Rainfall data are usually gathered at daily timescales due to the availability of daily rain-gauges throughout the world. However, rainfall data at fine timescale are required for certain hydrologic modellings such as crop simulation modelling, erosion modelling etc. Limited availability of such data leads to the option of daily rainfall disaggregation. This research investigates the use of a stochastic rainfall disaggregation model on a regional basis to disaggregate daily rainfall into any desired fine timescale in the State of Queensland, Australia. With the incorporation of seasonality into the variance relationship and capping of the fine timescale maximum intensities, the model was found to be a useful tool for disaggregating daily rainfall in the regions of Queensland. The degree of model complexity in terms of binary chain parameter calibration was also reduced by using only three parameters for Queensland. The resulting rainfall Intensity-Frequency-Duration (IFD) curves better predicted the intensities at fine timescale durations compared with the existing Australian Rainfall and Runoff (ARR) approach. The model has also been linked to the SILO Data Drill synthetic data to disaggregate daily rainfall at sites where limited or no fine timescale observed data are available. This research has analysed the fine timescale rainfall properties at various sites in Queensland and established sufficient confidence in using the model for Queensland.

Severe flooding events in recent years have underlined the importance of accurate hydrological modelling in urban areas. There are many important parameters relating to both the rainfall distribution and properties of the land on which the rain falls that controls the impacts of the rain event. While the importance of input parameters such as initial water content, topography and extent of hardened surfaces is widely known, their impact on hydrological response in urban areas is not thoroughly understood. In 2017, scientists from the Swedish Meteorological and Hydrological Institute, SMHI, presented five empirical hyetographs based on long-term Swedish municipal rain data (Olsson, et al., 2017). The hyetographs vary in location of peak and distribution of intensity. Olsson (2019) evaluated the hydrological response in terms of water depth of the hyetographs in relation to Chicago Design Storm (CDS), a common design storm used in Swedish hydrological modelling, and found that CDS nearly always overestimates the hydrological response in comparison to the empirical hyetographs, meaning historical rainfall intensity distributions, developed by SMHI.  The aim of this thesis is to analyse the robustness of empirical hyetographs by conducting a sensitivity analysis of a generic urban model with a variation of input parameters. A statistical analysis of data on hardened surfaces, topography and initial water content was conducted to find the median, 5th and 95th percentile respectively of the range of values in Swedish conditions. These values were applied to a synthetic urban model and run together with the five empirical hyetographs and CDS in MIKE 21. The results indicate that the empirical hyetographs are not very robust relating to variations in infiltration capacity (initial water content and amount of hardened areas), while they are more robust when varying the topography. The variation of topography also resulted in large variations in water depth, time to peak and extent of flooded area, while variation of initial water content and amount of hardened surfaces had smaller, although still clear, effects. Furthermore, the results show that hyetographs with a late peak are more sensitive to variations in initial water content and hardened surfaces than hyetographs with an early peak. On average, CDS estimates the response in comparison to the empirical hyetographs accurately, with an average overestimation of 0.5%, but does not capture the range and complexity of the empirical hyetographs. Including the frequency of the different hyetographs, CDS gave an overestimation of 5% compared to the empirical hyetographs. The highlight the uncertainty in using CDS as input for urban cloudburst modelling, but limitations in form of catchment properties in a study area and the importance of the input values limits the generability of the study. / De senaste årens allvarliga översvämningshändelser har understrukit vikten av noggrann hydrologisk modellering i stadsområden. Även om betydelsen av parametrar som initial vattenmättnad, topografi och andelen hårdgjorda ytor är allmänt känd, är deras inverkan på urban hydrodynamisk modellering inte helt klarlagd. Under 2017 presenterade forskare från Sveriges Meteorologiska och Hydrologiska Institut, SMHI, fem empiriska hyetografer baserade på långvariga kommunala regndata (Olsson et al., 2017). Hyetograferna varierar i fördelning av intensitet och tidsmässig placering av maxintensitet. Olsson (2019) utvärderade hyetografernas hydrologiska respons i relation till Chicago Design Storm (CDS), en vanlig designstorm som används i svensk hydrologisk modellering, och fann att CDS nästan alltid överskattar responsen i jämförelse med de empiriska hyetograferna.  