Edge effect causes apparent fractal correlation dimension of uniform spatial raindrop distribution

Lovejoy and Schertzer (1990a) presented a statistical analysis of blotting paper observations of the (twodimensional) spatial distribution of raindrop stains. They found empirical evidence for the fractal scaling behavior of raindrops in space, with potentially far-reaching implications for rainfall microphysics and radar meteorology. In particular, the fractal correlation dimensions determined from their blotting paper observations led them to conclude that “drops are (hierarchically) clustered” and that “inhomogeneity in rain is likely to extend down to millimeter scales”. Confirming previously reported Monte Carlo simulations, we demonstrate analytically that the claims based on this analysis need to be reconsidered, as fractal correlation dimensions similar to the ones reported (i.e. smaller than the value of two expected for uniformly distributed raindrops) can result from instrumental artifacts (edge effects) in otherwise homogeneous Poissonian rainfall. Hence, the results of the blotting paper experiment are not statistically significant enough to reject the Poisson homogeneity hypothesis in favor of a fractal description of the discrete nature of rainfall. Our analysis is based on an analytical expression for the expected overlap area between a circle and a square, when the circle center is randomly (uniformly) distributed inside the square. The derived expression ( r2−8r3/3+r4/2, where r denotes the ratio between the circle radius and the side of the square) can be used as a reference curve against which to test the statistical significance of fractal correlation dimensions determined from spatial point patterns, such as those of raindrops and rainfall cells.Postprint (published version

Effects of Increased Wind Power Generation on Mid-Norway’s Energy Balance under Climate Change: A Market Based Approach

Thanks to its huge water storage capacity, Norway has an excess of energy generation at annual scale, although significant regional disparity exists. On average, the Mid-Norway region has an energy deficit and needs to import more electricity than it exports. We show that this energy deficit can be reduced with an increase in wind generation and transmission line capacity, even in future climate scenarios where both mean annual temperature and precipitation are changed. For the considered scenarios, the deficit observed in winter disappears, i.e., when electricity consumption and prices are high. At the annual scale, the deficit behaviour depends more on future changes in precipitation. Another consequence of changes in wind production and transmission capacity is the modification of electricity exchanges with neighbouring regions which are also modified both in terms of average, variability and seasonality

A modeling approach to assess the hydrological response of small mediterranean catchments to the variability of soil characteristics in a context of extreme events

This paper presents a modeling study aiming at quantifying the possible impact of soil characteristics on the hydrological response of small ungauged catchments in a context of extreme events. The study focuses on the September 2002 event in the Gard region (South-Eastern France), which led to catastrophic flash-floods. The proposed modeling approach is able to take into account rainfall variability and soil profiles variability. Its spatial discretization is determined using Digital Elevation Model (DEM) and a soil map. The model computes infiltration, ponding and vertical soil water distribution, as well as river discharge. In order to be applicable to ungauged catchments, the model is set up without any calibration and the soil parameter specification is based on an existing soil database. The model verification is based on a regional evaluation using 17 estimated discharges obtained from an extensive post-flood investigation. Thus, this approach provides a spatial view of the hydrological response across a large range of scales. To perform the simulations, radar rainfall estimations are used at a 1 km<sup>2</sup> and 5 min resolution. To specify the soil hydraulic properties, two types of pedotransfer function (PTF) are compared. It is shown that the PTF including information about soil structure reflects better the spatial variability that can be encountered in the field. The study is focused on four small ungauged catchments of less than 10 km<sup>2</sup>, which experienced casualties. Simulated specific peak discharges are found to be in agreement with estimations from a post-event in situ investigation. Examining the dynamics of simulated infiltration and saturation degrees, two different behaviors are shown which correspond to different runoff production mechanisms that could be encountered within catchments of less than 10 km<sup>2</sup>. They produce simulated runoff coefficients that evolve in time and highlight the variability of the infiltration capacity of the various soil types. Therefore, we propose a cartography distinguishing between areas prone to saturation excess and areas prone only to infiltration excess mechanisms. The questions raised by this modeling study will be useful to improve field observations, aiming at better understanding runoff generation for these extreme events and examine the possibility for early warning, even in very small ungauged catchments

Gestion optimale d'un réservoir hydraulique multiusages et changement climatique. Modèles, projections et incertitudes (Application à la réserve de Serre-Ponçon)

