The primary focus of this thesis is to describe the prevailing atmospheric conditions when heavy rainfall occurs over the Gauteng Province in South Africa. This thesis first describes the characteristics of daily heavy rainfall over Gauteng by defining different heavy rainfall classes and considering the seasonal distribution of these events. Late summer (January, February and March) has considerably more heavy rainfall days than early summer. The change of the character of the atmosphere as the summer season progresses is highlighted by the investigation into the monthly average synoptic circulation patterns when heavy rainfall occurs. The weather systems change from extra-tropical in the first few months of the summer rainfall season to tropical in February months. It is also shown how cyclonic vorticity advection occurs in the upper troposphere whenever heavy rainfall occurs, irrespective of the time of the season. A deep layer of horizontal wind convergence is also present when heavy rainfall occurs and this is replaced by horizontal wind divergence above that. A monthly climatology of sounding-derived parameters associated with heavy rainfall is constructed and it is again apparent how the atmosphere changes from one where conditional instability dominates the production of heavy rainfall in early summer to one where convective instability plays a dominant role in late summer. Twelve sounding-derived variables are identified to describe the thermodynamical profile of the atmosphere when heavy rainfall occurs over Gauteng. They include variables not previously used such as the Elevated K-Index and the meridionial wind component near the surface. Self-organizing maps are used to create a climatology of the vertical profile of the atmosphere during heavy rainfall and this methods captures the changes to the atmospheric state during the progression of the summer season. Favourable sounding-derived parameters and circulation criteria are combined in a self-organizing map to predict daily rainfall frequencies. This method produces encouraging results and methods should be explored to create probabilistic daily rainfall forecast for Gauteng in an operational environment. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Geography, Geoinformatics and Meteorology / unrestricted

Many studies have been done on synopticallyorced systems and heavy rainfall, but little research has gone into forecasting training convective storms. The research in this paper examines 38 separate synopticallyorced convective extreme precipitation training (SCEPT) events to find trends and consistencies in the synoptic environment. Three separate cases were found in which a SCEPT event occurred: Closed Upper-Level Trough (CULL), Upper-Level Trough (ULT), and 850 Trough/Low (850TL). Each event occurred in areas of precipitable water greater than 36.42 mm (1.43 inches), near maximums of 850 hPa moisture convergence and 700 hPa upper-vertical velocities, under the 850 hPa jet, and in the warm sector of a mid-latitude cyclone. CULL and ULT events occurred in strongly forced synoptic environments where 500 and 300 hPa troughs were evident and generally positively tilted. Little upper-level forcing, above 700 hPa, was found in 850TL events.

