Climate change and a growing demand for freshwater resources due to population increases and socio-economic changes will make water a limiting factor (in terms of both quantity and quality) in development. The need for reliable quantitative estimates of water availability cannot be over-emphasised. However, there is frequently a paucity of the data required for this quantification as many basins, especially in the developing world, are inadequately equipped with monitoring networks. Existing networks are also shrinking due mainly to shortages in human and financial resources. Over the past few decades mathematical models have been used to bridge the data gap by generating datasets for use in management and policy making. In southern Africa, the Pitman monthly rainfall-runoff model has enjoyed relatively popular use as a water resources estimation tool. However, it is acknowledged that models are abstractions of reality and the data used to drive them is imperfect, making the model outputs uncertain. While there is acknowledgement of the limitations of modelled data in the southern African region among water practitioners, there has been little effort to explicitly quantify and account for this uncertainty in water resources estimation tools and explore how it affects the decision making process. Uncertainty manifests itself in three major areas of the modelling chain; the input data used to force the model, the parameter estimation process and the model structural errors. A previous study concluded that the parameter estimation process for the Pitman model contributed more to the global uncertainty of the model than other sources. While the literature abounds with uncertainty estimation techniques, many of these are dependent on observations and are therefore unlikely to be easily applicable to the southern African region where there is an acute shortage of such data. This study focuses on two aspects of making hydrologic predictions in ungauged basins. Firstly, the study advocates the development of an a priori parameter estimation process for the Pitman model and secondly, uses indices of hydrological functional behaviour to condition and reduce predictive uncertainty in both gauged and ungauged basins. In this approach all the basins are treated as ungauged, while the historical records in the gauged basins are used to develop regional indices of expected hydrological behaviour and assess the applicability of these methods. Incorporating uncertainty into the hydrologic estimation tools used in southern Africa entails rethinking the way the uncertain results can be used in further analysis and how they will be interpreted by stakeholders. An uncertainty framework is proposed. The framework is made up of a number of components related to the estimation of the prior distribution of the parameters, used to generate output ensembles which are then assessed and constrained using regionalised indices of basin behavioural responses. This is premised on such indices being based on the best available knowledge covering different regions. This framework is flexible enough to be used with any model structure to ensure consistent and comparable results. While the aim is to eventually apply the uncertainty framework in the southern African region, this study reports on the preliminary work on the development and testing of the framework components based on South African basins. This is necessitated by the variations in the availability and quality of the data across the region. Uncertainty in the parameter estimation process was incorporated by assuming uncertainty in the physical and hydro-meteorological data used to directly quantify the parameter. This uncertainty was represented by the range of variability of these basin characteristics and probability distribution functions were developed to account for this uncertainty and propagate it through the estimation process to generate posterior distributions for the parameters. The results show that the framework has a great deal of potential but can still be improved. In general, the estimated uncertain parameters managed to produce hydrologically realistic model outputs capturing the expected regimes across the different hydro-climatic and geo-physical gradients examined. The regional relationships for the three indices developed and tested in this study were in general agreement with existing knowledge and managed to successfully provide a multi-criteria conditioning of the model output ensembles. The feedback loop included in the framework enabled a systematic re-examination of the estimation procedures for both the parameters and the indices when inconsistencies in the results were identified. This improved results. However, there is need to carefully examine the issues and problems that may arise within other basins outside South Africa and develop guidelines for the use of the framework. / iText 1.4.6 (by lowagie.com)