Pouvoir évaluer l'impact du changement climatique sur la ressource en eau, et les systèmes de gestion qui lui sont associés, est une préoccupation majeure de nos sociétés. Une telle évaluation nécessite la mise en place d'une chaîne de simulation qui permet, sur la base d'expériences climatiques futures, i) d'estimer à l'échelle régionale l'évolution possible de la ressource et de sa variabilité, ii) de simuler le comportement des systèmes utilisés pour leur gestion pour iii) estimer les éventuelles modifications de performance. Cette thèse vise à tester la possibilité de mettre en place une chaîne de simulation de ce type pour un système de gestion réel et à identifier quelles sont les composantes à considérer dans ce cas. Pour ce faire, nous chercherons en particulier à apporter des éléments de réponse aux questions suivantes: - Quelles représentations peut-on faire d'un système de gestion opérationnel pour une application en climat modifié ? - Quels éléments d'évaluation peuvent permettre d'estimer l'impact du changement climatique sur ce système de gestion ? - Quelles sont les sources d'incertitudes influençant cette évaluation ? Quelles sont les contributions relatives à l'incertitude totale des différentes méthodes et modèles utilisés ? Nous considérerons plus précisément le système de gestion du barrage de Serre-Ponçon, alimenté par le haut bassin versant de la Durance. Ce barrage, géré par EDF, est l'un des plus grands barrages artificiels européens. Il est multi-usages (irrigation, soutien d'étiage, production d'hydroélectricité, tourisme). Dans un premier temps, nous présenterons le contexte du système de gestion actuel. Nous mettrons ensuite en place un modèle de gestion du barrage visant à reproduire de façon réaliste du point de vue du gestionnaire actuel (EDF), mais simplifiée pour pouvoir être appliqué sous scénarios futurs - la gestion actuelle du barrage. Nous développerons pour cela i) des modèles permettant d'estimer les différentes demandes en eau et ii) un modèle d'optimisation de la gestion sous contraintes. Ce modèle permettra de simuler la gestion du système au pas de temps journalier sur plusieurs décennies du climat récent, ou de climats futurs modifiés. Nous proposerons ensuite un ensemble d'indicateurs qui permettent de fournir une estimation de la performance d'un tel système à partir des sorties du modèle de gestion obtenues par simulation pour différentes périodes de 30 ans. Nous explorerons la façon dont la performance estimée dépend du modèle choisi pour la représentation du système de gestion actuel, et plus précisément de la façon dont la stratégie utilisée pour l'optimisation de la gestion est élaborée. A ce titre, nous proposerons trois modèles de gestion basés sur trois types de stratégies, obtenues pour des degrés différents de prévisibilité des apports et sollicitations futurs à la retenue. Pour ces simulations, les modèles d'impacts nécessitent des scénarios de forçages météorologiques à l'échelle de bassin versant (e.g. modèle hydrologique, modèle d'usages de l'eau, modèle de gestion de la ressource). Ces scénarios peuvent être obtenus par des méthodes de descente d'échelle statistique (MDES), sur la base des simulations grande échelle des modèles climatiques globaux. Enfin, nous évaluerons les incertitudes liées aux deux types de modèles et estimerons leurs contributions relatives à l'incertitude globale. Nous utiliserons pour cela les scénarios issus de différentes chaines de simulation GCM/MDES produits sur la période 1860-2011 dans le cadre du projet RIWER2030. Nous montrerons que ces deux sources d'incertitudes sont du même ordre de grandeur sur l'estimation des modifications de performance.Assess the impact of climate change on water resources and management systems associated, is a major concern of our society. This requires the establishment of a simulation chain which allows, on the basis of future climate experiments i) to estimate the possible changes in regional resource and its variability, ii) to simulate the behavior of the systems used to manage them in order to iii) estimate the possible changes in performance. This thesis aims to test the feasibility of establishing a chain simulation of such a management system to identify what are the real components to consider in this case. To do this, we have to provide answers to the following questions: - How can we represent an operational management system in a climate change context? - What elements of evaluation can be used to estimate the impact of climate change on the management system? - What are the sources of uncertainty influencing this assessment? What are the relative contributions to the total uncertainty of these different methods and models used? We consider the system of management of the reservoir of Serre-Ponçon, built on the high basin of the Durance. This dam, operated by EDF, is one of the largest artificial dams Europe. It is multi-purpose (irrigation, low-flow support, hydropower, tourism). As a first step, we will present the context of the current management system. Then, we will establish a management model to reproduce - in a realistic way from the point of view of the current manager (EDF), but simplified to be applied in future scenarios - the current management of the Serre-Ponçon reserve. We will develop for this, i) different models to estimate different water demands and ii) an optimization model with constraints management. This model will simulate the management system in daily time step on several decades of recent climate or future climate change. We then propose a set of indicators to provide an estimate of the performance of such a system from the outputs of the management model obtained by simulation for different periods of 30 years. We will explore how the estimated performance depends on the model chosen to represent the current management system, and more specifically how the strategy used to optimize the management is developed. To this end, we will propose three management models based on three types of strategies, obtained for different degrees of predictability of future inflows and constraints. For these simulations, the impact models require meteorological forcing scenarios at watershed scale (eg hydrological model, model of water use model of resource management). These scenarios can be obtained by statistical downscaling methods (SDM), on the basis of large-scale simulations of global climate models. Finally, we will evaluate the uncertainties associated with the two types of models and will estimate their relative contributions to the overall uncertainty. We have used this scenario from different GCM/SDM simulations over the period 1860-2100 obtained within the RIWER2030 project. We show that these two sources of uncertainty are of the same order of magnitude estimate of changes in performance.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF