Quantifying the rain heterogeneity by X-band radar measurements for improving flood forecasting

Abstract : The focus of this thesis was to bring a nonlinear geophysical approach to urban hydrology. It aimed the study of rainfall non-linearity scaling and intermittency, achieving a stochastic very short-range forecast (nowcast) method, as well as its application to hydrological processes in (semi-) urban environments. The overall hydrological modelling part concerned the Bièvre Valley, which is a 110 km2 semi-urbanized area in the southwest of Paris region. Therefore, three different studies were performed within this area using two hydrological models: the conceptually-based semi-distributed model InfoWorks CS over the total Bièvre catchment, and the physically-based fully-distributed model developed at École des Ponts ParisTech called Multi-Hydro over two sub-catchments. The main goals were to better understand the impacts of spatio-temporal variability of rainfall data by using two products (the Météo-France C-band radar data with a resolution of 1 km x 1 km x 5 min; and the ENPC DPSRI X-band radar data at a 250 m x 250 m x 3.41 min resolution) as input to the models, and to identify the capacities of each model to deal with better resolution data, such as the X-band one. Then, the obtained results demonstrate that the reliability of the hydrological simulations are intrinsically dependent on rainfall data features. Moreover, the X-band radar data could measure higher peaks of rainfall rates and the fully-distributed model was more sensitive to better resolution rainfall data. Afterwards, different weather rainfall radar data from completely different sites (Brazil, France, Japan) were statistically analysed and compared in order to improve the general comprehension of rainfall scaling behaviour. In addition, the Intersection Theorem was applied to highlight the impacts of spatial variability of a virtual rain gauge network. The latter was generated by considering the location of each Bièvre Valley sub-catchment mass centre. Thus, it was possible to identify that the fractality of the virtual network led to an important information loss of the rainfall fields, biasing their statistics. This indicates that the common process (largely found in literature) of radar data calibration using rain gauges should be properly take into account this fractality. Finally, a new stochastic nowcast approach was proposed, using the continuous in scale cascade Universal Multifractals (UM) model. This method was applied to weather rainfall radar data from the Brazilian Amazon region and Paris. Although it is still under development and needs some improvements, the first results obtained with this forecast model presented here in this thesis are really encouraging and once more corroborate to the need of high spatio-temporal resolution data to cope flash floods
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Igor da Silva Rocha Paz. Quantifying the rain heterogeneity by X-band radar measurements for improving flood forecasting. Environmental Engineering. Université Paris-Est, 2018. English. ⟨NNT : 2018PESC1025⟩. ⟨tel-01973994⟩

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