Politicians are more likely to forward constituent inquiries to the appropriate level if they are of the same party as the recipient

The UK has enjoyed a significant degree of multi-tiered governance since the introduction of the Scottish Parliament in 1999, with recent events suggesting this dynamic will intensify further. Here, Audrey André, Jonathan Bradbury, and Sam Depauw look at constituent correspondence patterns, and find that politicians are much more likely to forward correspondence to the appropriate level if they are of the same party as the recipient, creating blurred lines of accountability and increasing confusion for the constituent

Impact of rainfall spatial variability on Flash Flood Forecasting

According to the United States National Hazard Statistics database, flooding and flash flooding have caused the largest number of deaths of any weather-related phenomenon over the last 30 years (Flash Flood Guidance Improvement Team, 2003). Like the storms that cause them, flash floods are very variable and non-linear phenomena in time and space, with the result that understanding and anticipating flash flood genesis is far from straightforward. In the U.S., the Flash Flood Guidance (FFG) estimates the average number of inches of rainfall for given durations required to produce flash flooding in the indicated county. In Europe, flash flood often occurred on small catchments (approximately 100 km2) and it has been shown that the spatial variability of rainfall has a great impact on the catchment response (LeLay and Saulnier, 2007). Therefore, in this study, based on the Flash flood Guidance method, rainfall spatial variability information is introduced in the threshold estimation. As for FFG, the threshold is the number of millimeters of rainfall required to produce a discharge higher than the discharge corresponding to the first level (yellow) warning of the French flood warning service (SCHAPI: Service Central d’Hydrométéorologie et d’Appui à la Prévision des Inondations). The indexes δ1 and δ2 of Zoccatelli et al. (2010), based on the spatial moments of catchment rainfall are used to characterize the rainfall spatial distribution. Rainfall spatial variability impacts on warning threshold and on hydrological processes are then studied. The spatially distributed hydrological model MARINE (Roux et al., 2011), dedicated to flash flood prediction is forced with synthetic rainfall patterns of different spatial distributions. This allows the determination of a warning threshold diagram: knowing the spatial distribution of the rainfall forecast and therefore the 2 indexes δ1 and δ2, the threshold value is read on the diagram. A warning threshold diagram is built for each studied catchment. The proposed methodology is applied on three Mediterranean catchments often submitted to flash floods. The new forecasting method as well as the Flash Flood Guidance method (uniform rainfall threshold) are tested on 25 flash floods events that had occurred on those catchments. Results show a significant impact of rainfall spatial variability. Indeed, it appears that the uniform rainfall threshold (FFG threshold) always overestimates the observed rainfall threshold. The difference between the FFG threshold and the proposed threshold ranges from 8% to 30%. The proposed methodology allows the calculation of a threshold more representative of the observed one. However, results strongly depend on the related event duration and on the catchment properties. For instance, the impact of the rainfall spatial variability seems to be correlated with the catchment size. According to these results, it seems to be interesting to introduce information on the catchment properties in the threshold calculation

Méthodes de régionalisation pour un modèle pluie-débit distribué et à base physique dédié aux crues éclair

Cette étude s’intéresse aux méthodes de régionalisation pour des jeux de paramètres d’un modèle pluie‑débit distribué et à base physique, dédié aux crues éclair. Les performances du modèle MARINE sont testées sur un total de 117 évènements de crues éclair survenues sur des bassins versants de l’arc méditerranéen français. Etant donnée la relative rareté des enregistrements de crues éclair, ce jeu de données représente un échantillon conséquent des paysages et de l’hydrologie des régions allant du piémont pyrénéen à la Provence en passant par les Cévennes et le Vivarais. Des approches de régionalisation basées sur la proximité géographique ou les similarités physiographiques sont testées avec plusieurs combinaisons de descripteurs. Des résultats encourageants sont obtenus avec les deux méthodes de similarités physiographiques basées sur deux ou trois bassins donneurs. Une perte de performance de 10% en régionalisation par rapport à la calibration/validation est relevée pour ces méthodes. Pour 13 bassins versants sur 16, au moins un évènement est simulé avec de bonnes performances. Cette étude met en avant l’importance des informations hydrologiques contenues dans les évènements de calibration disponibles sur site ou sur les bassins donneurs. De plus les techniques de régionalisation produisent de meilleures performances sur les bassins présentant un comportement hydrologique apparemment plus régulier. Le paramètre le plus sensible du modèle MARINE, CZ, contrôlant le volume de sol et ainsi le bilan en eau, est plutôt bien contraint par les approches de régionalisation par similarité grâce aux descripteurs du socle rocheux