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Thesis (MSc. Agriculture (Pasture Science)) -- University of Limpopo, 2016. / The relationships between tree age, growth rings, and stem circumference correlated with establishment patterns may be a valuable instrument to reveal the functioning of woody species in the Savanna Biome. A study on tree age and establishment patterns of Acacia tortilis in the semi-arid regions of the Limpopo Province was conducted to aid an understanding of the causes of encroachment in savanna vegetation. This study aimed to determine the periodicity of growth ring formation at two study areas, correlate the number of growth rings with different tree characteristics and document tree population establishment patterns of Acacia tortilis, using stem circumferences. This was done in order to predict long-term bush encroachment using the interaction between rainfall and soil on the age, growth and establishment patterns of Acacia tortilis. Data was collected at three sites representing two study areas, two sites at the University of Limpopo’s Syferkuil Agricultural Experimental Farm and one site at the Sondela Nature Reserve in the Limpopo Province. The study incorporated two different soil forms and two rainfall regimes. Trees were divided into five height classes; namely, <0.5 m, >0.5 – 1.5 m, >1.5 – 2.0 m, >2.0 – 3.0 m and >3m. Fifty trees (ten in each class) were felled at each site, and the following recordings were made: tree height, stem circumference and crown diameter. Furthermore, each felled stump was taken to the laboratory and examined for growth rings. The results indicated that growth pattern of Acacia tortilis stems were more influenced by soil form than the amount of rainfall. Tree height was not significantly affected by soil form. However, rainfall proved to have a significant effect on the final height of the plant. Both rainfall and soil form did not have a substantial effect on the number of growth rings. Crown diameter was affected by soil form but rainfall did not prove to have the same effect. Correlations between growth rings and stem circumferences, tree height and crown diameter, proved to have significant relationships. However, the relationship between stem circumference and the number of growth rings was the most significant. iv A prediction model was created using the relationship between stem size and growth rings. Using this model tree age can be determined in a non-destructive manner. However, the absence of a correlation between rainfall and establishment strongly suggests that rainfall cannot be used, on its own, to determine the establishment sequence and the pattern of bush encroachment. The study suggests that natural developments responsible for establishment patterns and population dynamics of woody species are complex, and their effects are visible after an extensive period. Therefore, to understand these influential processes comprehensively, several seasons of observations and monitoring would be recommended. Future research on this particular topic should include more than one encroaching species, because this will provide a broader perspective on the encroachment patterns of bush communities. However, the focus should be on studying the influence of growth limiting factors such as soil and climatic impacts, as well as area-specific environmental factors on the growth of encroaching species, such as Acacia tortilis. Key words: Bush encroachment, dendrochronology, growth rings, tree age, savanna, stem circumference Note: The candidate and the supervisors are aware of the fact that the Acacia genus has been revised. However, in this dissertation, the genus and species Acacia tortilis is still used. Relevant changes will be used in future publications. / University of Limpopo’s Department of Agriculture and National Research Foundation

MENVSC / Department of Geography and Geo-Information Sciences / Out of all rain-producing weather systems, cut-off lows (COLs) are linked with the occurrence of high impact rainfall and in some cases short-lived floods which can last for 24 hours over South Africa. This study examined the characteristics associated with the present occurrence of the severe COL systems over South Africa from 2011 to 2017. The accuracy of the 4.4 km Unified Model (UM) which is currently in use for simulating areas of deep moist convection in South Africa was evaluated. The UM simulated geopotential height at 500 hPa as well as the associated 24 hours precipitation which were compared against the daily fields of geopotential height and 6-hourly precipitation from the European Centre for Medium-Range Weather Forecasts (ECMWF). COL events were categorized and analyzed according to the associated surface circulation patterns at 850 hPa. The seasonal distribution and duration of the systems over northern (10°E-33°E //22°-32°S) and southern (10°E-33°E //32°-35°S) regions of the study area were also analyzed. Results show COL systems shifting with season towards the north eastern parts of the country, with an increased number of events during the austral winter season during the study period. Systems which lasted for long time were observed during the austral winter and spring seasons. The UM tends to simulate areas of heavy precipitation accurately with poor simulation during the initial stages of the systems. The UM provided a more realistic-looking closed geopotential height and rainfall fields for systems which are coupled with a cold front at the surface. Application of the knowledge about the evolution in the characteristics of COL events from this study can improve the operational forecasting of these weather systems over the country. / NRF

