1 The hydrological impact of the mediterranean forest: a review of French research Claude Cosandey* ; Vasken Andréassian** ; Claude Martin*** ; JF Didon-Lescot*** Jacques Lavabre **** ; Nathalie Folton **** ; Nicolle Mathys***** ; Didier Richard***** * Laboratoire de Géographie Physique, UMR 8591 du CNRS, 1 Place Aristide Briand, F-92190 Meudon, France. E-mail : cosandey@cnrs-bellevue.fr ** Cemagref, URE Qualité et fonctionnement hydrologique des milieux aquatiques, BP 44, F-92163 Antony cedex. E-Mail : vasken.andreassian@cemagref.fr *** UMR 6012 "ESPACE", Equipe GVE, Département de Géographie, 98 Boulevard Edouard Herriot, BP 3209, F-06 204 Nice cedex 3, France. E-mail : martincl@infonie.fr et didonles@unice.fr **** Cemagref, B.P. 31, Le Tholonet, F-13 612 Aix-en-Provence cedex 1, France. E-Mail : jacques.lavabre@cemagref.fr et nathalie.folton@cemagref.fr ****** Cemagref, 2 Rue de la papeterie, BP 76, 38402 Saint-Martin-d'Hères, France. E-Mail : nicolle.mathys@cemagref.fr et didier.richard@cemagref.fr Abstract Forest hydrology studies carried out in France have focused mainly on the Mediterranean part of the country. Three experimental catchments groups exist and have been monitored over a long period. Some forested catchment (Draix catchment) underwent no change during the study period, while others experienced either clear cutting (Lozère catchment) or forest fires (part of the Réal Collobrier catchments). In each case studied, the behaviour of the forested catchment was compared to that of a control catchment. Included with the experimental catchments studies are the results of research with a fundamentally different approach. The research is based on a statistical study of the interrelated development of afforestation rates and runoff characteristics for average-sized catchments (around 100 km 2 ) in that part of the southern French Massif Central which is subject to Mediterranean rainfall conditions. The results differ considerably from one site to another, indicating the degree of complexity of the rainfall/discharge relationship. An increase in extreme flood events due to forest disturbance could by no means be confirmed in every case. A closer look at the hydrological behaviour of the catchments cleared up the apparent inconsistencies. It is mainly the contrast between bare soil and vegetated soil, rather than between forest and other types of vegetation witch is relevant in explaining the hydrological behaviour. Keywords: Forest hydrology; Floods; Annual discharge; Mediterranean climate. 1 - Introduction There is much controversy about the hydrological impact of forests with respect to flood events, low flows, and even annual runoff (Bosch and Hewlett, 1982; Bruinjzeel, 1990; Fritsch, 1992; Calder, 1998). It is true that the influence of forest on flows depends on a large number of factors, which explains the widely dissimilar results observed. In the South of France, research on the subject focused on three research catchments in the humid Mediterranean zone. The sites differ in pedological and geomorphological characteristics, although all three are subject to heavy rainfall in autumn and sometimes during the summer. The wide variety of responses observed prompted an attempt to isolate the hydrological mechanisms that would explain the effect of plant cover on catchment hydrological behaviour. hal-00327222, version 1 - 7 Oct 2008 Author manuscript, published in "Journal of Hydrology 301, 4 (2005) 235-249"