Diarrheal disease has long been known to be a burden to children worldwide. Although child mortality rates as a result of diarrhea have decreased over the past two decades, overall diarrhea incidence has remained relatively stable. In Cambodia, diarrhea was the third most prevalent outpatient diagnosis for children under five in 2012, with a reported incidence rate of 12 per 100 children, up from 7 per 100 children in 2008 (Ministry of Planning Cambodia, 2012). Cambodia is an agricultural country with 80% of the population living in rural areas (National Institute of Statistics Ministry of Planning, 2013). Many are also poor, with 20.5% of the population living at or below the poverty line (Sobrado et al., 2014). As a result, a large portion of the population is vulnerable to changing climate patterns and seasonal rainfalls. These patterns have been shown to have an effect on the incidence of diarrhea in regions throughout the world. This research evaluated the relationship between seasonality and the incidence of diarrheal disease in children under five years old in the Rumduol district, Svay Rieng province of Cambodia. Using monthly under-five diarrhea data from a local health center and meteorological data from the Ministry of Water Resources and Meteorology (MoWRAM), Spearman’s Correlation was used to find associations between monthly rainfall, heavy rainfall (defined by the 90th percentile), maximum average monthly temperature, and minimum average monthly temperature. Additionally, household surveys, interviews, and observations were used to understand how seasonal behavior, age/gender, household practices, and caregiver perception of the disease affect decisions surrounding diagnosis and treatment of childhood diarrhea throughout the year. Based on the results of the analysis, the number of heavy rainfall days had a weak negative association with monthly under-five diarrhea incidence in the initial month and following month, referred to as lag 0 and lag 1 (rs(96) = -.216, p = .035 and rs(95) = -.219, p = .033). Minimum average monthly temperature was also shown to have weak negative association with monthly under-five diarrhea incidence at lag 0 and lag 1 (rs(96) = -.208, p = .042 and rs(95) = -.212, p = .039). The negative correlation between heavy rainfall and under-five diarrhea indicates that heavy rain can have a washing effect on the environment at lag 0 and lag 1 months. Higher diarrhea incidence in the cooler months suggest a possible link to rotavirus, however more research must be done to make confirm this. Monthly rainfall was seen to have a positive association with diarrhea within the lag 3 and lag 4 months (rs(93) = .250, p = .015; rs(92) = .222, p = .034). This indicates that increased rainfall could have a delayed effect on diarrhea by three or four months. Maximum temperature did not have statistically significant results. These results show that heavy rainfall and minimum temperature likely play role in under-five child diarrhea in the study area at shorter lags times, while monthly rainfall has a greater effect at longer lag times. Results of survey and interview data showed participants had sufficient knowledge on personal and food hygiene practices but often practiced improper environmental hygiene behavior, especially as it related to the handling of child and animal feces. Additionally, there were statistically significant results when looking at the relationship between environmental hygiene knowledge and practice and households where mothers migrate for work. Households with migrant mothers was common within the study area, with 51.9% of households having a mother who was currently working away from home or had plans to return to work soon. More data is needed to further investigate this relationship; however, this result suggests that hygiene knowledge and practice could suffer in households where the mother is absent, as added burden is placed on grandmothers to do domestic and childcare work.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22048号 / 工博第4629号 / 新制||工||1722(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中北 英一, 准教授 山口 弘誠, 准教授 田中 賢治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Thesis (M. Sc. (Statistics)) -- University of Limpopo, 2020 / The main purpose of modelling rare events such as heavy rainfall, heat waves, wind speed, interest rate and many other rare events is to try and mitigate the risk that might arise from these events. Heavy rainfall and floods are still troubling many countries. Almost every incident of heavy rainfall or floods might result in loss of lives, damages to infrastructure and roads, and also financial losses. In this dissertation, the interest was in modelling average monthly rainfall for South Africa using extreme value theory (EVT). EVT is made up mainly of two approaches: the block maxima and peaks-over thresh old (POT). This leads to the generalised extreme value and the generalised Pareto distributions, respectively. The unknown parameters of these distri butions were estimated using the method of maximum likelihood estimators in this dissertation. According to goodness-of-fit test, the distribution in the Weibull domain of attraction, Gumbel domain and generalised Pareto distri butions were appropriate distributions to model the average monthly rainfall for South Africa. When modelling using the POT approach, the point process model suggested that some areas within South Africa might experience high rainfall in the coming years, whereas the GPD model suggested otherwise. The block maxima approach using the GEVD and GEVD for r-largest order statistics also revealed similar findings to that of the GPD. The study recommend that for future research on average monthly rainfall for South Africa the findings might be improved if we can invite the Bayesian approach and multivariate extremes. Furthermore, on the POT approach, time-varying covariates and thresholds are also recommended. / National Research Foundation (NRF) and South African Weather Service (SAWS)

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24208号 / 工博第5036号 / 新制||工||1786(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中北 英一, 准教授 山口 弘誠, 教授 田中 賢治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

of the doctoral dissertation Extreme precipitation is related to flooding which is one of the most frequent natural hazards in Central Europe. Detailed understanding of extreme precipitation is the precondition for an efficient risk management and more precise projections of precipitation, which include uncertainties, especially at regional scale. The thesis focuses on extreme precipitation in the Ore Mountains (OM) and the Vosges Mountains (VG); two low mountain ranges in Central Europe experiencing orographic effect on precipitation. Based on state of the art about precipitation in OM and VG, a currently missing analysis of the temporal distribution of precipitation in VG was needed prior to the analysis of extremes. The original dataset of daily precipitation totals from 14 weather stations used in the initial study was extended to 168 stations covering a broader area of VG. The study of temporal distribution of precipitation during 1960-2013 led to a classification of stations: (i) mountainous stations with winter maxima and highest mean annual totals due to orographic enhancement of precipitation, (ii) stations on leeward slopes with two maxima (summer and winter), (iii) lee side stations with summer maxima and lowest mean annual totals due to rain shadow and more continental character, and...

