Abstract. Drought events develop in both space and time and they are therefore best described through summary joint spatio-temporal characteristics, such as mean duration, mean affected area and total magnitude. This paper addresses the issue of future projections of such characteristics of drought events over France through three main research questions: (1) Are downscaled climate projections able to simulate spatio-temporal characteristics of meteorological and agricultural droughts in France over a presentday period? (2) How such characteristics will evolve over the 21st century? (3) How to use standardized drought indices to represent theoretical adaptation scenarios? These questions are addressed using the Isba land surface model, downscaled climate projections from the ARPEGE General Circulation Model under three emissions scenarios, as well as results from a previously performed 50-yr multilevel and multiscale drought reanalysis over France. Spatio-temporal characteristics of meteorological and agricultural drought events are computed using the Standardized Precipitation Index and the Standardized Soil Wetness Index, respectively, and for time scales of 3 and 12 months. Results first show that the distributions of joint spatio-temporal characteristics of observed events are well simulated by the downscaled hydroclimate projections over a present-day period. All spatiotemporal characteristics of drought events are then found to dramatically increase over the 21st century, with stronger changes for agricultural droughts. Two theoretical adaptation scenarios are eventually built based on hypotheses of adaptation to evolving climate and hydrological normals, either retrospective or prospective. The perceived spatio-temporal characteristics of drought events derived from these theoretical adaptation scenarios show much reduced changes, but they call for more realistic scenarios at both the catchment and national scale in order to accurately assess the combined effect of local-scale adaptation and global-scale mitigation.
Résumé (GIEC, 2007). Les études menées sur l'évolu-tion de la ressource en eau en France métropolitaine se sont principalement intéressées aux paramètres météorolo-giques (précipitation notamment) ou hydrologiques, tels que les débits ou les hauteurs des nappes. Ainsi, l'étude des longues séries climatologiques de préci-pitation sur la seconde moitié du XX e siè-cle en France a-t-elle montré une tendance significative à l'augmentation des sécheresses estivales (Moisselin et Dubuisson, 2006 (Vidal et al., 2010a). Des indices ont été déve-loppés à partir des variables de la chaîne SIM pour caractériser les différents types de sécheresses liées à un déficit sur une composante spécifique du cycle de l'eau : précipitation, humidité des sols ou débit des cours d'eau. Une climatologie originale des événements de sécheresse en France a été établie sur la période de 1958de à 2008de (Vidal et al., 2010b. La pertinence de ces travaux a été reconnue par l'attribution du prix Norbert Gerbier-Mumm 2011 de l'Organisation météorologique mondiale (OMM).Cet article rappelle d'abord la méthodo-logie appliquée pour la caractérisation des sécheresses puis il présente les outils opérationnels, dérivés du projet et actuellement disponibles pour le suivi hydrologique en France, au travers de l'analyse de l'événement du printemps 2011. Enfin, les résultats des études à partir des projections climatiques régio-nalisées sur la France seront détaillés pour préciser l'évolution attendue des sécheresses au cours du XXI e siècle et les principales incertitudes associées. La méthodologie de caractérisation des sécheresses Définition des indices de sécheresseUne sécheresse se définit comme un déficit hydrique d'une composante (au moins) du cycle hydrologique (Wilhite et Glantz, 1985
Drought events develop in both space and time and they are therefore best described through summary joint spatio-temporal characteristics, like mean duration, mean affected area and total magnitude. This paper addresses the issue of future projections of such characteristics of drought events over France through three main research questions: (1) are downscaled climate projections able to reproduce spatio-temporal characteristics of meteorological and agricultural droughts in France over a present-day period? (2) How such characteristics will evolve over the 21st century? (3) How to use standardized drought indices to represent theoretical adaptation scenarios? These questions are addressed using the Isba land surface model, downscaled climate projections from the ARPEGE General Circulation Model under three emissions scenarios, as well as results from a previously performed 50-yr multilevel and multiscale drought reanalysis over France. Spatio-temporal characteristics of meteorological and agricultural drought events are computed using the Standardized Precipitation Index and the Standardized Soil Wetness Index, respectively, and for time scales of 3 and 12 months. Results first show that the distributions of joint spatio-temporal characteristics of observed events are well reproduced by the downscaled hydroclimate projections over a present-day period. All spatio-temporal characteristics of drought events are then found to dramatically increase over the 21st century, with stronger changes for agricultural droughts. Two theoretical adaptation scenarios are eventually built based on hypotheses of adaptation to evolving climate and hydrological normals, either retrospective or prospective, and by taking advantage of the statistical properties of the standardized drought indices. The perceived spatio-temporal characteristics of drought events derived from these theoretical adaptation scenarios show much reduced changes, but they call for more realistic scenarios at both the catchment and national scale in order to accurately assess the combined effect of local-scale adaptation and global-scale mitigation
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