Syftet med detta examensarbete är att analysera robustheten hos de empiriska hyetograferna genom att utföra en känslighetsanalys av en generisk stadsmodell med en variation av ingångsparametrar. En statistisk analys av data om hårdgjorda ytor, topografi och initial vattenmättnad genomfördes för att hitta median, 5:e respektive 95:e percentilen av värdena i svenska förhållanden. Dessa värden applicerades på en generisk stadsmodell och kördes tillsammans med de fem empiriska hyetograferna och CDS i MIKE 21. Resultaten indikerar att de empiriska hyetograferna inte är helt robusta vad gäller variationer i infiltrationskapacitet (initial vattenmättnad och andel hårdgjorda ytor), medan de är mer robusta vid variation av topografin. Variationen av topografi resulterade också i stora variationer i vattendjup, tid till maxflöde och utbredning av översvämmat område, medan variation av initial vattenmättnad och mängden hårdgjorda ytor hade mindre, men fortfarande tydliga, effekter. Vidare visar resultaten att hyetografer med sen topp är känsligare för variationer i initial vattenhalt och hårdgjorda ytor än hyetografer med tidig topp. I genomsnitt uppskattar CDS responsen från de empiriska hyetograferna korrekt, med en genomsnittlig överskattning på 0.5%, men fångar inte omfånget och komplexiteten hos de empiriska hyetograferna. Inräknat frekvensen av de olika hyetograferna gav CDS en överskattning på 5 % jämfört med de empiriska hyetograferna. Resultaten belyser osäkerheterna i att använda CDS regn som drivdata i skyfallsmodelleringar för stadsplanering, men begränsningar i form av markegenskaper i ett enskilt studieområde och vikten av modellens initialvärden begränsar dock generaliteten för studien.

Esta pesquisa tem como finalidade discutir os impactos da variabilidade espacial e temporal de precipitações intensas nas vazões de cursos d\'água em bacias urbanizadas mediante a análise de dados históricos da pluviometria obtidos durante eventos críticos. A bacia hidrográfica do rio Tietê, em sua porção mais urbanizada, é a área objeto deste estudo. Após uma revisão sobre o tema na literatura específica, foram desenvolvidas chuvas de projeto com os padrões observados e com padrões teóricos, frequentemente utilizados na geração das tormentas sintéticas. O volume total precipitado foi associado ao período de retorno (TR) de 100 anos, a partir da análise estatística de chuvas pontuais e pela aplicação de fatores de redução de área (FRA) observados na área em estudo e de outras regiões, que vêm sendo utilizados em projetos de drenagem, sem qualquer estudo de validação; o intuito foi o de demonstrar a importância da definição de FRA específicos, a fim de evitar superdimensionamentos e otimizar as soluções. As chuvas de projeto foram aplicadas num modelo matemático de transformação chuva-vazão, devidamente calibrado, para obtenção das vazões de projeto resultantes no limite de jusante da bacia hidrográfica, frente aos diferentes padrões de solicitações hidrológicas. Para auxiliar a calibração do modelo estavam disponíveis dados dos postos telemétricos do Sistema de Alerta a Inundações de São Paulo - SAISP, curvas-chave e, para melhor representação dos eventos de precipitação observados, pode-se contar com as imagens do radar de Ponte Nova, em complementação às informações da rede de superfície. A comparação dos resultados obtidos no modelo hidrológico mostrou que os efeitos dos parâmetros variáveis (volume, distribuição espacial e temporal) são expressivos na composição dos hidrogramas de projeto. Dos testes realizados, identificaram-se as situações mais e menos críticas para a bacia, em termos de distribuição espacial e temporal e duração da chuva de projeto, além de estabelecer as diferenças no dimensionamento do sistema de drenagem pela adoção de FRA específico. Concluiu-se que, pela metodologia proposta, é possível chegar a vazões máximas de projeto apenas pela simulação de tormentas sintéticas, com diferenças de 10% a 20% das tormentas observadas maximizadas. Há, no entanto, a necessidade de realização de estudos adicionais, tanto para definição dos