Approche régionale pour l’estimation des distributions ponctuelles des pluies journalières dans le Languedoc-Roussillon (France) / Regional approach for the estimation of low-frequency distribution of daily rainfall in the Languedoc-Roussillon region,France

Abstract

Abstract This paper aims to show the benefit of a regional approach for the estimation of rare daily rainfall. The studied region is Languedoc-Roussillon (south of France), where recent exceptional storms necessitate the revision of the statistical distributions, particularly their asymptotic tails over extreme values. The example of a large single-site time series of maximum daily rainfall at Marseille (1864–2002), very close to the studied region, shows a hyper-exponential behaviour for extreme events. At the regional scale, the homogenization process of daily maximum rainfall has been performed by considering that the coefficients of variation of the yearly maximum daily rainfall are stationary over the study zone. Two regional sample studies have been carried out on 15 and 23 gauges, randomly distributed in space, and a similar distribution could be fitted to both samples. As in the case of Marseille, the regional distribution shows a hyper-exponential asymptotic behaviour at the extreme values. The obtained regional distribution provides a systematic method for computation of rare daily rainfall that may be applied in every part of the studied region and, when compared with previous estimations, leads to a significant increase in the depth of rare rainfall.     

Statistics of extremes and estimation of extreme rainfall: I. Theoretical investigation / Statistiques de valeurs extrêmes et estimation de précipitations extrêmes: I. Recherche théorique

Abstract

Abstract The Gumbel distribution has been the prevailing model for quantifying risk associated with extreme rainfall. Several arguments including theoretical reasoning and empirical evidence are supposed to support the appropriateness of the Gumbel distribution. These arguments are examined thoroughly in this work and are put into question. Specifically, theoretical analyses show that the Gumbel distribution is quite unlikely to apply to hydrological extremes and its application may misjudge the risk, as it underestimates seriously the largest extreme rainfall amounts. Besides, it is shown that hydrological records of typical length (some decades) may display a distorted picture of the actual distribution, suggesting that the Gumbel distribution is an appropriate model for rainfall extremes while it is not. In addition, it is shown that the extreme value distribution of type II (EV2) is a more consistent alternative. Based on the theoretical analysis, in the second part of this study an extensive empirical investigation is performed using a collection of 169 of the longest available rainfall records worldwide, each having 100–154 years of data. This verifies the inappropriateness of the Gumbel distribution and the appropriateness of EV2 distribution for rainfall extremes.     

Analysis of a large inter-basin water transfer system in India / Analyse d’un grand système de transfert d’eau inter-bassins en Inde

Abstract

Abstract Inter-basin transfer of water in India is a long-term option to correct the spatial and temporal mismatch of water availability and demand, largely owing to the monsoon climate. This paper is concerned with analysis and preliminary design of a large inter-basin water transfer system in peninsular India. The system covers four major basins and involves operation of 13 major structures. The study was carried out in three stages. First, the surface water deficit in each basin was estimated. Then the net deficit was worked out by considering the availability of groundwater. Finally, the link systems were planned to transfer the amount of water needed to meet the demands with desired reliability.     

Effet auto-épurateur de la lithologie des affleurements géologiques dans un climat semi-aride: cas du bassin versant de l'Oued Mellègue (Nord-Ouest de la Tunisie)

Résumé

Le Nord-Ouest de la Tunisie renferme plus que 81% des eaux de surface et 95% des mines et gîtes miniers. Le bassin versant de l'Oued Mellègue, situé dans cette zone, englobe 13 mines de plomb, zinc, fer, strontium, fluor, barium et phosphates. L'impact des rejets de ces mines sur les eaux de surface a été apprécié grâce à plusieurs compagnes d’échantillonnage. Les résultats d'analyse par ICP/MS de ces échantillons montrent qu'ils renferment des quantités non négligeables d'Al, As, B, Ba, Br, Cd, Co, Cr, Cu, Hg, Mo, Ni, Sr, U et de Zn. L'analyse des ces éléments dans les eaux du Mellègue, de ses affluents et dans la retenue de Nebeur montre que leurs concentrations sont inférieures aux normes d'eau potable. Ce comportement pourrait être dû à la nature des affleurements géologiques formés par des carbonates des argiles et des évaporites, à l'absence de cours d'eau drainant directement les rejets, à la formation de minéraux secondaires caractérisés par une importante rétention des métaux et à l’étendue des bassins versants non pollués.     

