{"id":457,"date":"2013-09-03T13:53:54","date_gmt":"2013-09-03T11:53:54","guid":{"rendered":"http:\/\/wp.unil.ch\/risk\/?p=457"},"modified":"2013-10-01T16:09:06","modified_gmt":"2013-10-01T14:09:06","slug":"pascal-horton-improvements-and-global-optimization-of-the-analogue-method-for-statistical-precipitations-forecasting","status":"publish","type":"post","link":"https:\/\/wp.unil.ch\/risk\/pascal-horton-improvements-and-global-optimization-of-the-analogue-method-for-statistical-precipitations-forecasting\/","title":{"rendered":"Pascal Horton: Improvements and global optimization of the analogue method for statistical precipitations forecasting."},"content":{"rendered":"

Pascal Horton<\/em>
\n Directors: Prof. Michel Jaboyedoff, Prof. Charles Obled<\/em>
\n Jury: Prof. Fran\u0018cois Bussy, Dr. Dominique B\u0013erod, Dr. Daniel Cattani, Dr. Vincent Fortin<\/em><\/p>\n

The upper Rhone catchment is sometimes subject to heavy precipitation that can eventually result in floods. The MINERVE project, to which this work belongs, aims at providing tools for flood forecasting and management. For this purpose, actions can be undertaken on dam storage, but this requires forecasting precipitation accurately days beforehand. This is currently done by the numerical weather prediction model of M\u00e9t\u00e9oSuisse. However, due to large uncertainties in the forecasting of extreme events, it was decided that a parallel forecast based on a statistical approach could complement the information available.<\/p>\n

Therefore, we adapted a technique of statistical precipitation forecasting, namely the analogue method, to the alpine context of our catchment. Several parameterizations of the method have been documented and calibrated.<\/p>\n

A substantial part of this study was devoted to programming a forecasting software, which was called Atmoswing. It is designed to process automatically forecasts by means of the analogue method, and to provide a tool for visualizing the results on maps and graphs. It can process many different versions of the analogue method. The software has been operational since mid-2011, and has allowed us to confirm the interest of prediction by analogy.<\/p>\n

As the method is applied here to a new geographical context, a large number of synoptic variables were evaluated. We then confirmed the relevance of the traditional two levels of analogy, which are related first to the atmospheric circulation, and next to the humidity flux, while making improvements to them. As a result, we created new parameterizations that have better forecasting skills than the reference methods considered so far. We also evaluated other improvements, such as the introduction of a shifting time window to find better synoptic analogues at other hours of the day, which show some potential. A 6-hourly time step forecast has been evaluated and was found to bring useful information on precipitation characteristics.<\/p>\n

Finally, we introduced a technique of global optimization: genetic algorithms. These were found to be able to calibrate the analogue method by considering jointly all parameters of the different analogy levels. With that kind of tool we can approach an objectively optimal parameterization.<\/p>\n

As the choice of atmospheric levels and time windows is automated, this technique can result in a gain of time, even if it is relatively demanding in calculations. Thus we were able to improve the analogue method, and to add new degrees of freedom.<\/p>\n

 <\/p>\n

Am\u00e9liorations et optimisation globale de la m\u00e9thode des analogues pour la pr\u00e9vision statistique des pr\u00e9cipitations.<\/h4>\n
D\u00e9veloppement d’un outil de pr\u00e9vision et application op\u00e9rationnelle au bassin du Rh\u00f4ne \u00e0 l’amont du L\u00e9man.<\/h6>\n

Le bassin du Rh\u00f4ne \u00e0 l’amont du L\u00e9man peut \u00eatre sujet \u00e0 de fortes pr\u00e9cipitations en mesure de provoquer des crues significatives. L’objectif du projet MINERVE dans lequel s’inscrit le pr\u00e9sent travail consiste \u00e0 fournir des outils pour la pr\u00e9vision et la gestion des crues par des actions pr\u00e9ventives sur les am\u00e9nagements hydro\u00e9lectriques \u00e0 accumulation. Pour satisfaire ce dernier, il est n\u00e9cessaire de pr\u00e9voir au mieux les cumuls de pr\u00e9cipitations pour les jours suivants. Ceci est actuellement effectu\u00e9 par le mod\u00e8le num\u00e9rique de pr\u00e9vision de M\u00e9t\u00e9oSuisse ; mais, en raison des grandes incertitudes li\u00e9es \u00e0 la quantification des \u00e9v\u00e9nements extr\u00eames, il a \u00e9t\u00e9 d\u00e9cid\u00e9 qu’une approche parall\u00e8le de nature statistique pourrait compl\u00e9ter l’information disponible.<\/p>\n