valores de FRA específicos, quanto de simulação de quantidade maior de padrões críticos observados, para a aplicação prática das indicações desse estudo com maior confiabilidade. / This research aims to discuss the impact of the spatial and temporal variability of heavy rainfall in the river flows in urbanized catchments by the historical rainfall data analysis obtained during critical events. The Tiete River catchment, in its most urbanized portion, is the subject of study of this research. After a review of the subject in the specific literature, design rainfall was developed along with the observed and theoretical patterns, often used in the generation of synthetic storms. The total volume precipitated was associated with the 100 years return period (RP), from the statistical analysis of point rainfall and for the application of areal reduction factors (ARF) observed in the study area and in other regions, which have been used in drainage projects without any validation study; the intention was to demonstrate the importance of the definition of specific ARF, in order to avoid oversizing and optimizing solutions. The design precipitation was applied on rainfall-runoff mathematical model, properly calibrated, so as to obtain the resulting design flow at the downstream boundary of the catchment, facing the different patterns of hydrological solicitations. In order to assist the calibration of the model, available data has been used from telemetric stations of the Sistema de Alerta a Inundações de São Paulo (São Paulo Flooding Alert System) - SAISP, discharge curves, and for better representation of the observed precipitation events, can be counted on the images taken from the Ponte Nova radar, as a complement to the information from the surface network. The comparison of the results of the hydrological model has shown that the effects of the variable parameters (volume, spatial and temporal distributions) are significant in the composition of the design hydrograph. Out of the performed tests, the most and the least critical situations were identified concerning the catchment in terms of both spatial and temporal distribution as well as the duration of the design storm. Also, the differences in the dimensions of the of the drainage system design were established by the adoption of specific ARF. Thus, it has been concluded, according to the proposed methodology, that it is possible to reach maximum design flow just by simulating synthetic storms, with differences ranging from 10% to 20% of the observed storms maximized. However, there is a need for additional studies, either to set up setting specific values of ARF or to simulate a larger quantity of critical patterns observed, in order to apply the indications of this study with higher reliability.

Esta pesquisa tem como finalidade discutir os impactos da variabilidade espacial e temporal de precipitações intensas nas vazões de cursos d\'água em bacias urbanizadas mediante a análise de dados históricos da pluviometria obtidos durante eventos críticos. A bacia hidrográfica do rio Tietê, em sua porção mais urbanizada, é a área objeto deste estudo. Após uma revisão sobre o tema na literatura específica, foram desenvolvidas chuvas de projeto com os padrões observados e com padrões teóricos, frequentemente utilizados na geração das tormentas sintéticas. O volume total precipitado foi associado ao período de retorno (TR) de 100 anos, a partir da análise estatística de chuvas pontuais e pela aplicação de fatores de redução de área (FRA) observados na área em estudo e de outras regiões, que vêm sendo utilizados em projetos de drenagem, sem qualquer estudo de validação; o intuito foi o de demonstrar a importância da definição de FRA específicos, a fim de evitar superdimensionamentos e otimizar as soluções. As chuvas de projeto foram aplicadas num modelo matemático de transformação chuva-vazão, devidamente calibrado, para obtenção das vazões de projeto resultantes no limite de jusante da bacia hidrográfica, frente aos diferentes padrões de solicitações hidrológicas. Para auxiliar a calibração do modelo estavam disponíveis dados dos postos telemétricos do Sistema de Alerta a Inundações de São Paulo - SAISP, curvas-chave e, para melhor representação dos eventos de precipitação observados, pode-se contar com as imagens do radar de Ponte Nova, em complementação às informações da rede de superfície. A comparação dos resultados obtidos no modelo hidrológico mostrou que os efeitos dos parâmetros variáveis (volume, distribuição espacial e temporal) são expressivos na composição dos hidrogramas de projeto. Dos testes realizados, identificaram-se as