Using a multi-hypothesis framework to improve the understanding of flow dynamics during flash floods

A method of multiple working hypotheses was applied to a range of catchments in the Mediterranean area to analyse different types of possible flow dynamics in soils during flash flood events. The distributed, process-oriented model, MARINE, was used to test several representations of subsurface flows, including flows at depth in fractured bedrock and flows through preferential pathways in macropores. Results showed the contrasting performances of the submitted models, revealing different hydrological behaviours among the catchment set. The benchmark study offered a characterisation of the catchments’ reactivity through the description of the hydrograph formation. The quantification of the different flow processes (surface and intra-soil flows) was consistent with the scarce in situ observations, but it remains uncertain as a result of an equifinality issue. The spatial description of the simulated flows over the catchments, made available by the model, enabled the identification of counterbalancing effects between internal flow processes, including the compensation for the water transit time in the hillslopes and in the drainage network. New insights are finally proposed in the form of setting up strategic monitoring and calibration constraints

Friction properties of fluorinated carbons

In boundary lubrication regime, friction reduction and antiwear processes are associated to the presence of additives in the lubricating oils or greases. These processes are due to the formation of protective tribofilms resulting from chemical reactions between the additives and the sliding surfaces, in the physico-chemical conditions of the sliding contact. Conventional antiwear additives mainly consist of transition metal organo phosphate or thiophosphates which present a remarkable efficiency in the case of contacts between ferrous alloys. In the case of non reacting surfaces, these additives become inactive. Recently developped lubrication strategies consist in the use of dispersion in oils of nano additives able to build the protective tribofilm in the sliding contact without reaction with the surfaces. Carbon fluorinated phases, due to their lamellar structure and their high chemical stability even at relatively high temperature (400°C) represent interesting candidates as lubricant nano-additives subjected to present friction reduction, anti wear and anti corrosion actions. This work presents the tribologic behaviour of some carbon fluorinated derivatives such as graphite fluorides, fluorinated carbon nanofibers, fluorinated carbon nanodiscs and fluorinated carbon blacks. The influence, on the tribologic performances, of the structure of the initial carbon phases, of the fluorination rate (0<F/C<1) and the structure of the fluorinated compounds is discussed

Which hydrological activity in weathered bedrock during flash floods? The case of Mediterranean catchments

"Flash flood" term refers to flood with a high specific discharge resulting from storm events of strong intensity. The steepness of numerous small catchments (of a few km2) contributes to a short response time, and the generation of runoff can suddenly turn into devastating floods. In these cases, the discharge seems to be controlled by fast flow transfers. Overland flows explain most of the peak discharge, but subsurface flows can also represent a significant contribution, particularly during the recession limb. Owing to the short time scales, subsurface flows seem to occur into shallow soil horizons. Therefore, hydrological models often use soil characteristics of the upper horizons from BD-sols databases. Unfortunately, experimental data on subsurface flow are not available at the studied space scale (about 100km2). However, many studies (Garambois, 2012; Vannier et al, 2013; Sayama et al, 2011) show that the storage capacities of upper horizons cannot explain alone the water balance during flash floods. As a matter of fact, effective soil storage capacities on Mediterranean catchments often largely exceed the storage capacities of the upper soil layers described in the BD-sols (Vannier et al., 2013). This study implements two methods to assess the actuality of a hydrological dynamic into weathered rock layers during flash floods. These are applied on two past decades observations of flash flood over Mediterranean catchments with different geological characteristics. The first one consists in assessing water storage capacities on weathered rock from observed events data. The second one consists in using a distributed hydrological model dedicated to flash flood events (Roux et al., 2011) to estimate the flow and storage in the deeper soil horizons. Results show that flows through weathered bedrock layers contribute significantly to the flood hydrograph and more particularly on catchments with granitic bedrock. As an example, on the Ardèche catchment, the observed water storage of some events is up to twice the storage capacity of the upper soil layers. Hydrological simulations also estimate an average contribution of 30 % of the deeper layers to the total flood water volume. As a conclusion, the study emphasizes the impact of the weathered bedrock on the hydrological dynamic and shifts future researches toward a more realistic representation of the subsurface flows