Assessing and managing risks posed by climate variability and change is challenging in the tropics, from both a scientific and a socio-economic perspective. While our understanding of the tropical land rainfall variability and its future projection is highly uncertain, most of the vulnerable countries with a limited adaptation capability are within the tropical band. This dissertation combines a process-based physical understanding with observational analysis to characterize the spatio-temporal changes in the tropical land rainfall during a transient El Niño evolution, with an emphasis on the risk management of the dry and wet extremes. The broad objectives are two-fold: 1) To make better sense of the higher uncertainty in the tropical rainfall response to warming and 2) to improve climate risk management strategies in the tropical developing countries. An ENSO teleconnection mechanism, referred to as the tropical tropospheric temperature or TTT mechanism provides a theoretical framework to study the remote tropical land rainfall behavior during a transient El Niño warming. The TTT mechanism postulates that the tropic-wide free tropospheric warming interacts locally with the deep convection to modulate remote tropical climate. During the growth phase, anomalous free tropospheric temperature causes direct and fast atmospheric adjustments leading to tropospheric stability to deep moist convection and a drier response. Subsequently, during mature phase, a recovery of the initial rainfall deficit follows due to indirect and slower adjustments in surface temperature and humidity fields. In chapter 2 and 3 of this dissertation, the changes in the observed tropical land rainfall characteristics and other climate fields conditional on the growth and mature phase of El Niño warming are investigated and the role of dynamical and thermodynamic mechanisms as hypothesized by the TTT mechanism are elucidated. In chapter 4, an El Niño forecast based early action investment strategy is developed to reduce the socio-economic impacts of rainfall extremes at sub-seasonal to inter-annual lead time scales. In the part I (chapter 2), the analysis is conducted at a regional scale over the tropical Africa. Using the TTT mechanism, a physical explanation is provided for the contrasting rainfall response over the Western Sahel and tropical Eastern Africa during an El Niño. The study finds that the Western Sahel’s main rainy season (July-September) is affected by the growth phase of El Niño through (i) a lack of neighboring North Atlantic sea surface warming, (ii) an absence of an atmospheric column water vapor anomaly over the North Atlantic and Western Sahel, and (iii) higher atmospheric vertical stability over the Western Sahel, resulting in the suppression of mean seasonal rainfall as well as number of wet days. In contrast, the short rainy season (October-December) of tropical Eastern Africa is impacted by the mature phase of El Niño through (i) neighboring Indian Ocean sea surface warming, (ii) positive column water vapor anomalies over the Indian Ocean and tropical Eastern Africa, and (iii) higher atmospheric vertical instability over tropical Eastern Africa, leading to an increase in mean seasonal rainfall as well as in the number of wet days. While the modulation of the frequency of wet days and seasonal mean accumulation is statistically significant, daily rainfall intensity (for days with rainfall >1 mm/day), whether mean, median, or extreme, does not show a significant response in either region. Hence, the variability in seasonal mean rainfall that can be attributed to the El Niño–Southern Oscillation phenomenon in both regions is likely due to changes in the frequency of rainfall. These observed changes agree with the predictions of the TTT mechanism. In the part II (chapter 3), a global scale analysis is performed to more generally characterize the spatio-temporal differences in remote tropical land rainfall response to El Niño warming. The principal conclusions are: 1) during the El Niño growth phase relative to the neutral phase, rainfall decreases. A significant decrease in mean accumulation can be attributed to a significant increase in proportion of dry days and decrease in median and extreme intensity. A significant descent anomaly confirms the vertical stabilization and dominance of dynamical processes. 2) During the mature phase relative to the growth phase, rainfall increases, signifying a recovery from the suppression of deep moist convection. A significant increase in mean accumulation is accompanied by a decrease in proportion of dry days and by an increase in median and extreme intensity characteristics. The significant rise in the moisture field corroborates the dominance of thermodynamic processes. These findings are expected from the TTT mechanism and generalizes the findings of part I to the global scale. In the part III (chapter 4), an El Niño forecast based index insurance policy is developed that can be used as an early action investment instrument. The forecast insurance (FI) design framework is illustrated with an application to El Niño associated flood hazard during the January-February-March-April (JFMA) season over Piura region of Peru. In order to determine the economic utility of the system, a simple cost-loss decision model, incorporating the insurance cost, is developed. The main conclusion is that the proposed El Niño forecast insurance policy with the pre-event Niño1.2 index based trigger has significant reliability and substantial utility for a wide range of policy parameters considered. Relative to a no early action strategy, the advantage of the system generally increases with i) shortening in the lead time from 9 to 1 month, ii) increase in El Niño severity level from 10 to 50 year return period and iii) increase in avoidable loss to cost ratio (LCR) ratio from 1 to 1000. These results and the forecast insurance modeling and utility evaluation frameworks have implications for designing optimal contingent financial instruments for disaster risk reduction and climate change adaptation.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 53-54. / by James Che-Ming Chung. / M.S.

Indiana University-Purdue University Indianapolis (IUPUI) / The aging infrastructure of a wastewater collection system can leak, capture ground water, and capture precipitation runoff. These are some of the most common problems in many of today’s US collection systems and are often collectively referred to as Rain Derived Inflow and Infiltration (RDII or I/I). The goal of this study is to investigate such optimized methods and their potential to improve flow monitor placement, especially for RDII studies, and to improve upon Stevens (2005) methodology. This project adopts a methodology from the “facility location problem”, a branch of operations research and graph theory. Solutions to a facility location problem will be adapted and utilized within a transportation GIS application to determine optimal placement.

This dissertation will specifically address the issue of improving the quality of satellite scatterometer retrieved ocean surface vector winds (OVW), especially in the presence of strong rain associated with tropical cyclones. A novel active/passive OVW retrieval algorithm is developed that corrects Ku-band scatterometer measurements for rain effects and then uses them to retrieve accurate OVW. The rain correction procedure makes use of independent information available from collocated multi-frequency passive microwave observations provided by a companion sensor and also from simultaneous C-band scatterometer measurements. The synergy of these active and passive measurements enables improved correction for rain effects, which enhances the utility of Ku-band scatterometer measurements in extreme wind events. The OVW retrieval algorithm is based on the next generation instrument conceptual design for future US scatterometers, i.e. the Dual Frequency Scatterometer (DFS) developed by NASA’s Jet Propulsion Laboratory. Under this dissertation research, an end-to-end computer simulation was developed to evaluate the performance of this active/passive technique for retrieving hurricane force winds in the presence of intense rain. High-resolution hurricane wind and precipitation fields were simulated for several scenes of Hurricane Isabel in 2003 using the Weather Research and Forecasting (WRF) Model. Using these numerical weather model environmental fields, active/passive measurements were simulated for instruments proposed for the Global Change Observation Mission- Water Cycle (GCOM-W2) satellite series planned by the Japanese Aerospace Exploration Agency. Further, the quality of the simulation was evaluated using actual hurricane measurements from the Advanced Microwave Scanning Radiometer and iv SeaWinds scatterometer onboard the Advanced Earth Observing Satellite-II (ADEOS-II). The analysis of these satellite data provided confidence in the capability of the simulation to generate realistic active/passive measurements at the top of the atmosphere. Results are very encouraging, and they show that the new algorithm can retrieve accurate ocean surface wind speeds in realistic hurricane conditions using the rain corrected Ku-band scatterometer measurements. They demonstrate the potential to improve wind measurements in extreme wind events for future wind scatterometry missions such as the proposed GCOM-W2.

M. S.

by Ng Wing-Sze Cecilia. / Thesis (M.B.A.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 92-93). / ABSTRACT --- p.ii / TABLE OF CONTENT --- p.iii / CHAPTER / Chapter 1. --- COMPANY PROFILE --- p.1 / The Walt Disney Parks --- p.1 / Hong Kong Disneyland --- p.1 / Location --- p.1 / Park Developer & Operator --- p.2 / Financing --- p.2 / Infrastructure --- p.3 / Schedule of Operation --- p.4 / Chapter 2. --- HONG KONG DISNEYLAND BUSINESS MODEL --- p.6 / Revenue Model --- p.7 / Customer Base --- p.7 / Pricing Strategy --- p.8 / Financial Performance Variable --- p.9 / Risk Management Program --- p.10 / The Walt Disney Company Risk Management --- p.10 / HKDL Risk Management --- p.13 / Risk Management on Book Record --- p.13 / Chapter 3. --- PRECIPITATION RISK EXPOSURE --- p.15 / Introduction to Precipitation --- p.15 / Distinguish between Weather and Climate --- p.16 / Rainfall Risk Exposure --- p.16 / Precipitation in Hong Kong --- p.17 / Overview --- p.17 / Rainstorm Warning System --- p.18 / Practices on Rainy Days --- p.20 / Theme Park Industry --- p.20 / The Ocean Park --- p.21 / Rainfall Risk Mitigation --- p.21 / Chapter 4. --- WEATHER DERIVATIVES --- p.24 / Evolution --- p.24 / The Birth of Weather Derivatives --- p.24 / Weather Risk Management Association --- p.24 / Year 1999 --- p.25 / Year 2000 --- p.25 / Year 2001 --- p.26 / Year 2002 --- p.26 / Precipitation Derivatives --- p.27 / Market & Market Players --- p.28 / Types of Product --- p.30 / Index Derivatives --- p.30 / Event-Basis Derivatives --- p.32 / Chapter 5. --- Hedging Against Rainfall Risk with Weather Derivatives --- p.33 / Formation of Hedging Strategy --- p.34 / Hedging Objectives --- p.34 / Hedging Target --- p.35 / Dimension of Precipitation Impacts --- p.35 / Normal Revenue without Rainfall Risk --- p.40 / Revenue Forecasting for Year 1 --- p.41 / Specifications on the Contracts --- p.46 / Chapter 6. --- General Recommendations to HKDL for hedging with all kinds of Rainfall Derivatives --- p.49 / Choice of Market and Counter Parties --- p.49 / Index Model Design --- p.50 / Dimensions of Variables & Time Scale --- p.50 / Accumulated Rainfall Index --- p.51 / Methodologies of Rainfall Measurements --- p.54 / Location of Rainfall Measuring Stations --- p.54 / Measuring Instrument --- p.56 / Historical Data Consistency --- p.58 / Data Availability and Reliability --- p.59 / Choice of Strike Level --- p.59 / Tick Size and Maximum Payments --- p.62 / Pricing Approach --- p.63 / Chapter 7. --- Example of Rainfall Derivatives --- p.66 / Black/Red Rainstorm Signal Call --- p.66 / Specifications --- p.66 / Revenue model under Different Scenario --- p.68 / Chapter 8. --- Portfolio Management --- p.70 / Risk Management Information System --- p.70 / Issues on Book Keeping --- p.71 / Chapter 9. --- CONCULSION --- p.72