretoria and the University of Cape Town in forecasting southern Africa’s weather at short lead times and its various climatic statistics for longer time ranges. In spite of these improvements, the operational utility of weather and climate forecasts, especially in agricultural and water management decision making, is still limited. This is so mainly because of a lack of reliability in their accuracy and the fact that they are not suited directly to the requirements of agrohydrological models with respect to their spatial and temporal scales and formats. As a result, the need has arisen to develop a GIS based framework in which the “translation” of weather and climate forecasts into more tangible agrohydrological forecasts such as streamflows, reservoir levels or crop yields is facilitated for enhanced economic, environmental and societal decision making over southern Africa in general, and in selected catchments in particular. This study focuses on the development of such a framework. As a precursor to describing and evaluating this framework, however, one important objective was to review the potential impacts of climate variability on water resources and agriculture, as well as assessing current approaches to managing climate variability and minimising risks from a hydrological perspective. With the aim of understanding the broad range of forecasting systems, the review was extended to the current state of hydro-climatic forecasting techniques and their potential applications in order to reduce vulnerability in the management of water resources and agricultural systems. This was followed by a brief review of some challenges and approaches to maximising benefits from these hydro-climatic forecasts. A GIS based framework has been developed to serve as an aid to process all the computations required to translate near real time rainfall fields estimated by remotely sensed tools, as well as daily rainfall forecasts with a range of lead times provided by Numerical Weather Prediction (NWP) models into daily quantitative values which are suitable for application with hydrological or crop models. Another major component of the framework was the development of two methodologies, viz. the Historical Sequence Method and the Ensemble Re-ordering Based Method for the translation of a triplet of categorical monthly and seasonal rainfall forecasts (i.e. Above, Near and Below Normal) into daily quantitative values, as such a triplet of probabilities cannot be applied in its original published form into hydrological/crop models which operate on a daily time step. The outputs of various near real time observations, of weather and climate models, as well as of downscaling methodologies were evaluated against observations in the Mgeni catchment in KwaZulu-Natal, South Africa, both in terms of rainfall characteristics as well as of streamflows simulated with the daily time step ACRU model. A comparative study of rainfall derived from daily reporting raingauges, ground based radars, satellites and merged fields indicated that the raingauge and merged rainfall fields displayed relatively realistic results and they may be used to simulate the “now state” of a catchment at the beginning of a forecast period. The performance of three NWP models, viz. the C-CAM, UM and NCEP-MRF, were found to vary from one event to another. However, the C-CAM model showed a general tendency of under-estimation whereas the UM and NCEP-MRF models suffered from significant over-estimation of the summer rainfall over the Mgeni catchment. Ensembles of simulated streamflows with the ACRU model using ensembles of rainfalls derived from both the Historical Sequence Method and the Ensemble Re-ordering Based Method showed reasonably good results for most of the selected months and seasons for which they were tested, which indicates that the two methods of transforming categorical seasonal forecasts into ensembles of daily quantitative rainfall values are useful for various agrohydrological applications in South Africa and possibly elsewhere. The use of the Ensemble Re-ordering Based Method was also found to be quite effective in generating the transitional probabilities of rain days and dry days as well as the persistence of dry and wet spells within forecast cycles, all of which are important in the evaluation and forecasting of streamflows and crop yields, as well as droughts and floods. Finally, future areas of research which could facilitate the practical implementation of the framework were identified. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Natural phenomena such as rainfall are responsible for communication service disruption, leading to severe outages and bandwidth inefficiency in both terrestrial and satellite systems, especially above 10 GHz. Rainfall attenuation is a source of concern to radio engineers in link budgeting and is primarily related to the rainfall mechanism of absorption and scattering of millimetric signal energy. Therefore, the study of rainfall microstructure can serve as a veritable means of optimizing network parameters for the design and deployment of millimetric and microwave links. Rainfall rate and rainfall drop-size are two microstructural parameters essential for the appropriate estimation of local rainfall attenuation. There are several existing analytical and empirical models for the prediction of rainfall attenuation and their performances largely depend on regional and climatic characteristics of interest. In this study, the thrust is to establish the most appropriate models in South African areas for rainfall rate and rainfall drop-size. Statistical analysis is derived from disdrometer measurements sampled at one-minute interval over a period of two years in Durban, a subtropical site in South Africa. The measurements are further categorized according to temporal rainfall regimes: drizzle, widespread, shower and thunderstorm. The analysis is modified to develop statistical and empirical models for rainfall rate using gamma, lognormal, Moupfouma and other ITU-R compliant models for the control site. Additionally, rain drop-size distribution (DSD) parameters are developed from the modified gamma, lognormal, negative exponential and Weibull models. The spherical droplet assumption is used to estimate the scattering parameters for frequencies between 2 GHz and 1000 GHz using the disdrometer diameter ranges. The resulting proposed DSD models are used, alongside the scattering parameters, for the prediction and estimation of rainfall attenuation. Finally, the study employs correlation and regression techniques to extend the results to other locations in South Africa. The cumulative density function analysis of rainfall parameters is applied for the selected locations to obtain their equivalent models for rainfall rate and rainfall DSD required for the estimation of rainfall attenuation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.