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24212号 / 工博第5040号 / 新制||工||1787(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中北 英一, 准教授 山口 弘誠, 准教授 佐山 敬洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Extreme Value Theory nds application in problems concerning low probability but high consequence events. In hydrology the study of heavy rainfall is important in regional ood risk assessment. In particular, the N-year return level is a key output of an extreme value analysis, hence care needs to be taken to ensure that the model is accurate and that the level of imprecision in the parameter estimates is made explicit. Rainfall is a process that evolves over time and space. Therefore, it is anticipated that at extreme levels the process would continue to show temporal and spatial correlation. In this study interest is in whether any trends in heavy rainfall can be detected for the Western Cape. The focus is on obtaining the 50-year daily winter rainfall return level and investigating whether this quantity is homogenous over the study area. The study is carried out in two stages. In the rst stage, the point process approach to extreme value theory is applied to arrive at the return level estimates at each of the fteen sites. Stationarity is assumed for the series at each station, thus an issue to deal with is that of short-range temporal correlation of threshold exceedances. The proportion of exceedances is found to be smaller (approximately 0.01) for stations towards the east such as Jonkersberg, Plettenbergbay and Tygerhoek. This can be attributed to rainfall values being mostly low, with few instances where large amounts of rainfall were observed. Looking at the parameters of the point process extreme value model, the location parameter estimate appears stable over the region in contrast to the scale parameter estimate which shows an increase towards in a south easterly direction. While the model is shown to t exceedances at each station adequately, the degree of uncertainty is large for stations such as Tygerhoek, where the maximum observed rainfall value is approximately twice as large as the high rainfall values. This situation was also observed at other stations and in such cases removal of these high rainfall values was avoided to minimize the risk of obtaining inaccurate return level estimates. The key result is an N-year rainfall return level estimate at each site. Interest is in mapping an estimate of the 50-year daily winter rainfall return level, however to evaluate the adequacy of the model at each site the 25-year return level is considered since a 25 year return period is well within the range of the observed data. The 25-year daily winter rainfall return level estimate for Ladismith is the smallest at 22:42 mm. This can be attributed to the station's generally low observed winter rainfall values. In contrast, the return level estimate for Tygerhoek is high, almost six times larger than that of Ladismith at 119:16 mm. Visually design values show di erences between sites, therefore it is of interest to investigate whether these di erences can be modelled. The second stage is the geostatistical analysis of the 50-year 24-hour rainfall return level The aim here is to quantify the degree of spatial variation in the 50-year 24-hour rainfall return level estimates and to use that association to predict values at unobserved sites within the study region. A tool for quantifying spatial variation is the variogram model. Estimation of the parameters of this model require a su ciently large sample, which is a challenge in this study since there is only fteen stations and therefore only fteen observations for the geostatistical analysis. To address this challenge, observations are expanded in space and time and then standardized and to create a larger pool of data from which the variogram is estimated. The obtained estimates are used in ordinary and universal kriging to derive the 50-year 24-hour winter rainfall return level maps. It is shown that 50-year daily winter design rainfall over most of the Western Cape lies between 40 mm and 80 mm, but rises sharply as one moves towards the east coast of the region. This is largely due to the in uence of large design values obtained for Tygerhoek. In ordinary kriging prediction uncertainty is lowest around observed values and is large if the distance from these points increases. Overall, prediction uncertainty maps show that ordinary kriging performs better than universal kriging where a linear regional trend in design values is included.

L’objectif principal de cette thèse est de s’intéresser aux fortes pluies dans les Monts Métallifères (OM) et les Vosges (VG) en Europe centrale. La méthode Weather Extremity Index a été appliquée sur les données de précipitation journalière de 167 stations dans les OM et 168 stations dans les VG et a permis de sélectionner les 54 plus forts évenements des précipitations extrêmes (EPEs) dans OM et VG. Plusieurs aspects des EPEs ont été examinés. Les résultats ont montré que les EPEs sont le plus souvent de courte durée (1—2 jours) dans les deux régions. Ils affectent une plus grande partie des OM que des VG. Les EPEs dans les VG apparaissent majoritairement lors de la situation synoptique d’un front froid ondulant ; dans les OM lors des cyclones générés par une goutte d’air froid isolé et dont le trajet est souvent qualifié de « Vb » (c.a.d. allant de la Méditerranée vers le nord-est). Toutefois deux des dix plus forts EPEs des VG sont apparus lors de situations de cyclones Vb. / The thesis focuses on extreme precipitation in the Ore Mountains (OM) and the Vosges Mountains (VG) in Central Europe. The Weather Extremity Index (WEI) was employed on daily precipitation totals from 167 stations in OM and 168 stations in VG. The WEI enabled to select the 54 strongest extreme precipitation events (EPEs) in OM and VG. Many characteristics of the EPEs were investigated in the thesis. The results showed that the EPEs lasted mostly 1—2 days in both regions, whereas affected a larger part of OM as compared to VG. Stationary fronts occurred most frequently during EPEs in VG, while lows in OM. Lows in OM during EPEs often originated from cold air cut-off and most of them had Vb track from Mediterranean towards the northeast. Even during two of the ten strongest EPEs in VG, the extreme precipitation was related to Vb lows, this time strongly deflected westwards.