situações mais e menos críticas para a bacia, em termos de distribuição espacial e temporal e duração da chuva de projeto, além de estabelecer as diferenças no dimensionamento do sistema de drenagem pela adoção de FRA específico. Concluiu-se que, pela metodologia proposta, é possível chegar a vazões máximas de projeto apenas pela simulação de tormentas sintéticas, com diferenças de 10% a 20% das tormentas observadas maximizadas. Há, no entanto, a necessidade de realização de estudos adicionais, tanto para definição dos valores de FRA específicos, quanto de simulação de quantidade maior de padrões críticos observados, para a aplicação prática das indicações desse estudo com maior confiabilidade. / This research aims to discuss the impact of the spatial and temporal variability of heavy rainfall in the river flows in urbanized catchments by the historical rainfall data analysis obtained during critical events. The Tiete River catchment, in its most urbanized portion, is the subject of study of this research. After a review of the subject in the specific literature, design rainfall was developed along with the observed and theoretical patterns, often used in the generation of synthetic storms. The total volume precipitated was associated with the 100 years return period (RP), from the statistical analysis of point rainfall and for the application of areal reduction factors (ARF) observed in the study area and in other regions, which have been used in drainage projects without any validation study; the intention was to demonstrate the importance of the definition of specific ARF, in order to avoid oversizing and optimizing solutions. The design precipitation was applied on rainfall-runoff mathematical model, properly calibrated, so as to obtain the resulting design flow at the downstream boundary of the catchment, facing the different patterns of hydrological solicitations. In order to assist the calibration of the model, available data has been used from telemetric stations of the Sistema de Alerta a Inundações de São Paulo (São Paulo Flooding Alert System) - SAISP, discharge curves, and for better representation of the observed precipitation events, can be counted on the images taken from the Ponte Nova radar, as a complement to the information from the surface network. The comparison of the results of the hydrological model has shown that the effects of the variable parameters (volume, spatial and temporal distributions) are significant in the composition of the design hydrograph. Out of the performed tests, the most and the least critical situations were identified concerning the catchment in terms of both spatial and temporal distribution as well as the duration of the design storm. Also, the differences in the dimensions of the of the drainage system design were established by the adoption of specific ARF. Thus, it has been concluded, according to the proposed methodology, that it is possible to reach maximum design flow just by simulating synthetic storms, with differences ranging from 10% to 20% of the observed storms maximized. However, there is a need for additional studies, either to set up setting specific values of ARF or to simulate a larger quantity of critical patterns observed, in order to apply the indications of this study with higher reliability.

With an intensification of heavy rain events in a changing climate and a rapid urbanization the risk for pluvial flooding is increasing in our societies. Pluvial flooding, which is formed when the rainfall rate exceeds the infiltration or drainage rate, can occur rapidly and cause great damages, large economic losses and possibly risk human lives. This kind of flooding is difficult to predict since it is caused by short-term and often local processes, but preventive measures and more robust infrastructure developed over the last decades have decreased the risk of the most severe damages. One way to prevent damage is to map risk areas and take measures by performing a cloudburst modelling, which can be done as a 2D hydraulic modelling. Common practice in cloudburst modelling today is to use a uniform design storm, often the Chicago Design Storm (CDS), with the same hyetograph applied evenly over the whole model area. Even though rain is not spatially uniform this assumption might be valid for more stratiform frontal rain. Intense rain events however have a higher spatial variation in rain intensity, and an assumption like this might significantly affect the results. This study aimed to investigate the effect of the spatial variation in rain intensity on the modelled hydraulic response from an intense rain event. It was performed