Ainsi, nous avons adapt\u00e9 la m\u00e9thode des analogues, qui est une technique de pr\u00e9vision statistique des pr\u00e9cipitations, au contexte alpin du bassin d’\u00e9tude. Pour ce faire, plusieurs param\u00e9trisations de la m\u00e9thode ont \u00e9t\u00e9 document\u00e9es et calibr\u00e9es. Afin de prendre en main la m\u00e9thode, nous avons effectu\u00e9 de multiples analyses param\u00e9triques sur les variables synoptiques, mais \u00e9galement sur la constitution de groupements pluviom\u00e9triques.<\/p>\n

Une partie cons\u00e9quente de cette \u00e9tude a \u00e9t\u00e9 consacr\u00e9e \u00e0 la programmation d’un logiciel de pr\u00e9vision automatique par la m\u00e9thode des analogues, ainsi qu’\u00e0 un outil de visualisation des r\u00e9sultats sous forme de cartes et graphiques. Ce logiciel, nomm\u00e9 Atmoswing, permet d’impl\u00e9menter un grand nombre de m\u00e9thodes diff\u00e9rentes de pr\u00e9vision par analogie. L’outil est op\u00e9rationnel depuis mi-2011 et nous a permis de confirmer l’int\u00e9r\u00eat de la pr\u00e9vision par analogie.<\/p>\n

La m\u00e9thode \u00e9tant ici appliqu\u00e9e \u00e0 un nouveau contexte, un grand nombre de variables synoptiques ont \u00e9t\u00e9 \u00e9valu\u00e9es. Nous avons alors confirm\u00e9 l’int\u00e9r\u00eat des deux niveaux d’analogie sur la circulation atmosph\u00e9rique et sur le flux d’humidit\u00e9, tout en apportant des am\u00e9liorations \u00e0 celles-ci. Il en r\u00e9sulte des param\u00e9trisations pr\u00e9sentant des scores de performance sup\u00e9rieurs aux m\u00e9thodes de r\u00e9f\u00e9rence consid\u00e9r\u00e9es. Nous avons \u00e9galement \u00e9valu\u00e9 d’autres am\u00e9liorations, comme l’introduction d’une fen\u00eatre temporelle glissante afin de rechercher de meilleures analogies synoptiques \u00e0 d’autres heures de la journ\u00e9e, ce qui s’est av\u00e9r\u00e9 int\u00e9ressant, tout comme une pr\u00e9vision infrajournali\u00e8re \u00e0 pas de temps de 6 h.<\/p>\n

Finalement, nous avons introduit une technique d’optimisation globale, les algorithmes g\u00e9n\u00e9tiques, capable de calibrer la m\u00e9thode des analogues en consid\u00e9rant tous les param\u00e8tres des diff\u00e9rents niveaux d’analogie de mani\u00e8re conjointe. Avec cette technique, nous pouvons nous approcher objectivement d’une param\u00e9trisation optimale. Le choix des niveaux atmosph\u00e9riques et des fen\u00eatres temporelles et spatiales \u00e9tant automatis\u00e9, cette technique peut engendrer un gain de temps, m\u00eame si elle est relativement exigeante en calculs. Nous avons ainsi pu am\u00e9liorer la m\u00e9thode des analogues, et y ajouter de nouveaux degr\u00e9s de libert\u00e9, notamment des fen\u00eatres spatiales et des pond\u00e9rations diff\u00e9renci\u00e9es selon les niveaux atmosph\u00e9riques retenus.<\/p>\n","protected":false},"excerpt":{"rendered":"

Pascal Horton Directors: Prof. Michel Jaboyedoff, Prof. Charles Obled Jury: Prof. Fran\u0018cois Bussy, Dr. Dominique B\u0013erod, Dr. Daniel Cattani, Dr. Vincent Fortin The upper Rhone catchment is sometimes subject to … <\/p>\n","protected":false},"author":1341,"featured_media":180,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"","_seopress_titles_title":"","_seopress_titles_desc":"","_seopress_robots_index":"","ngg_post_thumbnail":0,"footnotes":""},"categories":[73760],"tags":[51861],"class_list":{"0":"post-457","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-theses_completed","8":"tag-51861"},"_links":{"self":[{"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/posts\/457","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/users\/1341"}],"replies":[{"embeddable":true,"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/comments?post=457"}],"version-history":[{"count":0,"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/posts\/457\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/media\/180"}],"wp:attachment":[{"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/media?parent=457"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/categories?post=457"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wp.unil.ch\/risk\/wp-json\/wp\/v2\/tags?post=457"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}