4. Hydraulics

Abstract

A solid state event recorder and reader suitable for use with a tipping bucket raingauge are described. The recorder is a small battery operated unit with very low power consumption, capable of recording 64, 8 bit, words. The portable reader unit is used to interrogate it.     

A pore-throat model based on grain-size distribution to quantify gravity-dominated DNAPL instabilities in a water-saturated homogeneous porous medium

A pore-scale network model based on spherical pore bodies and cylindrical pore throats was developed to describe the displacement of water by DNAPL. The pore body size and the pore throat size were given by statistical distributions with user-specified values for the minimum, mean and maximum sizes. The numerical model was applied to a laboratory experiment conducted on a sand-filled glass column. The parameters relative to pore body size and pore throat size that were used in the construction of the equivalent network were derived from the discrete grain-size distribution of the real porous medium. The calculated arrival times of the DNAPL front were compared with those measured using optic fibre sensors placed at different points on the control section of the experimental device. Furthermore, the model simulated DNAPL pressure measured at the entrance section of the system. In general, the numerical results obtained with the model were in good agreement with the actual measurements.     

Iron Isotope Variations in Coastal Seawater Determined by Multicollector ICP-MS

In this paper, we applied a reliable technique for measuring Fe isotope variations in coastal seawater at nanomolar levels. Iron was directly pre-concentrated from acidified seawater samples onto a nitrilotriacetic acid chelating resin and further purified using anion-exchange resin. Sample recovery, determined using a standard addition method, was essentially quantitative. Iron was then determined using a high-resolution multicollector ICP-MS (Neptune) coupled to an ApexQ desolvation introduction system. The external precision for δ⁵⁶Fe values was 0.11‰ (2s) when using total a Fe quantity between 25 and 100 ng. We initially applied this technique to measure the Fe isotope composition of dissolved Fe from several coastal environments in the north-eastern United States and we observed a range of δ⁵⁶Fe values between -0.9‰ and 0.1‰ relative to the IRMM-14 reference material. Iron isotope compositions of several reference water materials for inter-laboratory comparisons were also reported. Our results suggest that iron in coastal seawater, derived from benthic diagenesis and/or groundwater has negative Fe isotopic signatures that are distinct from other iron sources such as atmospheric deposition and rivers.     

Regulating public space on the beachfronts of Rio de Janeiro

Despite the fortification of buildings, streets, and public squares, Rio de Janeiro's beaches remain widely regarded as democratic spaces of social diversity and accessibility. Our study revisits the question of Rio's “democratic” beachfronts, based on local interviews, field observations, official reports, and newspaper accounts. We focus on historical and contemporary perceptions of planning, privatization, and public-order programs on the city's southern seaside. Institutional discourses have justified increasing regulation to combat threats of disorder and insecurity. While residents value the relative openness of beachfronts, they also acknowledge issues of safety, social segmentation, and subtle forms of bias. The public generally applauds recent “Shock of Order” policing and commercial revitalization, although critics lament the loss of traditional freedoms for informal beach vendors and casual sports. These paradoxes highlight enduring tensions between social order and hierarchy on one hand, and democratic rights and equality on the other.     

(What Geographers Should Know About) The State of U.S. and Canadian Academic Professional Associations’ Engagement with Mental Health Practices and Policies

The professional organizations to which geographers belong and by which they are represented have a civic duty and ethical responsibility to educate their members about mental health issues in their professions and, by default, their work environments. And yet national-level professional associations in North America are lagging behind universities in adopting initiatives, commissioning reports, and looking into best practices around the mental health of their members. A survey of the Web sites of sixty-six professional associations in the social sciences, geographical sciences, and humanities in the United States and Canada reveals an uneven presence of attention to mental health issues in terms of their members’ research on mental health issues, awareness of mental health as a professional development issue, and engagement in mental health advocacy and public outreach. In this article, we explore how geography’s professional organizations compare to others with respect to these issues and suggest ways in which they can develop their own mental health protocols to address the crisis of mental health in the academy. Key Words: Academic professional associations, American Association of Geographers, Canadian Association of Geographers, mental health, mental health practices and policies.