through a case study of the cloudburst in Gävle, Sweden, in August 2021. A 2D hydraulic model of the city was prepared in the software MIKE 21 Flow Model FM and the cloudburst event was simulated with a spatially varied rainfall input, based on radar data from the event with a 2x2 km resolution, and with spatially uniform rainfall input both with the temporal variation in rain intensity from the event and with a Chicago Design Storm, all with the same total volume. The scenarios were evaluated in terms of proportion of the model area being flooded, the average maximum flooding depth and by mapping the difference in flooding depth over the whole area. The results showed that the spatial variation of rainfall input had a significant effect on the hydraulic response in the city and that assuming a uniform rainfall might lead to an underestimation of the flooding depths in parts of the model area compared to a varied one. The average flooding depth was only a few percent higher for the spatially varied rain compared to the uniform rain with a similar time variation, but in large central areas of the city the model with the uniform rain underestimated the maximum flooding depth by 5-35%. The uniform CDS rain was seen to both over- and underestimate the flooding depth, but in the central and flooded parts of the city underestimation dominated. This points out a risk of using uniform design storms in cloudburst modelling, since a spatially varied rain of the same volume could give more severe effects than the simulated response and that using a uniform design storm potentially introduces an uncertainty in the modelled results that could be important to point out and further quantify. / Med en intensifiering av häftiga regnväder i ett förändrat klimat och en allt snabbare urbanisering ökar risken för pluviala översvämningar i våra samhällen. Pluviala översvämningar, som skapas av att regnintensiteten är högre än infiltrations- eller dräneringshastigheten, kan uppstå plötsligt och orsaka stora skador, ekonomiska förluster och även i värsta fall riskera människoliv. Denna typ av översvämning är svår att förutse eftersom den orsakas av snabba och ofta lokala processer, men förebyggande åtgärder och mer robust infrastruktur som har utvecklats de senaste decennierna har minskat risken för de allvarligaste skadorna. Ett sätt att förebygga skador är att kartera riskområden genom skyfallsmodellering, till exempel med en tvådimensionell hydraulisk modell. Praxis idag är att använda spatialt uniforma typregn vid skyfallsmodellering, där samma hyetograf appliceras jämnt över hela modellområdet. Detta antagande kan ge giltiga resultat för mer stratiforma frontregn, men intensiva regn, skyfall, har generellt sett en hög spatial variation i intensiteten vilket gör att antagandet skulle kunna påverka resultatet signifikant. Denna studie syftade till att undersöka effekten av den spatiala variationen i regnintensitet på den simulerade hydrauliska responsen från ett intensivt regn och den utfördes som en fallstudie av skyfallet i Gävle 17-18 augusti 2021. En 2D hydraulisk modell av Gävle förbereddes i programmet MIKE 21 Flow Model FM och simuleringar utfördes med en spatialt varierad regnindata, baserad på radardata från tillfället med en 2x2 km upplösning, och med spatialt uniforma regnindata både med den verkliga tidsvariationen och med en Chicago Design Storm (CDS), alla med samma totala volym. Skillnaden mellan scenarierna utvärderades genom att jämföra andel översvämmat modellområde, medel av maximala översvämningsdjupet och en kartering av skillnaden i översvämningsdjup över hela modellområdet. Resultaten visade att den spatiala variationen i regnindatan hade en signifikant effekt på den simulerade hydrauliska responsen i staden och att antagande om uniform regnintensitet kan leda till en underskattning av översvämningsdjupen i modellområdet jämfört med ett varierat regn. Medelvärdet av översvämningsdjupet var endast några procent högre  för det spatialt varierade regnet, men i stora centrala områden underskattade modellen med det uniforma regnet det maximala översvämningsdjupet med 5-35 %. Det uniforma CDS-regnet både under- och överskattade översvämningsdjupet, men i centrala och översvämmade områden var det större delar som underskattades. Detta visar på en risk med att använda uniforma typregn i skyfallsmodellering, då ett spatialt varierat regn med samma volym skulle kunna ge betydligt allvarligare effekter än de som modellen har visat och att användandet av uniforma testregn potentiellt inför en osäkerhet i resultaten som är viktig att poängtera och även att vidare undersöka och kvantifiera.